nodeWindowAgg.c

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/*-------------------------------------------------------------------------
 *
 * nodeWindowAgg.c
 *    routines to handle WindowAgg nodes.
 *
 * A WindowAgg node evaluates "window functions" across suitable partitions
 * of the input tuple set.  Any one WindowAgg works for just a single window
 * specification, though it can evaluate multiple window functions sharing
 * identical window specifications.  The input tuples are required to be
 * delivered in sorted order, with the PARTITION BY columns (if any) as
 * major sort keys and the ORDER BY columns (if any) as minor sort keys.
 * (The planner generates a stack of WindowAggs with intervening Sort nodes
 * as needed, if a query involves more than one window specification.)
 *
 * Since window functions can require access to any or all of the rows in
 * the current partition, we accumulate rows of the partition into a
 * tuplestore.  The window functions are called using the WindowObject API
 * so that they can access those rows as needed.
 *
 * We also support using plain aggregate functions as window functions.
 * For these, the regular Agg-node environment is emulated for each partition.
 * As required by the SQL spec, the output represents the value of the
 * aggregate function over all rows in the current row's window frame.
 *
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeWindowAgg.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "catalog/objectaccess.h"
#include "catalog/pg_aggregate.h"
#include "catalog/pg_proc.h"
#include "executor/executor.h"
#include "executor/nodeWindowAgg.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "optimizer/optimizer.h"
#include "parser/parse_agg.h"
#include "parser/parse_coerce.h"
#include "utils/acl.h"
#include "utils/builtins.h"
#include "utils/datum.h"
#include "utils/expandeddatum.h"
#include "utils/lsyscache.h"
#include "utils/memutils.h"
#include "utils/regproc.h"
#include "utils/syscache.h"
#include "windowapi.h"

/*
 * All the window function APIs are called with this object, which is passed
 * to window functions as fcinfo->context.
 */
typedef struct WindowObjectData
{
    NodeTag     type;
    WindowAggState *winstate;   /* parent WindowAggState */
    List       *argstates;      /* ExprState trees for fn's arguments */
    void       *localmem;       /* WinGetPartitionLocalMemory's chunk */
    int         markptr;        /* tuplestore mark pointer for this fn */
    int         readptr;        /* tuplestore read pointer for this fn */
    int64       markpos;        /* row that markptr is positioned on */
    int64       seekpos;        /* row that readptr is positioned on */
} WindowObjectData;

/*
 * We have one WindowStatePerFunc struct for each window function and
 * window aggregate handled by this node.
 */
typedef struct WindowStatePerFuncData
{
    /* Links to WindowFunc expr and state nodes this working state is for */
    WindowFuncExprState *wfuncstate;
    WindowFunc *wfunc;

    int         numArguments;   /* number of arguments */

    FmgrInfo    flinfo;         /* fmgr lookup data for window function */

    Oid         winCollation;   /* collation derived for window function */

    /*
     * We need the len and byval info for the result of each function in order
     * to know how to copy/delete values.
     */
    int16       resulttypeLen;
    bool        resulttypeByVal;

    bool        plain_agg;      /* is it just a plain aggregate function? */
    int         aggno;          /* if so, index of its WindowStatePerAggData */

    WindowObject winobj;        /* object used in window function API */
}           WindowStatePerFuncData;

/*
 * For plain aggregate window functions, we also have one of these.
 */
typedef struct WindowStatePerAggData
{
    /* Oids of transition functions */
    Oid         transfn_oid;
    Oid         invtransfn_oid; /* may be InvalidOid */
    Oid         finalfn_oid;    /* may be InvalidOid */

    /*
     * fmgr lookup data for transition functions --- only valid when
     * corresponding oid is not InvalidOid.  Note in particular that fn_strict
     * flags are kept here.
     */
    FmgrInfo    transfn;
    FmgrInfo    invtransfn;
    FmgrInfo    finalfn;

    int         numFinalArgs;   /* number of arguments to pass to finalfn */

    /*
     * initial value from pg_aggregate entry
     */
    Datum       initValue;
    bool        initValueIsNull;

    /*
     * cached value for current frame boundaries
     */
    Datum       resultValue;
    bool        resultValueIsNull;

    /*
     * We need the len and byval info for the agg's input, result, and
     * transition data types in order to know how to copy/delete values.
     */
    int16       inputtypeLen,
                resulttypeLen,
                transtypeLen;
    bool        inputtypeByVal,
                resulttypeByVal,
                transtypeByVal;

    int         wfuncno;        /* index of associated WindowStatePerFuncData */

    /* Context holding transition value and possibly other subsidiary data */
    MemoryContext aggcontext;   /* may be private, or winstate->aggcontext */

    /* Current transition value */
    Datum       transValue;     /* current transition value */
    bool        transValueIsNull;

    int64       transValueCount;    /* number of currently-aggregated rows */

    /* Data local to eval_windowaggregates() */
    bool        restart;        /* need to restart this agg in this cycle? */
} WindowStatePerAggData;

static void initialize_windowaggregate(WindowAggState *winstate,
                                       WindowStatePerFunc perfuncstate,
                                       WindowStatePerAgg peraggstate);
static void advance_windowaggregate(WindowAggState *winstate,
                                    WindowStatePerFunc perfuncstate,
                                    WindowStatePerAgg peraggstate);
static bool advance_windowaggregate_base(WindowAggState *winstate,
                                         WindowStatePerFunc perfuncstate,
                                         WindowStatePerAgg peraggstate);
static void finalize_windowaggregate(WindowAggState *winstate,
                                     WindowStatePerFunc perfuncstate,
                                     WindowStatePerAgg peraggstate,
                                     Datum *result, bool *isnull);

static void eval_windowaggregates(WindowAggState *winstate);
static void eval_windowfunction(WindowAggState *winstate,
                                WindowStatePerFunc perfuncstate,
                                Datum *result, bool *isnull);

static void begin_partition(WindowAggState *winstate);
static void spool_tuples(WindowAggState *winstate, int64 pos);
static void release_partition(WindowAggState *winstate);

static int  row_is_in_frame(WindowAggState *winstate, int64 pos,
                            TupleTableSlot *slot);
static void update_frameheadpos(WindowAggState *winstate);
static void update_frametailpos(WindowAggState *winstate);
static void update_grouptailpos(WindowAggState *winstate);

static WindowStatePerAggData *initialize_peragg(WindowAggState *winstate,
                                                WindowFunc *wfunc,
                                                WindowStatePerAgg peraggstate);
static Datum GetAggInitVal(Datum textInitVal, Oid transtype);

static bool are_peers(WindowAggState *winstate, TupleTableSlot *slot1,
                      TupleTableSlot *slot2);
static bool window_gettupleslot(WindowObject winobj, int64 pos,
                                TupleTableSlot *slot);


/*
 * initialize_windowaggregate
 * parallel to initialize_aggregates in nodeAgg.c
 */
static void
initialize_windowaggregate(WindowAggState *winstate,
                           WindowStatePerFunc perfuncstate,
                           WindowStatePerAgg peraggstate)
{
    MemoryContext oldContext;

    /*
     * If we're using a private aggcontext, we may reset it here.  But if the
     * context is shared, we don't know which other aggregates may still need
     * it, so we must leave it to the caller to reset at an appropriate time.
     */
    if (peraggstate->aggcontext != winstate->aggcontext)
        MemoryContextResetAndDeleteChildren(peraggstate->aggcontext);

    if (peraggstate->initValueIsNull)
        peraggstate->transValue = peraggstate->initValue;
    else
    {
        oldContext = MemoryContextSwitchTo(peraggstate->aggcontext);
        peraggstate->transValue = datumCopy(peraggstate->initValue,
                                            peraggstate->transtypeByVal,
                                            peraggstate->transtypeLen);
        MemoryContextSwitchTo(oldContext);
    }
    peraggstate->transValueIsNull = peraggstate->initValueIsNull;
    peraggstate->transValueCount = 0;
    peraggstate->resultValue = (Datum) 0;
    peraggstate->resultValueIsNull = true;
}

/*
 * advance_windowaggregate
 * parallel to advance_aggregates in nodeAgg.c
 */
static void
advance_windowaggregate(WindowAggState *winstate,
                        WindowStatePerFunc perfuncstate,
                        WindowStatePerAgg peraggstate)
{
    LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
    WindowFuncExprState *wfuncstate = perfuncstate->wfuncstate;
    int         numArguments = perfuncstate->numArguments;
    Datum       newVal;
    ListCell   *arg;
    int         i;
    MemoryContext oldContext;
    ExprContext *econtext = winstate->tmpcontext;
    ExprState  *filter = wfuncstate->aggfilter;

    oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);

    /* Skip anything FILTERed out */
    if (filter)
    {
        bool        isnull;
        Datum       res = ExecEvalExpr(filter, econtext, &isnull);

        if (isnull || !DatumGetBool(res))
        {
            MemoryContextSwitchTo(oldContext);
            return;
        }
    }

    /* We start from 1, since the 0th arg will be the transition value */
    i = 1;
    foreach(arg, wfuncstate->args)
    {
        ExprState  *argstate = (ExprState *) lfirst(arg);

        fcinfo->args[i].value = ExecEvalExpr(argstate, econtext,
                                             &fcinfo->args[i].isnull);
        i++;
    }

    if (peraggstate->transfn.fn_strict)
    {
        /*
         * For a strict transfn, nothing happens when there's a NULL input; we
         * just keep the prior transValue.  Note transValueCount doesn't
         * change either.
         */
        for (i = 1; i <= numArguments; i++)
        {
            if (fcinfo->args[i].isnull)
            {
                MemoryContextSwitchTo(oldContext);
                return;
            }
        }

        /*
         * For strict transition functions with initial value NULL we use the
         * first non-NULL input as the initial state.  (We already checked
         * that the agg's input type is binary-compatible with its transtype,
         * so straight copy here is OK.)
         *
         * We must copy the datum into aggcontext if it is pass-by-ref.  We do
         * not need to pfree the old transValue, since it's NULL.
         */
        if (peraggstate->transValueCount == 0 && peraggstate->transValueIsNull)
        {
            MemoryContextSwitchTo(peraggstate->aggcontext);
            peraggstate->transValue = datumCopy(fcinfo->args[1].value,
                                                peraggstate->transtypeByVal,
                                                peraggstate->transtypeLen);
            peraggstate->transValueIsNull = false;
            peraggstate->transValueCount = 1;
            MemoryContextSwitchTo(oldContext);
            return;
        }

        if (peraggstate->transValueIsNull)
        {
            /*
             * Don't call a strict function with NULL inputs.  Note it is
             * possible to get here despite the above tests, if the transfn is
             * strict *and* returned a NULL on a prior cycle.  If that happens
             * we will propagate the NULL all the way to the end.  That can
             * only happen if there's no inverse transition function, though,
             * since we disallow transitions back to NULL when there is one.
             */
            MemoryContextSwitchTo(oldContext);
            Assert(!OidIsValid(peraggstate->invtransfn_oid));
            return;
        }
    }

    /*
     * OK to call the transition function.  Set winstate->curaggcontext while
     * calling it, for possible use by AggCheckCallContext.
     */
    InitFunctionCallInfoData(*fcinfo, &(peraggstate->transfn),
                             numArguments + 1,
                             perfuncstate->winCollation,
                             (void *) winstate, NULL);
    fcinfo->args[0].value = peraggstate->transValue;
    fcinfo->args[0].isnull = peraggstate->transValueIsNull;
    winstate->curaggcontext = peraggstate->aggcontext;
    newVal = FunctionCallInvoke(fcinfo);
    winstate->curaggcontext = NULL;

    /*
     * Moving-aggregate transition functions must not return null, see
     * advance_windowaggregate_base().
     */
    if (fcinfo->isnull && OidIsValid(peraggstate->invtransfn_oid))
        ereport(ERROR,
                (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                 errmsg("moving-aggregate transition function must not return null")));

    /*
     * We must track the number of rows included in transValue, since to
     * remove the last input, advance_windowaggregate_base() mustn't call the
     * inverse transition function, but simply reset transValue back to its
     * initial value.
     */
    peraggstate->transValueCount++;

    /*
     * If pass-by-ref datatype, must copy the new value into aggcontext and
     * free the prior transValue.  But if transfn returned a pointer to its
     * first input, we don't need to do anything.  Also, if transfn returned a
     * pointer to a R/W expanded object that is already a child of the
     * aggcontext, assume we can adopt that value without copying it.
     */
    if (!peraggstate->transtypeByVal &&
        DatumGetPointer(newVal) != DatumGetPointer(peraggstate->transValue))
    {
        if (!fcinfo->isnull)
        {
            MemoryContextSwitchTo(peraggstate->aggcontext);
            if (DatumIsReadWriteExpandedObject(newVal,
                                               false,
                                               peraggstate->transtypeLen) &&
                MemoryContextGetParent(DatumGetEOHP(newVal)->eoh_context) == CurrentMemoryContext)
                 /* do nothing */ ;
            else
                newVal = datumCopy(newVal,
                                   peraggstate->transtypeByVal,
                                   peraggstate->transtypeLen);
        }
        if (!peraggstate->transValueIsNull)
        {
            if (DatumIsReadWriteExpandedObject(peraggstate->transValue,
                                               false,
                                               peraggstate->transtypeLen))
                DeleteExpandedObject(peraggstate->transValue);
            else
                pfree(DatumGetPointer(peraggstate->transValue));
        }
    }

    MemoryContextSwitchTo(oldContext);
    peraggstate->transValue = newVal;
    peraggstate->transValueIsNull = fcinfo->isnull;
}

/*
 * advance_windowaggregate_base
 * Remove the oldest tuple from an aggregation.
 *
 * This is very much like advance_windowaggregate, except that we will call
 * the inverse transition function (which caller must have checked is
 * available).
 *
 * Returns true if we successfully removed the current row from this
 * aggregate, false if not (in the latter case, caller is responsible
 * for cleaning up by restarting the aggregation).
 */
static bool
advance_windowaggregate_base(WindowAggState *winstate,
                             WindowStatePerFunc perfuncstate,
                             WindowStatePerAgg peraggstate)
{
    LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
    WindowFuncExprState *wfuncstate = perfuncstate->wfuncstate;
    int         numArguments = perfuncstate->numArguments;
    Datum       newVal;
    ListCell   *arg;
    int         i;
    MemoryContext oldContext;
    ExprContext *econtext = winstate->tmpcontext;
    ExprState  *filter = wfuncstate->aggfilter;

    oldContext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);

    /* Skip anything FILTERed out */
    if (filter)
    {
        bool        isnull;
        Datum       res = ExecEvalExpr(filter, econtext, &isnull);

        if (isnull || !DatumGetBool(res))
        {
            MemoryContextSwitchTo(oldContext);
            return true;
        }
    }

    /* We start from 1, since the 0th arg will be the transition value */
    i = 1;
    foreach(arg, wfuncstate->args)
    {
        ExprState  *argstate = (ExprState *) lfirst(arg);

        fcinfo->args[i].value = ExecEvalExpr(argstate, econtext,
                                             &fcinfo->args[i].isnull);
        i++;
    }

    if (peraggstate->invtransfn.fn_strict)
    {
        /*
         * For a strict (inv)transfn, nothing happens when there's a NULL
         * input; we just keep the prior transValue.  Note transValueCount
         * doesn't change either.
         */
        for (i = 1; i <= numArguments; i++)
        {
            if (fcinfo->args[i].isnull)
            {
                MemoryContextSwitchTo(oldContext);
                return true;
            }
        }
    }

    /* There should still be an added but not yet removed value */
    Assert(peraggstate->transValueCount > 0);

    /*
     * In moving-aggregate mode, the state must never be NULL, except possibly
     * before any rows have been aggregated (which is surely not the case at
     * this point).  This restriction allows us to interpret a NULL result
     * from the inverse function as meaning "sorry, can't do an inverse
     * transition in this case".  We already checked this in
     * advance_windowaggregate, but just for safety, check again.
     */
    if (peraggstate->transValueIsNull)
        elog(ERROR, "aggregate transition value is NULL before inverse transition");

    /*
     * We mustn't use the inverse transition function to remove the last
     * input.  Doing so would yield a non-NULL state, whereas we should be in
     * the initial state afterwards which may very well be NULL.  So instead,
     * we simply re-initialize the aggregate in this case.
     */
    if (peraggstate->transValueCount == 1)
    {
        MemoryContextSwitchTo(oldContext);
        initialize_windowaggregate(winstate,
                                   &winstate->perfunc[peraggstate->wfuncno],
                                   peraggstate);
        return true;
    }

    /*
     * OK to call the inverse transition function.  Set
     * winstate->curaggcontext while calling it, for possible use by
     * AggCheckCallContext.
     */
    InitFunctionCallInfoData(*fcinfo, &(peraggstate->invtransfn),
                             numArguments + 1,
                             perfuncstate->winCollation,
                             (void *) winstate, NULL);
    fcinfo->args[0].value = peraggstate->transValue;
    fcinfo->args[0].isnull = peraggstate->transValueIsNull;
    winstate->curaggcontext = peraggstate->aggcontext;
    newVal = FunctionCallInvoke(fcinfo);
    winstate->curaggcontext = NULL;

    /*
     * If the function returns NULL, report failure, forcing a restart.
     */
    if (fcinfo->isnull)
    {
        MemoryContextSwitchTo(oldContext);
        return false;
    }

    /* Update number of rows included in transValue */
    peraggstate->transValueCount--;

    /*
     * If pass-by-ref datatype, must copy the new value into aggcontext and
     * free the prior transValue.  But if invtransfn returned a pointer to its
     * first input, we don't need to do anything.  Also, if invtransfn
     * returned a pointer to a R/W expanded object that is already a child of
     * the aggcontext, assume we can adopt that value without copying it.
     *
     * Note: the checks for null values here will never fire, but it seems
     * best to have this stanza look just like advance_windowaggregate.
     */
    if (!peraggstate->transtypeByVal &&
        DatumGetPointer(newVal) != DatumGetPointer(peraggstate->transValue))
    {
        if (!fcinfo->isnull)
        {
            MemoryContextSwitchTo(peraggstate->aggcontext);
            if (DatumIsReadWriteExpandedObject(newVal,
                                               false,
                                               peraggstate->transtypeLen) &&
                MemoryContextGetParent(DatumGetEOHP(newVal)->eoh_context) == CurrentMemoryContext)
                 /* do nothing */ ;
            else
                newVal = datumCopy(newVal,
                                   peraggstate->transtypeByVal,
                                   peraggstate->transtypeLen);
        }
        if (!peraggstate->transValueIsNull)
        {
            if (DatumIsReadWriteExpandedObject(peraggstate->transValue,
                                               false,
                                               peraggstate->transtypeLen))
                DeleteExpandedObject(peraggstate->transValue);
            else
                pfree(DatumGetPointer(peraggstate->transValue));
        }
    }

    MemoryContextSwitchTo(oldContext);
    peraggstate->transValue = newVal;
    peraggstate->transValueIsNull = fcinfo->isnull;

    return true;
}

/*
 * finalize_windowaggregate
 * parallel to finalize_aggregate in nodeAgg.c
 */
static void
finalize_windowaggregate(WindowAggState *winstate,
                         WindowStatePerFunc perfuncstate,
                         WindowStatePerAgg peraggstate,
                         Datum *result, bool *isnull)
{
    MemoryContext oldContext;

    oldContext = MemoryContextSwitchTo(winstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory);

    /*
     * Apply the agg's finalfn if one is provided, else return transValue.
     */
    if (OidIsValid(peraggstate->finalfn_oid))
    {
        LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
        int         numFinalArgs = peraggstate->numFinalArgs;
        bool        anynull;
        int         i;

        InitFunctionCallInfoData(fcinfodata.fcinfo, &(peraggstate->finalfn),
                                 numFinalArgs,
                                 perfuncstate->winCollation,
                                 (void *) winstate, NULL);
        fcinfo->args[0].value =
            MakeExpandedObjectReadOnly(peraggstate->transValue,
                                       peraggstate->transValueIsNull,
                                       peraggstate->transtypeLen);
        fcinfo->args[0].isnull = peraggstate->transValueIsNull;
        anynull = peraggstate->transValueIsNull;

        /* Fill any remaining argument positions with nulls */
        for (i = 1; i < numFinalArgs; i++)
        {
            fcinfo->args[i].value = (Datum) 0;
            fcinfo->args[i].isnull = true;
            anynull = true;
        }

        if (fcinfo->flinfo->fn_strict && anynull)
        {
            /* don't call a strict function with NULL inputs */
            *result = (Datum) 0;
            *isnull = true;
        }
        else
        {
            winstate->curaggcontext = peraggstate->aggcontext;
            *result = FunctionCallInvoke(fcinfo);
            winstate->curaggcontext = NULL;
            *isnull = fcinfo->isnull;
        }
    }
    else
    {
        /* Don't need MakeExpandedObjectReadOnly; datumCopy will copy it */
        *result = peraggstate->transValue;
        *isnull = peraggstate->transValueIsNull;
    }

    /*
     * If result is pass-by-ref, make sure it is in the right context.
     */
    if (!peraggstate->resulttypeByVal && !*isnull &&
        !MemoryContextContains(CurrentMemoryContext,
                               DatumGetPointer(*result)))
        *result = datumCopy(*result,
                            peraggstate->resulttypeByVal,
                            peraggstate->resulttypeLen);
    MemoryContextSwitchTo(oldContext);
}

/*
 * eval_windowaggregates
 * evaluate plain aggregates being used as window functions
 *
 * This differs from nodeAgg.c in two ways.  First, if the window's frame
 * start position moves, we use the inverse transition function (if it exists)
 * to remove rows from the transition value.  And second, we expect to be
 * able to call aggregate final functions repeatedly after aggregating more
 * data onto the same transition value.  This is not a behavior required by
 * nodeAgg.c.
 */
static void
eval_windowaggregates(WindowAggState *winstate)
{
    WindowStatePerAgg peraggstate;
    int         wfuncno,
                numaggs,
                numaggs_restart,
                i;
    int64       aggregatedupto_nonrestarted;
    MemoryContext oldContext;
    ExprContext *econtext;
    WindowObject agg_winobj;
    TupleTableSlot *agg_row_slot;
    TupleTableSlot *temp_slot;

    numaggs = winstate->numaggs;
    if (numaggs == 0)
        return;                 /* nothing to do */

    /* final output execution is in ps_ExprContext */
    econtext = winstate->ss.ps.ps_ExprContext;
    agg_winobj = winstate->agg_winobj;
    agg_row_slot = winstate->agg_row_slot;
    temp_slot = winstate->temp_slot_1;

    /*
     * If the window's frame start clause is UNBOUNDED_PRECEDING and no
     * exclusion clause is specified, then the window frame consists of a
     * contiguous group of rows extending forward from the start of the
     * partition, and rows only enter the frame, never exit it, as the current
     * row advances forward.  This makes it possible to use an incremental
     * strategy for evaluating aggregates: we run the transition function for
     * each row added to the frame, and run the final function whenever we
     * need the current aggregate value.  This is considerably more efficient
     * than the naive approach of re-running the entire aggregate calculation
     * for each current row.  It does assume that the final function doesn't
     * damage the running transition value, but we have the same assumption in
     * nodeAgg.c too (when it rescans an existing hash table).
     *
     * If the frame start does sometimes move, we can still optimize as above
     * whenever successive rows share the same frame head, but if the frame
     * head moves beyond the previous head we try to remove those rows using
     * the aggregate's inverse transition function.  This function restores
     * the aggregate's current state to what it would be if the removed row
     * had never been aggregated in the first place.  Inverse transition
     * functions may optionally return NULL, indicating that the function was
     * unable to remove the tuple from aggregation.  If this happens, or if
     * the aggregate doesn't have an inverse transition function at all, we
     * must perform the aggregation all over again for all tuples within the
     * new frame boundaries.
     *
     * If there's any exclusion clause, then we may have to aggregate over a
     * non-contiguous set of rows, so we punt and recalculate for every row.
     * (For some frame end choices, it might be that the frame is always
     * contiguous anyway, but that's an optimization to investigate later.)
     *
     * In many common cases, multiple rows share the same frame and hence the
     * same aggregate value. (In particular, if there's no ORDER BY in a RANGE
     * window, then all rows are peers and so they all have window frame equal
     * to the whole partition.)  We optimize such cases by calculating the
     * aggregate value once when we reach the first row of a peer group, and
     * then returning the saved value for all subsequent rows.
     *
     * 'aggregatedupto' keeps track of the first row that has not yet been
     * accumulated into the aggregate transition values.  Whenever we start a
     * new peer group, we accumulate forward to the end of the peer group.
     */

    /*
     * First, update the frame head position.
     *
     * The frame head should never move backwards, and the code below wouldn't
     * cope if it did, so for safety we complain if it does.
     */
    update_frameheadpos(winstate);
    if (winstate->frameheadpos < winstate->aggregatedbase)
        elog(ERROR, "window frame head moved backward");

    /*
     * If the frame didn't change compared to the previous row, we can re-use
     * the result values that were previously saved at the bottom of this
     * function.  Since we don't know the current frame's end yet, this is not
     * possible to check for fully.  But if the frame end mode is UNBOUNDED
     * FOLLOWING or CURRENT ROW, no exclusion clause is specified, and the
     * current row lies within the previous row's frame, then the two frames'
     * ends must coincide.  Note that on the first row aggregatedbase ==
     * aggregatedupto, meaning this test must fail, so we don't need to check
     * the "there was no previous row" case explicitly here.
     */
    if (winstate->aggregatedbase == winstate->frameheadpos &&
        (winstate->frameOptions & (FRAMEOPTION_END_UNBOUNDED_FOLLOWING |
                                   FRAMEOPTION_END_CURRENT_ROW)) &&
        !(winstate->frameOptions & FRAMEOPTION_EXCLUSION) &&
        winstate->aggregatedbase <= winstate->currentpos &&
        winstate->aggregatedupto > winstate->currentpos)
    {
        for (i = 0; i < numaggs; i++)
        {
            peraggstate = &winstate->peragg[i];
            wfuncno = peraggstate->wfuncno;
            econtext->ecxt_aggvalues[wfuncno] = peraggstate->resultValue;
            econtext->ecxt_aggnulls[wfuncno] = peraggstate->resultValueIsNull;
        }
        return;
    }

    /*----------
     * Initialize restart flags.
     *
     * We restart the aggregation:
     *   - if we're processing the first row in the partition, or
     *   - if the frame's head moved and we cannot use an inverse
     *     transition function, or
     *   - we have an EXCLUSION clause, or
     *   - if the new frame doesn't overlap the old one
     *
     * Note that we don't strictly need to restart in the last case, but if
     * we're going to remove all rows from the aggregation anyway, a restart
     * surely is faster.
     *----------
     */
    numaggs_restart = 0;
    for (i = 0; i < numaggs; i++)
    {
        peraggstate = &winstate->peragg[i];
        if (winstate->currentpos == 0 ||
            (winstate->aggregatedbase != winstate->frameheadpos &&
             !OidIsValid(peraggstate->invtransfn_oid)) ||
            (winstate->frameOptions & FRAMEOPTION_EXCLUSION) ||
            winstate->aggregatedupto <= winstate->frameheadpos)
        {
            peraggstate->restart = true;
            numaggs_restart++;
        }
        else
            peraggstate->restart = false;
    }

    /*
     * If we have any possibly-moving aggregates, attempt to advance
     * aggregatedbase to match the frame's head by removing input rows that
     * fell off the top of the frame from the aggregations.  This can fail,
     * i.e. advance_windowaggregate_base() can return false, in which case
     * we'll restart that aggregate below.
     */
    while (numaggs_restart < numaggs &&
           winstate->aggregatedbase < winstate->frameheadpos)
    {
        /*
         * Fetch the next tuple of those being removed. This should never fail
         * as we should have been here before.
         */
        if (!window_gettupleslot(agg_winobj, winstate->aggregatedbase,
                                 temp_slot))
            elog(ERROR, "could not re-fetch previously fetched frame row");

        /* Set tuple context for evaluation of aggregate arguments */
        winstate->tmpcontext->ecxt_outertuple = temp_slot;

        /*
         * Perform the inverse transition for each aggregate function in the
         * window, unless it has already been marked as needing a restart.
         */
        for (i = 0; i < numaggs; i++)
        {
            bool        ok;

            peraggstate = &winstate->peragg[i];
            if (peraggstate->restart)
                continue;

            wfuncno = peraggstate->wfuncno;
            ok = advance_windowaggregate_base(winstate,
                                              &winstate->perfunc[wfuncno],
                                              peraggstate);
            if (!ok)
            {
                /* Inverse transition function has failed, must restart */
                peraggstate->restart = true;
                numaggs_restart++;
            }
        }

        /* Reset per-input-tuple context after each tuple */
        ResetExprContext(winstate->tmpcontext);

        /* And advance the aggregated-row state */
        winstate->aggregatedbase++;
        ExecClearTuple(temp_slot);
    }

    /*
     * If we successfully advanced the base rows of all the aggregates,
     * aggregatedbase now equals frameheadpos; but if we failed for any, we
     * must forcibly update aggregatedbase.
     */
    winstate->aggregatedbase = winstate->frameheadpos;

    /*
     * If we created a mark pointer for aggregates, keep it pushed up to frame
     * head, so that tuplestore can discard unnecessary rows.
     */
    if (agg_winobj->markptr >= 0)
        WinSetMarkPosition(agg_winobj, winstate->frameheadpos);

    /*
     * Now restart the aggregates that require it.
     *
     * We assume that aggregates using the shared context always restart if
     * *any* aggregate restarts, and we may thus clean up the shared
     * aggcontext if that is the case.  Private aggcontexts are reset by
     * initialize_windowaggregate() if their owning aggregate restarts. If we
     * aren't restarting an aggregate, we need to free any previously saved
     * result for it, else we'll leak memory.
     */
    if (numaggs_restart > 0)
        MemoryContextResetAndDeleteChildren(winstate->aggcontext);
    for (i = 0; i < numaggs; i++)
    {
        peraggstate = &winstate->peragg[i];

        /* Aggregates using the shared ctx must restart if *any* agg does */
        Assert(peraggstate->aggcontext != winstate->aggcontext ||
               numaggs_restart == 0 ||
               peraggstate->restart);

        if (peraggstate->restart)
        {
            wfuncno = peraggstate->wfuncno;
            initialize_windowaggregate(winstate,
                                       &winstate->perfunc[wfuncno],
                                       peraggstate);
        }
        else if (!peraggstate->resultValueIsNull)
        {
            if (!peraggstate->resulttypeByVal)
                pfree(DatumGetPointer(peraggstate->resultValue));
            peraggstate->resultValue = (Datum) 0;
            peraggstate->resultValueIsNull = true;
        }
    }

    /*
     * Non-restarted aggregates now contain the rows between aggregatedbase
     * (i.e., frameheadpos) and aggregatedupto, while restarted aggregates
     * contain no rows.  If there are any restarted aggregates, we must thus
     * begin aggregating anew at frameheadpos, otherwise we may simply
     * continue at aggregatedupto.  We must remember the old value of
     * aggregatedupto to know how long to skip advancing non-restarted
     * aggregates.  If we modify aggregatedupto, we must also clear
     * agg_row_slot, per the loop invariant below.
     */
    aggregatedupto_nonrestarted = winstate->aggregatedupto;
    if (numaggs_restart > 0 &&
        winstate->aggregatedupto != winstate->frameheadpos)
    {
        winstate->aggregatedupto = winstate->frameheadpos;
        ExecClearTuple(agg_row_slot);
    }

    /*
     * Advance until we reach a row not in frame (or end of partition).
     *
     * Note the loop invariant: agg_row_slot is either empty or holds the row
     * at position aggregatedupto.  We advance aggregatedupto after processing
     * a row.
     */
    for (;;)
    {
        int         ret;

        /* Fetch next row if we didn't already */
        if (TupIsNull(agg_row_slot))
        {
            if (!window_gettupleslot(agg_winobj, winstate->aggregatedupto,
                                     agg_row_slot))
                break;          /* must be end of partition */
        }

        /*
         * Exit loop if no more rows can be in frame.  Skip aggregation if
         * current row is not in frame but there might be more in the frame.
         */
        ret = row_is_in_frame(winstate, winstate->aggregatedupto, agg_row_slot);
        if (ret < 0)
            break;
        if (ret == 0)
            goto next_tuple;

        /* Set tuple context for evaluation of aggregate arguments */
        winstate->tmpcontext->ecxt_outertuple = agg_row_slot;

        /* Accumulate row into the aggregates */
        for (i = 0; i < numaggs; i++)
        {
            peraggstate = &winstate->peragg[i];

            /* Non-restarted aggs skip until aggregatedupto_nonrestarted */
            if (!peraggstate->restart &&
                winstate->aggregatedupto < aggregatedupto_nonrestarted)
                continue;

            wfuncno = peraggstate->wfuncno;
            advance_windowaggregate(winstate,
                                    &winstate->perfunc[wfuncno],
                                    peraggstate);
        }

next_tuple:
        /* Reset per-input-tuple context after each tuple */
        ResetExprContext(winstate->tmpcontext);

        /* And advance the aggregated-row state */
        winstate->aggregatedupto++;
        ExecClearTuple(agg_row_slot);
    }

    /* The frame's end is not supposed to move backwards, ever */
    Assert(aggregatedupto_nonrestarted <= winstate->aggregatedupto);

    /*
     * finalize aggregates and fill result/isnull fields.
     */
    for (i = 0; i < numaggs; i++)
    {
        Datum      *result;
        bool       *isnull;

        peraggstate = &winstate->peragg[i];
        wfuncno = peraggstate->wfuncno;
        result = &econtext->ecxt_aggvalues[wfuncno];
        isnull = &econtext->ecxt_aggnulls[wfuncno];
        finalize_windowaggregate(winstate,
                                 &winstate->perfunc[wfuncno],
                                 peraggstate,
                                 result, isnull);

        /*
         * save the result in case next row shares the same frame.
         *
         * XXX in some framing modes, eg ROWS/END_CURRENT_ROW, we can know in
         * advance that the next row can't possibly share the same frame. Is
         * it worth detecting that and skipping this code?
         */
        if (!peraggstate->resulttypeByVal && !*isnull)
        {
            oldContext = MemoryContextSwitchTo(peraggstate->aggcontext);
            peraggstate->resultValue =
                datumCopy(*result,
                          peraggstate->resulttypeByVal,
                          peraggstate->resulttypeLen);
            MemoryContextSwitchTo(oldContext);
        }
        else
        {
            peraggstate->resultValue = *result;
        }
        peraggstate->resultValueIsNull = *isnull;
    }
}

/*
 * eval_windowfunction
 *
 * Arguments of window functions are not evaluated here, because a window
 * function can need random access to arbitrary rows in the partition.
 * The window function uses the special WinGetFuncArgInPartition and
 * WinGetFuncArgInFrame functions to evaluate the arguments for the rows
 * it wants.
 */
static void
eval_windowfunction(WindowAggState *winstate, WindowStatePerFunc perfuncstate,
                    Datum *result, bool *isnull)
{
    LOCAL_FCINFO(fcinfo, FUNC_MAX_ARGS);
    MemoryContext oldContext;

    oldContext = MemoryContextSwitchTo(winstate->ss.ps.ps_ExprContext->ecxt_per_tuple_memory);

    /*
     * We don't pass any normal arguments to a window function, but we do pass
     * it the number of arguments, in order to permit window function
     * implementations to support varying numbers of arguments.  The real info
     * goes through the WindowObject, which is passed via fcinfo->context.
     */
    InitFunctionCallInfoData(*fcinfo, &(perfuncstate->flinfo),
                             perfuncstate->numArguments,
                             perfuncstate->winCollation,
                             (void *) perfuncstate->winobj, NULL);
    /* Just in case, make all the regular argument slots be null */
    for (int argno = 0; argno < perfuncstate->numArguments; argno++)
        fcinfo->args[argno].isnull = true;
    /* Window functions don't have a current aggregate context, either */
    winstate->curaggcontext = NULL;

    *result = FunctionCallInvoke(fcinfo);
    *isnull = fcinfo->isnull;

    /*
     * Make sure pass-by-ref data is allocated in the appropriate context. (We
     * need this in case the function returns a pointer into some short-lived
     * tuple, as is entirely possible.)
     */
    if (!perfuncstate->resulttypeByVal && !fcinfo->isnull &&
        !MemoryContextContains(CurrentMemoryContext,
                               DatumGetPointer(*result)))
        *result = datumCopy(*result,
                            perfuncstate->resulttypeByVal,
                            perfuncstate->resulttypeLen);

    MemoryContextSwitchTo(oldContext);
}

/*
 * begin_partition
 * Start buffering rows of the next partition.
 */
static void
begin_partition(WindowAggState *winstate)
{
    WindowAgg  *node = (WindowAgg *) winstate->ss.ps.plan;
    PlanState  *outerPlan = outerPlanState(winstate);
    int         frameOptions = winstate->frameOptions;
    int         numfuncs = winstate->numfuncs;
    int         i;

    winstate->partition_spooled = false;
    winstate->framehead_valid = false;
    winstate->frametail_valid = false;
    winstate->grouptail_valid = false;
    winstate->spooled_rows = 0;
    winstate->currentpos = 0;
    winstate->frameheadpos = 0;
    winstate->frametailpos = 0;
    winstate->currentgroup = 0;
    winstate->frameheadgroup = 0;
    winstate->frametailgroup = 0;
    winstate->groupheadpos = 0;
    winstate->grouptailpos = -1;    /* see update_grouptailpos */
    ExecClearTuple(winstate->agg_row_slot);
    if (winstate->framehead_slot)
        ExecClearTuple(winstate->framehead_slot);
    if (winstate->frametail_slot)
        ExecClearTuple(winstate->frametail_slot);

    /*
     * If this is the very first partition, we need to fetch the first input
     * row to store in first_part_slot.
     */
    if (TupIsNull(winstate->first_part_slot))
    {
        TupleTableSlot *outerslot = ExecProcNode(outerPlan);

        if (!TupIsNull(outerslot))
            ExecCopySlot(winstate->first_part_slot, outerslot);
        else
        {
            /* outer plan is empty, so we have nothing to do */
            winstate->partition_spooled = true;
            winstate->more_partitions = false;
            return;
        }
    }

    /* Create new tuplestore for this partition */
    winstate->buffer = tuplestore_begin_heap(false, false, work_mem);

    /*
     * Set up read pointers for the tuplestore.  The current pointer doesn't
     * need BACKWARD capability, but the per-window-function read pointers do,
     * and the aggregate pointer does if we might need to restart aggregation.
     */
    winstate->current_ptr = 0;  /* read pointer 0 is pre-allocated */

    /* reset default REWIND capability bit for current ptr */
    tuplestore_set_eflags(winstate->buffer, 0);

    /* create read pointers for aggregates, if needed */
    if (winstate->numaggs > 0)
    {
        WindowObject agg_winobj = winstate->agg_winobj;
        int         readptr_flags = 0;

        /*
         * If the frame head is potentially movable, or we have an EXCLUSION
         * clause, we might need to restart aggregation ...
         */
        if (!(frameOptions & FRAMEOPTION_START_UNBOUNDED_PRECEDING) ||
            (frameOptions & FRAMEOPTION_EXCLUSION))
        {
            /* ... so create a mark pointer to track the frame head */
            agg_winobj->markptr = tuplestore_alloc_read_pointer(winstate->buffer, 0);
            /* and the read pointer will need BACKWARD capability */
            readptr_flags |= EXEC_FLAG_BACKWARD;
        }

        agg_winobj->readptr = tuplestore_alloc_read_pointer(winstate->buffer,
                                                            readptr_flags);
        agg_winobj->markpos = -1;
        agg_winobj->seekpos = -1;

        /* Also reset the row counters for aggregates */
        winstate->aggregatedbase = 0;
        winstate->aggregatedupto = 0;
    }

    /* create mark and read pointers for each real window function */
    for (i = 0; i < numfuncs; i++)
    {
        WindowStatePerFunc perfuncstate = &(winstate->perfunc[i]);

        if (!perfuncstate->plain_agg)
        {
            WindowObject winobj = perfuncstate->winobj;

            winobj->markptr = tuplestore_alloc_read_pointer(winstate->buffer,
                                                            0);
            winobj->readptr = tuplestore_alloc_read_pointer(winstate->buffer,
                                                            EXEC_FLAG_BACKWARD);
            winobj->markpos = -1;
            winobj->seekpos = -1;
        }
    }

    /*
     * If we are in RANGE or GROUPS mode, then determining frame boundaries
     * requires physical access to the frame endpoint rows, except in certain
     * degenerate cases.  We create read pointers to point to those rows, to
     * simplify access and ensure that the tuplestore doesn't discard the
     * endpoint rows prematurely.  (Must create pointers in exactly the same
     * cases that update_frameheadpos and update_frametailpos need them.)
     */
    winstate->framehead_ptr = winstate->frametail_ptr = -1; /* if not used */

    if (frameOptions & (FRAMEOPTION_RANGE | FRAMEOPTION_GROUPS))
    {
        if (((frameOptions & FRAMEOPTION_START_CURRENT_ROW) &&
             node->ordNumCols != 0) ||
            (frameOptions & FRAMEOPTION_START_OFFSET))
            winstate->framehead_ptr =
                tuplestore_alloc_read_pointer(winstate->buffer, 0);
        if (((frameOptions & FRAMEOPTION_END_CURRENT_ROW) &&
             node->ordNumCols != 0) ||
            (frameOptions & FRAMEOPTION_END_OFFSET))
            winstate->frametail_ptr =
                tuplestore_alloc_read_pointer(winstate->buffer, 0);
    }

    /*
     * If we have an exclusion clause that requires knowing the boundaries of
     * the current row's peer group, we create a read pointer to track the
     * tail position of the peer group (i.e., first row of the next peer
     * group).  The head position does not require its own pointer because we
     * maintain that as a side effect of advancing the current row.
     */
    winstate->grouptail_ptr = -1;

    if ((frameOptions & (FRAMEOPTION_EXCLUDE_GROUP |
                         FRAMEOPTION_EXCLUDE_TIES)) &&
        node->ordNumCols != 0)
    {
        winstate->grouptail_ptr =
            tuplestore_alloc_read_pointer(winstate->buffer, 0);
    }

    /*
     * Store the first tuple into the tuplestore (it's always available now;
     * we either read it above, or saved it at the end of previous partition)
     */
    tuplestore_puttupleslot(winstate->buffer, winstate->first_part_slot);
    winstate->spooled_rows++;
}

/*
 * Read tuples from the outer node, up to and including position 'pos', and
 * store them into the tuplestore. If pos is -1, reads the whole partition.
 */
static void
spool_tuples(WindowAggState *winstate, int64 pos)
{
    WindowAgg  *node = (WindowAgg *) winstate->ss.ps.plan;
    PlanState  *outerPlan;
    TupleTableSlot *outerslot;
    MemoryContext oldcontext;

    if (!winstate->buffer)
        return;                 /* just a safety check */
    if (winstate->partition_spooled)
        return;                 /* whole partition done already */

    /*
     * If the tuplestore has spilled to disk, alternate reading and writing
     * becomes quite expensive due to frequent buffer flushes.  It's cheaper
     * to force the entire partition to get spooled in one go.
     *
     * XXX this is a horrid kluge --- it'd be better to fix the performance
     * problem inside tuplestore.  FIXME
     */
    if (!tuplestore_in_memory(winstate->buffer))
        pos = -1;

    outerPlan = outerPlanState(winstate);

    /* Must be in query context to call outerplan */
    oldcontext = MemoryContextSwitchTo(winstate->ss.ps.ps_ExprContext->ecxt_per_query_memory);

    while (winstate->spooled_rows <= pos || pos == -1)
    {
        outerslot = ExecProcNode(outerPlan);
        if (TupIsNull(outerslot))
        {
            /* reached the end of the last partition */
            winstate->partition_spooled = true;
            winstate->more_partitions = false;
            break;
        }

        if (node->partNumCols > 0)
        {
            ExprContext *econtext = winstate->tmpcontext;

            econtext->ecxt_innertuple = winstate->first_part_slot;
            econtext->ecxt_outertuple = outerslot;

            /* Check if this tuple still belongs to the current partition */
            if (!ExecQualAndReset(winstate->partEqfunction, econtext))
            {
                /*
                 * end of partition; copy the tuple for the next cycle.
                 */
                ExecCopySlot(winstate->first_part_slot, outerslot);
                winstate->partition_spooled = true;
                winstate->more_partitions = true;
                break;
            }
        }

        /* Still in partition, so save it into the tuplestore */
        tuplestore_puttupleslot(winstate->buffer, outerslot);
        winstate->spooled_rows++;
    }

    MemoryContextSwitchTo(oldcontext);
}

/*
 * release_partition
 * clear information kept within a partition, including
 * tuplestore and aggregate results.
 */
static void
release_partition(WindowAggState *winstate)
{
    int         i;

    for (i = 0; i < winstate->numfuncs; i++)
    {
        WindowStatePerFunc perfuncstate = &(winstate->perfunc[i]);

        /* Release any partition-local state of this window function */
        if (perfuncstate->winobj)
            perfuncstate->winobj->localmem = NULL;
    }

    /*
     * Release all partition-local memory (in particular, any partition-local
     * state that we might have trashed our pointers to in the above loop, and
     * any aggregate temp data).  We don't rely on retail pfree because some
     * aggregates might have allocated data we don't have direct pointers to.
     */
    MemoryContextResetAndDeleteChildren(winstate->partcontext);
    MemoryContextResetAndDeleteChildren(winstate->aggcontext);
    for (i = 0; i < winstate->numaggs; i++)
    {
        if (winstate->peragg[i].aggcontext != winstate->aggcontext)
            MemoryContextResetAndDeleteChildren(winstate->peragg[i].aggcontext);
    }

    if (winstate->buffer)
        tuplestore_end(winstate->buffer);
    winstate->buffer = NULL;
    winstate->partition_spooled = false;
}

/*
 * row_is_in_frame
 * Determine whether a row is in the current row's window frame according
 * to our window framing rule
 *
 * The caller must have already determined that the row is in the partition
 * and fetched it into a slot.  This function just encapsulates the framing
 * rules.
 *
 * Returns:
 * -1, if the row is out of frame and no succeeding rows can be in frame
 * 0, if the row is out of frame but succeeding rows might be in frame
 * 1, if the row is in frame
 *
 * May clobber winstate->temp_slot_2.
 */
static int
row_is_in_frame(WindowAggState *winstate, int64 pos, TupleTableSlot *slot)
{
    int         frameOptions = winstate->frameOptions;

    Assert(pos >= 0);           /* else caller error */

    /*
     * First, check frame starting conditions.  We might as well delegate this
     * to update_frameheadpos always; it doesn't add any notable cost.
     */
    update_frameheadpos(winstate);
    if (pos < winstate->frameheadpos)
        return 0;

    /*
     * Okay so far, now check frame ending conditions.  Here, we avoid calling
     * update_frametailpos in simple cases, so as not to spool tuples further
     * ahead than necessary.
     */
    if (frameOptions & FRAMEOPTION_END_CURRENT_ROW)
    {
        if (frameOptions & FRAMEOPTION_ROWS)
        {
            /* rows after current row are out of frame */
            if (pos > winstate->currentpos)
                return -1;
        }
        else if (frameOptions & (FRAMEOPTION_RANGE | FRAMEOPTION_GROUPS))
        {
            /* following row that is not peer is out of frame */
            if (pos > winstate->currentpos &&
                !are_peers(winstate, slot, winstate->ss.ss_ScanTupleSlot))
                return -1;
        }
        else
            Assert(false);
    }
    else if (frameOptions & FRAMEOPTION_END_OFFSET)
    {
        if (frameOptions & FRAMEOPTION_ROWS)
        {
            int64       offset = DatumGetInt64(winstate->endOffsetValue);

            /* rows after current row + offset are out of frame */
            if (frameOptions & FRAMEOPTION_END_OFFSET_PRECEDING)
                offset = -offset;

            if (pos > winstate->currentpos + offset)
                return -1;
        }
        else if (frameOptions & (FRAMEOPTION_RANGE | FRAMEOPTION_GROUPS))
        {
            /* hard cases, so delegate to update_frametailpos */
            update_frametailpos(winstate);
            if (pos >= winstate->frametailpos)
                return -1;
        }
        else
            Assert(false);
    }

    /* Check exclusion clause */
    if (frameOptions & FRAMEOPTION_EXCLUDE_CURRENT_ROW)
    {
        if (pos == winstate->currentpos)
            return 0;
    }
    else if ((frameOptions & FRAMEOPTION_EXCLUDE_GROUP) ||
             ((frameOptions & FRAMEOPTION_EXCLUDE_TIES) &&
              pos != winstate->currentpos))
    {
        WindowAgg  *node = (WindowAgg *) winstate->ss.ps.plan;

        /* If no ORDER BY, all rows are peers with each other */
        if (node->ordNumCols == 0)
            return 0;
        /* Otherwise, check the group boundaries */
        if (pos >= winstate->groupheadpos)
        {
            update_grouptailpos(winstate);
            if (pos < winstate->grouptailpos)
                return 0;
        }
    }

    /* If we get here, it's in frame */
    return 1;
}

/*
 * update_frameheadpos
 * make frameheadpos valid for the current row
 *
 * Note that frameheadpos is computed without regard for any window exclusion
 * clause; the current row and/or its peers are considered part of the frame
 * for this purpose even if they must be excluded later.
 *
 * May clobber winstate->temp_slot_2.
 */
static void
update_frameheadpos(WindowAggState *winstate)
{
    WindowAgg  *node = (WindowAgg *) winstate->ss.ps.plan;
    int         frameOptions = winstate->frameOptions;
    MemoryContext oldcontext;

    if (winstate->framehead_valid)
        return;                 /* already known for current row */

    /* We may be called in a short-lived context */
    oldcontext = MemoryContextSwitchTo(winstate->ss.ps.ps_ExprContext->ecxt_per_query_memory);

    if (frameOptions & FRAMEOPTION_START_UNBOUNDED_PRECEDING)
    {
        /* In UNBOUNDED PRECEDING mode, frame head is always row 0 */
        winstate->frameheadpos = 0;
        winstate->framehead_valid = true;
    }
    else if (frameOptions & FRAMEOPTION_START_CURRENT_ROW)
    {
        if (frameOptions & FRAMEOPTION_ROWS)
        {
            /* In ROWS mode, frame head is the same as current */
            winstate->frameheadpos = winstate->currentpos;
            winstate->framehead_valid = true;
        }
        else if (frameOptions & (FRAMEOPTION_RANGE | FRAMEOPTION_GROUPS))
        {
            /* If no ORDER BY, all rows are peers with each other */
            if (node->ordNumCols == 0)
            {
                winstate->frameheadpos = 0;
                winstate->framehead_valid = true;
                MemoryContextSwitchTo(oldcontext);
                return;
            }

            /*
             * In RANGE or GROUPS START_CURRENT_ROW mode, frame head is the
             * first row that is a peer of current row.  We keep a copy of the
             * last-known frame head row in framehead_slot, and advance as
             * necessary.  Note that if we reach end of partition, we will
             * leave frameheadpos = end+1 and framehead_slot empty.
             */
            tuplestore_select_read_pointer(winstate->buffer,
                                           winstate->framehead_ptr);
            if (winstate->frameheadpos == 0 &&
                TupIsNull(winstate->framehead_slot))
            {
                /* fetch first row into framehead_slot, if we didn't already */
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->framehead_slot))
                    elog(ERROR, "unexpected end of tuplestore");
            }

            while (!TupIsNull(winstate->framehead_slot))
            {
                if (are_peers(winstate, winstate->framehead_slot,
                              winstate->ss.ss_ScanTupleSlot))
                    break;      /* this row is the correct frame head */
                /* Note we advance frameheadpos even if the fetch fails */
                winstate->frameheadpos++;
                spool_tuples(winstate, winstate->frameheadpos);
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->framehead_slot))
                    break;      /* end of partition */
            }
            winstate->framehead_valid = true;
        }
        else
            Assert(false);
    }
    else if (frameOptions & FRAMEOPTION_START_OFFSET)
    {
        if (frameOptions & FRAMEOPTION_ROWS)
        {
            /* In ROWS mode, bound is physically n before/after current */
            int64       offset = DatumGetInt64(winstate->startOffsetValue);

            if (frameOptions & FRAMEOPTION_START_OFFSET_PRECEDING)
                offset = -offset;

            winstate->frameheadpos = winstate->currentpos + offset;
            /* frame head can't go before first row */
            if (winstate->frameheadpos < 0)
                winstate->frameheadpos = 0;
            else if (winstate->frameheadpos > winstate->currentpos + 1)
            {
                /* make sure frameheadpos is not past end of partition */
                spool_tuples(winstate, winstate->frameheadpos - 1);
                if (winstate->frameheadpos > winstate->spooled_rows)
                    winstate->frameheadpos = winstate->spooled_rows;
            }
            winstate->framehead_valid = true;
        }
        else if (frameOptions & FRAMEOPTION_RANGE)
        {
            /*
             * In RANGE START_OFFSET mode, frame head is the first row that
             * satisfies the in_range constraint relative to the current row.
             * We keep a copy of the last-known frame head row in
             * framehead_slot, and advance as necessary.  Note that if we
             * reach end of partition, we will leave frameheadpos = end+1 and
             * framehead_slot empty.
             */
            int         sortCol = node->ordColIdx[0];
            bool        sub,
                        less;

            /* We must have an ordering column */
            Assert(node->ordNumCols == 1);

            /* Precompute flags for in_range checks */
            if (frameOptions & FRAMEOPTION_START_OFFSET_PRECEDING)
                sub = true;     /* subtract startOffset from current row */
            else
                sub = false;    /* add it */
            less = false;       /* normally, we want frame head >= sum */
            /* If sort order is descending, flip both flags */
            if (!winstate->inRangeAsc)
            {
                sub = !sub;
                less = true;
            }

            tuplestore_select_read_pointer(winstate->buffer,
                                           winstate->framehead_ptr);
            if (winstate->frameheadpos == 0 &&
                TupIsNull(winstate->framehead_slot))
            {
                /* fetch first row into framehead_slot, if we didn't already */
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->framehead_slot))
                    elog(ERROR, "unexpected end of tuplestore");
            }

            while (!TupIsNull(winstate->framehead_slot))
            {
                Datum       headval,
                            currval;
                bool        headisnull,
                            currisnull;

                headval = slot_getattr(winstate->framehead_slot, sortCol,
                                       &headisnull);
                currval = slot_getattr(winstate->ss.ss_ScanTupleSlot, sortCol,
                                       &currisnull);
                if (headisnull || currisnull)
                {
                    /* order of the rows depends only on nulls_first */
                    if (winstate->inRangeNullsFirst)
                    {
                        /* advance head if head is null and curr is not */
                        if (!headisnull || currisnull)
                            break;
                    }
                    else
                    {
                        /* advance head if head is not null and curr is null */
                        if (headisnull || !currisnull)
                            break;
                    }
                }
                else
                {
                    if (DatumGetBool(FunctionCall5Coll(&winstate->startInRangeFunc,
                                                       winstate->inRangeColl,
                                                       headval,
                                                       currval,
                                                       winstate->startOffsetValue,
                                                       BoolGetDatum(sub),
                                                       BoolGetDatum(less))))
                        break;  /* this row is the correct frame head */
                }
                /* Note we advance frameheadpos even if the fetch fails */
                winstate->frameheadpos++;
                spool_tuples(winstate, winstate->frameheadpos);
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->framehead_slot))
                    break;      /* end of partition */
            }
            winstate->framehead_valid = true;
        }
        else if (frameOptions & FRAMEOPTION_GROUPS)
        {
            /*
             * In GROUPS START_OFFSET mode, frame head is the first row of the
             * first peer group whose number satisfies the offset constraint.
             * We keep a copy of the last-known frame head row in
             * framehead_slot, and advance as necessary.  Note that if we
             * reach end of partition, we will leave frameheadpos = end+1 and
             * framehead_slot empty.
             */
            int64       offset = DatumGetInt64(winstate->startOffsetValue);
            int64       minheadgroup;

            if (frameOptions & FRAMEOPTION_START_OFFSET_PRECEDING)
                minheadgroup = winstate->currentgroup - offset;
            else
                minheadgroup = winstate->currentgroup + offset;

            tuplestore_select_read_pointer(winstate->buffer,
                                           winstate->framehead_ptr);
            if (winstate->frameheadpos == 0 &&
                TupIsNull(winstate->framehead_slot))
            {
                /* fetch first row into framehead_slot, if we didn't already */
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->framehead_slot))
                    elog(ERROR, "unexpected end of tuplestore");
            }

            while (!TupIsNull(winstate->framehead_slot))
            {
                if (winstate->frameheadgroup >= minheadgroup)
                    break;      /* this row is the correct frame head */
                ExecCopySlot(winstate->temp_slot_2, winstate->framehead_slot);
                /* Note we advance frameheadpos even if the fetch fails */
                winstate->frameheadpos++;
                spool_tuples(winstate, winstate->frameheadpos);
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->framehead_slot))
                    break;      /* end of partition */
                if (!are_peers(winstate, winstate->temp_slot_2,
                               winstate->framehead_slot))
                    winstate->frameheadgroup++;
            }
            ExecClearTuple(winstate->temp_slot_2);
            winstate->framehead_valid = true;
        }
        else
            Assert(false);
    }
    else
        Assert(false);

    MemoryContextSwitchTo(oldcontext);
}

/*
 * update_frametailpos
 * make frametailpos valid for the current row
 *
 * Note that frametailpos is computed without regard for any window exclusion
 * clause; the current row and/or its peers are considered part of the frame
 * for this purpose even if they must be excluded later.
 *
 * May clobber winstate->temp_slot_2.
 */
static void
update_frametailpos(WindowAggState *winstate)
{
    WindowAgg  *node = (WindowAgg *) winstate->ss.ps.plan;
    int         frameOptions = winstate->frameOptions;
    MemoryContext oldcontext;

    if (winstate->frametail_valid)
        return;                 /* already known for current row */

    /* We may be called in a short-lived context */
    oldcontext = MemoryContextSwitchTo(winstate->ss.ps.ps_ExprContext->ecxt_per_query_memory);

    if (frameOptions & FRAMEOPTION_END_UNBOUNDED_FOLLOWING)
    {
        /* In UNBOUNDED FOLLOWING mode, all partition rows are in frame */
        spool_tuples(winstate, -1);
        winstate->frametailpos = winstate->spooled_rows;
        winstate->frametail_valid = true;
    }
    else if (frameOptions & FRAMEOPTION_END_CURRENT_ROW)
    {
        if (frameOptions & FRAMEOPTION_ROWS)
        {
            /* In ROWS mode, exactly the rows up to current are in frame */
            winstate->frametailpos = winstate->currentpos + 1;
            winstate->frametail_valid = true;
        }
        else if (frameOptions & (FRAMEOPTION_RANGE | FRAMEOPTION_GROUPS))
        {
            /* If no ORDER BY, all rows are peers with each other */
            if (node->ordNumCols == 0)
            {
                spool_tuples(winstate, -1);
                winstate->frametailpos = winstate->spooled_rows;
                winstate->frametail_valid = true;
                MemoryContextSwitchTo(oldcontext);
                return;
            }

            /*
             * In RANGE or GROUPS END_CURRENT_ROW mode, frame end is the last
             * row that is a peer of current row, frame tail is the row after
             * that (if any).  We keep a copy of the last-known frame tail row
             * in frametail_slot, and advance as necessary.  Note that if we
             * reach end of partition, we will leave frametailpos = end+1 and
             * frametail_slot empty.
             */
            tuplestore_select_read_pointer(winstate->buffer,
                                           winstate->frametail_ptr);
            if (winstate->frametailpos == 0 &&
                TupIsNull(winstate->frametail_slot))
            {
                /* fetch first row into frametail_slot, if we didn't already */
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->frametail_slot))
                    elog(ERROR, "unexpected end of tuplestore");
            }

            while (!TupIsNull(winstate->frametail_slot))
            {
                if (winstate->frametailpos > winstate->currentpos &&
                    !are_peers(winstate, winstate->frametail_slot,
                               winstate->ss.ss_ScanTupleSlot))
                    break;      /* this row is the frame tail */
                /* Note we advance frametailpos even if the fetch fails */
                winstate->frametailpos++;
                spool_tuples(winstate, winstate->frametailpos);
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->frametail_slot))
                    break;      /* end of partition */
            }
            winstate->frametail_valid = true;
        }
        else
            Assert(false);
    }
    else if (frameOptions & FRAMEOPTION_END_OFFSET)
    {
        if (frameOptions & FRAMEOPTION_ROWS)
        {
            /* In ROWS mode, bound is physically n before/after current */
            int64       offset = DatumGetInt64(winstate->endOffsetValue);

            if (frameOptions & FRAMEOPTION_END_OFFSET_PRECEDING)
                offset = -offset;

            winstate->frametailpos = winstate->currentpos + offset + 1;
            /* smallest allowable value of frametailpos is 0 */
            if (winstate->frametailpos < 0)
                winstate->frametailpos = 0;
            else if (winstate->frametailpos > winstate->currentpos + 1)
            {
                /* make sure frametailpos is not past end of partition */
                spool_tuples(winstate, winstate->frametailpos - 1);
                if (winstate->frametailpos > winstate->spooled_rows)
                    winstate->frametailpos = winstate->spooled_rows;
            }
            winstate->frametail_valid = true;
        }
        else if (frameOptions & FRAMEOPTION_RANGE)
        {
            /*
             * In RANGE END_OFFSET mode, frame end is the last row that
             * satisfies the in_range constraint relative to the current row,
             * frame tail is the row after that (if any).  We keep a copy of
             * the last-known frame tail row in frametail_slot, and advance as
             * necessary.  Note that if we reach end of partition, we will
             * leave frametailpos = end+1 and frametail_slot empty.
             */
            int         sortCol = node->ordColIdx[0];
            bool        sub,
                        less;

            /* We must have an ordering column */
            Assert(node->ordNumCols == 1);

            /* Precompute flags for in_range checks */
            if (frameOptions & FRAMEOPTION_END_OFFSET_PRECEDING)
                sub = true;     /* subtract endOffset from current row */
            else
                sub = false;    /* add it */
            less = true;        /* normally, we want frame tail <= sum */
            /* If sort order is descending, flip both flags */
            if (!winstate->inRangeAsc)
            {
                sub = !sub;
                less = false;
            }

            tuplestore_select_read_pointer(winstate->buffer,
                                           winstate->frametail_ptr);
            if (winstate->frametailpos == 0 &&
                TupIsNull(winstate->frametail_slot))
            {
                /* fetch first row into frametail_slot, if we didn't already */
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->frametail_slot))
                    elog(ERROR, "unexpected end of tuplestore");
            }

            while (!TupIsNull(winstate->frametail_slot))
            {
                Datum       tailval,
                            currval;
                bool        tailisnull,
                            currisnull;

                tailval = slot_getattr(winstate->frametail_slot, sortCol,
                                       &tailisnull);
                currval = slot_getattr(winstate->ss.ss_ScanTupleSlot, sortCol,
                                       &currisnull);
                if (tailisnull || currisnull)
                {
                    /* order of the rows depends only on nulls_first */
                    if (winstate->inRangeNullsFirst)
                    {
                        /* advance tail if tail is null or curr is not */
                        if (!tailisnull)
                            break;
                    }
                    else
                    {
                        /* advance tail if tail is not null or curr is null */
                        if (!currisnull)
                            break;
                    }
                }
                else
                {
                    if (!DatumGetBool(FunctionCall5Coll(&winstate->endInRangeFunc,
                                                        winstate->inRangeColl,
                                                        tailval,
                                                        currval,
                                                        winstate->endOffsetValue,
                                                        BoolGetDatum(sub),
                                                        BoolGetDatum(less))))
                        break;  /* this row is the correct frame tail */
                }
                /* Note we advance frametailpos even if the fetch fails */
                winstate->frametailpos++;
                spool_tuples(winstate, winstate->frametailpos);
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->frametail_slot))
                    break;      /* end of partition */
            }
            winstate->frametail_valid = true;
        }
        else if (frameOptions & FRAMEOPTION_GROUPS)
        {
            /*
             * In GROUPS END_OFFSET mode, frame end is the last row of the
             * last peer group whose number satisfies the offset constraint,
             * and frame tail is the row after that (if any).  We keep a copy
             * of the last-known frame tail row in frametail_slot, and advance
             * as necessary.  Note that if we reach end of partition, we will
             * leave frametailpos = end+1 and frametail_slot empty.
             */
            int64       offset = DatumGetInt64(winstate->endOffsetValue);
            int64       maxtailgroup;

            if (frameOptions & FRAMEOPTION_END_OFFSET_PRECEDING)
                maxtailgroup = winstate->currentgroup - offset;
            else
                maxtailgroup = winstate->currentgroup + offset;

            tuplestore_select_read_pointer(winstate->buffer,
                                           winstate->frametail_ptr);
            if (winstate->frametailpos == 0 &&
                TupIsNull(winstate->frametail_slot))
            {
                /* fetch first row into frametail_slot, if we didn't already */
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->frametail_slot))
                    elog(ERROR, "unexpected end of tuplestore");
            }

            while (!TupIsNull(winstate->frametail_slot))
            {
                if (winstate->frametailgroup > maxtailgroup)
                    break;      /* this row is the correct frame tail */
                ExecCopySlot(winstate->temp_slot_2, winstate->frametail_slot);
                /* Note we advance frametailpos even if the fetch fails */
                winstate->frametailpos++;
                spool_tuples(winstate, winstate->frametailpos);
                if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                             winstate->frametail_slot))
                    break;      /* end of partition */
                if (!are_peers(winstate, winstate->temp_slot_2,
                               winstate->frametail_slot))
                    winstate->frametailgroup++;
            }
            ExecClearTuple(winstate->temp_slot_2);
            winstate->frametail_valid = true;
        }
        else
            Assert(false);
    }
    else
        Assert(false);

    MemoryContextSwitchTo(oldcontext);
}

/*
 * update_grouptailpos
 * make grouptailpos valid for the current row
 *
 * May clobber winstate->temp_slot_2.
 */
static void
update_grouptailpos(WindowAggState *winstate)
{
    WindowAgg  *node = (WindowAgg *) winstate->ss.ps.plan;
    MemoryContext oldcontext;

    if (winstate->grouptail_valid)
        return;                 /* already known for current row */

    /* We may be called in a short-lived context */
    oldcontext = MemoryContextSwitchTo(winstate->ss.ps.ps_ExprContext->ecxt_per_query_memory);

    /* If no ORDER BY, all rows are peers with each other */
    if (node->ordNumCols == 0)
    {
        spool_tuples(winstate, -1);
        winstate->grouptailpos = winstate->spooled_rows;
        winstate->grouptail_valid = true;
        MemoryContextSwitchTo(oldcontext);
        return;
    }

    /*
     * Because grouptail_valid is reset only when current row advances into a
     * new peer group, we always reach here knowing that grouptailpos needs to
     * be advanced by at least one row.  Hence, unlike the otherwise similar
     * case for frame tail tracking, we do not need persistent storage of the
     * group tail row.
     */
    Assert(winstate->grouptailpos <= winstate->currentpos);
    tuplestore_select_read_pointer(winstate->buffer,
                                   winstate->grouptail_ptr);
    for (;;)
    {
        /* Note we advance grouptailpos even if the fetch fails */
        winstate->grouptailpos++;
        spool_tuples(winstate, winstate->grouptailpos);
        if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                     winstate->temp_slot_2))
            break;              /* end of partition */
        if (winstate->grouptailpos > winstate->currentpos &&
            !are_peers(winstate, winstate->temp_slot_2,
                       winstate->ss.ss_ScanTupleSlot))
            break;              /* this row is the group tail */
    }
    ExecClearTuple(winstate->temp_slot_2);
    winstate->grouptail_valid = true;

    MemoryContextSwitchTo(oldcontext);
}


/* -----------------
 * ExecWindowAgg
 *
 *  ExecWindowAgg receives tuples from its outer subplan and
 *  stores them into a tuplestore, then processes window functions.
 *  This node doesn't reduce nor qualify any row so the number of
 *  returned rows is exactly the same as its outer subplan's result.
 * -----------------
 */
static TupleTableSlot *
ExecWindowAgg(PlanState *pstate)
{
    WindowAggState *winstate = castNode(WindowAggState, pstate);
    ExprContext *econtext;
    int         i;
    int         numfuncs;

    CHECK_FOR_INTERRUPTS();

    if (winstate->all_done)
        return NULL;

    /*
     * Compute frame offset values, if any, during first call (or after a
     * rescan).  These are assumed to hold constant throughout the scan; if
     * user gives us a volatile expression, we'll only use its initial value.
     */
    if (winstate->all_first)
    {
        int         frameOptions = winstate->frameOptions;
        ExprContext *econtext = winstate->ss.ps.ps_ExprContext;
        Datum       value;
        bool        isnull;
        int16       len;
        bool        byval;

        if (frameOptions & FRAMEOPTION_START_OFFSET)
        {
            Assert(winstate->startOffset != NULL);
            value = ExecEvalExprSwitchContext(winstate->startOffset,
                                              econtext,
                                              &isnull);
            if (isnull)
                ereport(ERROR,
                        (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                         errmsg("frame starting offset must not be null")));
            /* copy value into query-lifespan context */
            get_typlenbyval(exprType((Node *) winstate->startOffset->expr),
                            &len, &byval);
            winstate->startOffsetValue = datumCopy(value, byval, len);
            if (frameOptions & (FRAMEOPTION_ROWS | FRAMEOPTION_GROUPS))
            {
                /* value is known to be int8 */
                int64       offset = DatumGetInt64(value);

                if (offset < 0)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_PRECEDING_OR_FOLLOWING_SIZE),
                             errmsg("frame starting offset must not be negative")));
            }
        }
        if (frameOptions & FRAMEOPTION_END_OFFSET)
        {
            Assert(winstate->endOffset != NULL);
            value = ExecEvalExprSwitchContext(winstate->endOffset,
                                              econtext,
                                              &isnull);
            if (isnull)
                ereport(ERROR,
                        (errcode(ERRCODE_NULL_VALUE_NOT_ALLOWED),
                         errmsg("frame ending offset must not be null")));
            /* copy value into query-lifespan context */
            get_typlenbyval(exprType((Node *) winstate->endOffset->expr),
                            &len, &byval);
            winstate->endOffsetValue = datumCopy(value, byval, len);
            if (frameOptions & (FRAMEOPTION_ROWS | FRAMEOPTION_GROUPS))
            {
                /* value is known to be int8 */
                int64       offset = DatumGetInt64(value);

                if (offset < 0)
                    ereport(ERROR,
                            (errcode(ERRCODE_INVALID_PRECEDING_OR_FOLLOWING_SIZE),
                             errmsg("frame ending offset must not be negative")));
            }
        }
        winstate->all_first = false;
    }

    if (winstate->buffer == NULL)
    {
        /* Initialize for first partition and set current row = 0 */
        begin_partition(winstate);
        /* If there are no input rows, we'll detect that and exit below */
    }
    else
    {
        /* Advance current row within partition */
        winstate->currentpos++;
        /* This might mean that the frame moves, too */
        winstate->framehead_valid = false;
        winstate->frametail_valid = false;
        /* we don't need to invalidate grouptail here; see below */
    }

    /*
     * Spool all tuples up to and including the current row, if we haven't
     * already
     */
    spool_tuples(winstate, winstate->currentpos);

    /* Move to the next partition if we reached the end of this partition */
    if (winstate->partition_spooled &&
        winstate->currentpos >= winstate->spooled_rows)
    {
        release_partition(winstate);

        if (winstate->more_partitions)
        {
            begin_partition(winstate);
            Assert(winstate->spooled_rows > 0);
        }
        else
        {
            winstate->all_done = true;
            return NULL;
        }
    }

    /* final output execution is in ps_ExprContext */
    econtext = winstate->ss.ps.ps_ExprContext;

    /* Clear the per-output-tuple context for current row */
    ResetExprContext(econtext);

    /*
     * Read the current row from the tuplestore, and save in ScanTupleSlot.
     * (We can't rely on the outerplan's output slot because we may have to
     * read beyond the current row.  Also, we have to actually copy the row
     * out of the tuplestore, since window function evaluation might cause the
     * tuplestore to dump its state to disk.)
     *
     * In GROUPS mode, or when tracking a group-oriented exclusion clause, we
     * must also detect entering a new peer group and update associated state
     * when that happens.  We use temp_slot_2 to temporarily hold the previous
     * row for this purpose.
     *
     * Current row must be in the tuplestore, since we spooled it above.
     */
    tuplestore_select_read_pointer(winstate->buffer, winstate->current_ptr);
    if ((winstate->frameOptions & (FRAMEOPTION_GROUPS |
                                   FRAMEOPTION_EXCLUDE_GROUP |
                                   FRAMEOPTION_EXCLUDE_TIES)) &&
        winstate->currentpos > 0)
    {
        ExecCopySlot(winstate->temp_slot_2, winstate->ss.ss_ScanTupleSlot);
        if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                     winstate->ss.ss_ScanTupleSlot))
            elog(ERROR, "unexpected end of tuplestore");
        if (!are_peers(winstate, winstate->temp_slot_2,
                       winstate->ss.ss_ScanTupleSlot))
        {
            winstate->currentgroup++;
            winstate->groupheadpos = winstate->currentpos;
            winstate->grouptail_valid = false;
        }
        ExecClearTuple(winstate->temp_slot_2);
    }
    else
    {
        if (!tuplestore_gettupleslot(winstate->buffer, true, true,
                                     winstate->ss.ss_ScanTupleSlot))
            elog(ERROR, "unexpected end of tuplestore");
    }

    /*
     * Evaluate true window functions
     */
    numfuncs = winstate->numfuncs;
    for (i = 0; i < numfuncs; i++)
    {
        WindowStatePerFunc perfuncstate = &(winstate->perfunc[i]);

        if (perfuncstate->plain_agg)
            continue;
        eval_windowfunction(winstate, perfuncstate,
                            &(econtext->ecxt_aggvalues[perfuncstate->wfuncstate->wfuncno]),
                            &(econtext->ecxt_aggnulls[perfuncstate->wfuncstate->wfuncno]));
    }

    /*
     * Evaluate aggregates
     */
    if (winstate->numaggs > 0)
        eval_windowaggregates(winstate);

    /*
     * If we have created auxiliary read pointers for the frame or group
     * boundaries, force them to be kept up-to-date, because we don't know
     * whether the window function(s) will do anything that requires that.
     * Failing to advance the pointers would result in being unable to trim
     * data from the tuplestore, which is bad.  (If we could know in advance
     * whether the window functions will use frame boundary info, we could
     * skip creating these pointers in the first place ... but unfortunately
     * the window function API doesn't require that.)
     */
    if (winstate->framehead_ptr >= 0)
        update_frameheadpos(winstate);
    if (winstate->frametail_ptr >= 0)
        update_frametailpos(winstate);
    if (winstate->grouptail_ptr >= 0)
        update_grouptailpos(winstate);

    /*
     * Truncate any no-longer-needed rows from the tuplestore.
     */
    tuplestore_trim(winstate->buffer);

    /*
     * Form and return a projection tuple using the windowfunc results and the
     * current row.  Setting ecxt_outertuple arranges that any Vars will be
     * evaluated with respect to that row.
     */
    econtext->ecxt_outertuple = winstate->ss.ss_ScanTupleSlot;

    return ExecProject(winstate->ss.ps.ps_ProjInfo);
}

/* -----------------
 * ExecInitWindowAgg
 *
 *  Creates the run-time information for the WindowAgg node produced by the
 *  planner and initializes its outer subtree
 * -----------------
 */
WindowAggState *
ExecInitWindowAgg(WindowAgg *node, EState *estate, int eflags)
{
    WindowAggState *winstate;
    Plan       *outerPlan;
    ExprContext *econtext;
    ExprContext *tmpcontext;
    WindowStatePerFunc perfunc;
    WindowStatePerAgg peragg;
    int         frameOptions = node->frameOptions;
    int         numfuncs,
                wfuncno,
                numaggs,
                aggno;
    TupleDesc   scanDesc;
    ListCell   *l;

    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));

    /*
     * create state structure
     */
    winstate = makeNode(WindowAggState);
    winstate->ss.ps.plan = (Plan *) node;
    winstate->ss.ps.state = estate;
    winstate->ss.ps.ExecProcNode = ExecWindowAgg;

    /*
     * Create expression contexts.  We need two, one for per-input-tuple
     * processing and one for per-output-tuple processing.  We cheat a little
     * by using ExecAssignExprContext() to build both.
     */
    ExecAssignExprContext(estate, &winstate->ss.ps);
    tmpcontext = winstate->ss.ps.ps_ExprContext;
    winstate->tmpcontext = tmpcontext;
    ExecAssignExprContext(estate, &winstate->ss.ps);

    /* Create long-lived context for storage of partition-local memory etc */
    winstate->partcontext =
        AllocSetContextCreate(CurrentMemoryContext,
                              "WindowAgg Partition",
                              ALLOCSET_DEFAULT_SIZES);

    /*
     * Create mid-lived context for aggregate trans values etc.
     *
     * Note that moving aggregates each use their own private context, not
     * this one.
     */
    winstate->aggcontext =
        AllocSetContextCreate(CurrentMemoryContext,
                              "WindowAgg Aggregates",
                              ALLOCSET_DEFAULT_SIZES);

    /*
     * WindowAgg nodes never have quals, since they can only occur at the
     * logical top level of a query (ie, after any WHERE or HAVING filters)
     */
    Assert(node->plan.qual == NIL);
    winstate->ss.ps.qual = NULL;

    /*
     * initialize child nodes
     */
    outerPlan = outerPlan(node);
    outerPlanState(winstate) = ExecInitNode(outerPlan, estate, eflags);

    /*
     * initialize source tuple type (which is also the tuple type that we'll
     * store in the tuplestore and use in all our working slots).
     */
    ExecCreateScanSlotFromOuterPlan(estate, &winstate->ss, &TTSOpsMinimalTuple);
    scanDesc = winstate->ss.ss_ScanTupleSlot->tts_tupleDescriptor;

    /* the outer tuple isn't the child's tuple, but always a minimal tuple */
    winstate->ss.ps.outeropsset = true;
    winstate->ss.ps.outerops = &TTSOpsMinimalTuple;
    winstate->ss.ps.outeropsfixed = true;

    /*
     * tuple table initialization
     */
    winstate->first_part_slot = ExecInitExtraTupleSlot(estate, scanDesc,
                                                       &TTSOpsMinimalTuple);
    winstate->agg_row_slot = ExecInitExtraTupleSlot(estate, scanDesc,
                                                    &TTSOpsMinimalTuple);
    winstate->temp_slot_1 = ExecInitExtraTupleSlot(estate, scanDesc,
                                                   &TTSOpsMinimalTuple);
    winstate->temp_slot_2 = ExecInitExtraTupleSlot(estate, scanDesc,
                                                   &TTSOpsMinimalTuple);

    /*
     * create frame head and tail slots only if needed (must create slots in
     * exactly the same cases that update_frameheadpos and update_frametailpos
     * need them)
     */
    winstate->framehead_slot = winstate->frametail_slot = NULL;

    if (frameOptions & (FRAMEOPTION_RANGE | FRAMEOPTION_GROUPS))
    {
        if (((frameOptions & FRAMEOPTION_START_CURRENT_ROW) &&
             node->ordNumCols != 0) ||
            (frameOptions & FRAMEOPTION_START_OFFSET))
            winstate->framehead_slot = ExecInitExtraTupleSlot(estate, scanDesc,
                                                              &TTSOpsMinimalTuple);
        if (((frameOptions & FRAMEOPTION_END_CURRENT_ROW) &&
             node->ordNumCols != 0) ||
            (frameOptions & FRAMEOPTION_END_OFFSET))
            winstate->frametail_slot = ExecInitExtraTupleSlot(estate, scanDesc,
                                                              &TTSOpsMinimalTuple);
    }

    /*
     * Initialize result slot, type and projection.
     */
    ExecInitResultTupleSlotTL(&winstate->ss.ps, &TTSOpsVirtual);
    ExecAssignProjectionInfo(&winstate->ss.ps, NULL);

    /* Set up data for comparing tuples */
    if (node->partNumCols > 0)
        winstate->partEqfunction =
            execTuplesMatchPrepare(scanDesc,
                                   node->partNumCols,
                                   node->partColIdx,
                                   node->partOperators,
                                   node->partCollations,
                                   &winstate->ss.ps);

    if (node->ordNumCols > 0)
        winstate->ordEqfunction =
            execTuplesMatchPrepare(scanDesc,
                                   node->ordNumCols,
                                   node->ordColIdx,
                                   node->ordOperators,
                                   node->ordCollations,
                                   &winstate->ss.ps);

    /*
     * WindowAgg nodes use aggvalues and aggnulls as well as Agg nodes.
     */
    numfuncs = winstate->numfuncs;
    numaggs = winstate->numaggs;
    econtext = winstate->ss.ps.ps_ExprContext;
    econtext->ecxt_aggvalues = (Datum *) palloc0(sizeof(Datum) * numfuncs);
    econtext->ecxt_aggnulls = (bool *) palloc0(sizeof(bool) * numfuncs);

    /*
     * allocate per-wfunc/per-agg state information.
     */
    perfunc = (WindowStatePerFunc) palloc0(sizeof(WindowStatePerFuncData) * numfuncs);
    peragg = (WindowStatePerAgg) palloc0(sizeof(WindowStatePerAggData) * numaggs);
    winstate->perfunc = perfunc;
    winstate->peragg = peragg;

    wfuncno = -1;
    aggno = -1;
    foreach(l, winstate->funcs)
    {
        WindowFuncExprState *wfuncstate = (WindowFuncExprState *) lfirst(l);
        WindowFunc *wfunc = wfuncstate->wfunc;
        WindowStatePerFunc perfuncstate;
        AclResult   aclresult;
        int         i;

        if (wfunc->winref != node->winref)  /* planner screwed up? */
            elog(ERROR, "WindowFunc with winref %u assigned to WindowAgg with winref %u",
                 wfunc->winref, node->winref);

        /* Look for a previous duplicate window function */
        for (i = 0; i <= wfuncno; i++)
        {
            if (equal(wfunc, perfunc[i].wfunc) &&
                !contain_volatile_functions((Node *) wfunc))
                break;
        }
        if (i <= wfuncno)
        {
            /* Found a match to an existing entry, so just mark it */
            wfuncstate->wfuncno = i;
            continue;
        }

        /* Nope, so assign a new PerAgg record */
        perfuncstate = &perfunc[++wfuncno];

        /* Mark WindowFunc state node with assigned index in the result array */
        wfuncstate->wfuncno = wfuncno;

        /* Check permission to call window function */
        aclresult = pg_proc_aclcheck(wfunc->winfnoid, GetUserId(),
                                     ACL_EXECUTE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, OBJECT_FUNCTION,
                           get_func_name(wfunc->winfnoid));
        InvokeFunctionExecuteHook(wfunc->winfnoid);

        /* Fill in the perfuncstate data */
        perfuncstate->wfuncstate = wfuncstate;
        perfuncstate->wfunc = wfunc;
        perfuncstate->numArguments = list_length(wfuncstate->args);
        perfuncstate->winCollation = wfunc->inputcollid;

        get_typlenbyval(wfunc->wintype,
                        &perfuncstate->resulttypeLen,
                        &perfuncstate->resulttypeByVal);

        /*
         * If it's really just a plain aggregate function, we'll emulate the
         * Agg environment for it.
         */
        perfuncstate->plain_agg = wfunc->winagg;
        if (wfunc->winagg)
        {
            WindowStatePerAgg peraggstate;

            perfuncstate->aggno = ++aggno;
            peraggstate = &winstate->peragg[aggno];
            initialize_peragg(winstate, wfunc, peraggstate);
            peraggstate->wfuncno = wfuncno;
        }
        else
        {
            WindowObject winobj = makeNode(WindowObjectData);

            winobj->winstate = winstate;
            winobj->argstates = wfuncstate->args;
            winobj->localmem = NULL;
            perfuncstate->winobj = winobj;

            /* It's a real window function, so set up to call it. */
            fmgr_info_cxt(wfunc->winfnoid, &perfuncstate->flinfo,
                          econtext->ecxt_per_query_memory);
            fmgr_info_set_expr((Node *) wfunc, &perfuncstate->flinfo);
        }
    }

    /* Update numfuncs, numaggs to match number of unique functions found */
    winstate->numfuncs = wfuncno + 1;
    winstate->numaggs = aggno + 1;

    /* Set up WindowObject for aggregates, if needed */
    if (winstate->numaggs > 0)
    {
        WindowObject agg_winobj = makeNode(WindowObjectData);

        agg_winobj->winstate = winstate;
        agg_winobj->argstates = NIL;
        agg_winobj->localmem = NULL;
        /* make sure markptr = -1 to invalidate. It may not get used */
        agg_winobj->markptr = -1;
        agg_winobj->readptr = -1;
        winstate->agg_winobj = agg_winobj;
    }

    /* copy frame options to state node for easy access */
    winstate->frameOptions = frameOptions;

    /* initialize frame bound offset expressions */
    winstate->startOffset = ExecInitExpr((Expr *) node->startOffset,
                                         (PlanState *) winstate);
    winstate->endOffset = ExecInitExpr((Expr *) node->endOffset,
                                       (PlanState *) winstate);

    /* Lookup in_range support functions if needed */
    if (OidIsValid(node->startInRangeFunc))
        fmgr_info(node->startInRangeFunc, &winstate->startInRangeFunc);
    if (OidIsValid(node->endInRangeFunc))
        fmgr_info(node->endInRangeFunc, &winstate->endInRangeFunc);
    winstate->inRangeColl = node->inRangeColl;
    winstate->inRangeAsc = node->inRangeAsc;
    winstate->inRangeNullsFirst = node->inRangeNullsFirst;

    winstate->all_first = true;
    winstate->partition_spooled = false;
    winstate->more_partitions = false;

    return winstate;
}

/* -----------------
 * ExecEndWindowAgg
 * -----------------
 */
void
ExecEndWindowAgg(WindowAggState *node)
{
    PlanState  *outerPlan;
    int         i;

    release_partition(node);

    ExecClearTuple(node->ss.ss_ScanTupleSlot);
    ExecClearTuple(node->first_part_slot);
    ExecClearTuple(node->agg_row_slot);
    ExecClearTuple(node->temp_slot_1);
    ExecClearTuple(node->temp_slot_2);
    if (node->framehead_slot)
        ExecClearTuple(node->framehead_slot);
    if (node->frametail_slot)
        ExecClearTuple(node->frametail_slot);

    /*
     * Free both the expr contexts.
     */
    ExecFreeExprContext(&node->ss.ps);
    node->ss.ps.ps_ExprContext = node->tmpcontext;
    ExecFreeExprContext(&node->ss.ps);

    for (i = 0; i < node->numaggs; i++)
    {
        if (node->peragg[i].aggcontext != node->aggcontext)
            MemoryContextDelete(node->peragg[i].aggcontext);
    }
    MemoryContextDelete(node->partcontext);
    MemoryContextDelete(node->aggcontext);

    pfree(node->perfunc);
    pfree(node->peragg);

    outerPlan = outerPlanState(node);
    ExecEndNode(outerPlan);
}

/* -----------------
 * ExecReScanWindowAgg
 * -----------------
 */
void
ExecReScanWindowAgg(WindowAggState *node)
{
    PlanState  *outerPlan = outerPlanState(node);
    ExprContext *econtext = node->ss.ps.ps_ExprContext;

    node->all_done = false;
    node->all_first = true;

    /* release tuplestore et al */
    release_partition(node);

    /* release all temp tuples, but especially first_part_slot */
    ExecClearTuple(node->ss.ss_ScanTupleSlot);
    ExecClearTuple(node->first_part_slot);
    ExecClearTuple(node->agg_row_slot);
    ExecClearTuple(node->temp_slot_1);
    ExecClearTuple(node->temp_slot_2);
    if (node->framehead_slot)
        ExecClearTuple(node->framehead_slot);
    if (node->frametail_slot)
        ExecClearTuple(node->frametail_slot);

    /* Forget current wfunc values */
    MemSet(econtext->ecxt_aggvalues, 0, sizeof(Datum) * node->numfuncs);
    MemSet(econtext->ecxt_aggnulls, 0, sizeof(bool) * node->numfuncs);

    /*
     * if chgParam of subnode is not null then plan will be re-scanned by
     * first ExecProcNode.
     */
    if (outerPlan->chgParam == NULL)
        ExecReScan(outerPlan);
}

/*
 * initialize_peragg
 *
 * Almost same as in nodeAgg.c, except we don't support DISTINCT currently.
 */
static WindowStatePerAggData *
initialize_peragg(WindowAggState *winstate, WindowFunc *wfunc,
                  WindowStatePerAgg peraggstate)
{
    Oid         inputTypes[FUNC_MAX_ARGS];
    int         numArguments;
    HeapTuple   aggTuple;
    Form_pg_aggregate aggform;
    Oid         aggtranstype;
    AttrNumber  initvalAttNo;
    AclResult   aclresult;
    bool        use_ma_code;
    Oid         transfn_oid,
                invtransfn_oid,
                finalfn_oid;
    bool        finalextra;
    char        finalmodify;
    Expr       *transfnexpr,
               *invtransfnexpr,
               *finalfnexpr;
    Datum       textInitVal;
    int         i;
    ListCell   *lc;

    numArguments = list_length(wfunc->args);

    i = 0;
    foreach(lc, wfunc->args)
    {
        inputTypes[i++] = exprType((Node *) lfirst(lc));
    }

    aggTuple = SearchSysCache1(AGGFNOID, ObjectIdGetDatum(wfunc->winfnoid));
    if (!HeapTupleIsValid(aggTuple))
        elog(ERROR, "cache lookup failed for aggregate %u",
             wfunc->winfnoid);
    aggform = (Form_pg_aggregate) GETSTRUCT(aggTuple);

    /*
     * Figure out whether we want to use the moving-aggregate implementation,
     * and collect the right set of fields from the pg_attribute entry.
     *
     * It's possible that an aggregate would supply a safe moving-aggregate
     * implementation and an unsafe normal one, in which case our hand is
     * forced.  Otherwise, if the frame head can't move, we don't need
     * moving-aggregate code.  Even if we'd like to use it, don't do so if the
     * aggregate's arguments (and FILTER clause if any) contain any calls to
     * volatile functions.  Otherwise, the difference between restarting and
     * not restarting the aggregation would be user-visible.
     */
    if (!OidIsValid(aggform->aggminvtransfn))
        use_ma_code = false;    /* sine qua non */
    else if (aggform->aggmfinalmodify == AGGMODIFY_READ_ONLY &&
             aggform->aggfinalmodify != AGGMODIFY_READ_ONLY)
        use_ma_code = true;     /* decision forced by safety */
    else if (winstate->frameOptions & FRAMEOPTION_START_UNBOUNDED_PRECEDING)
        use_ma_code = false;    /* non-moving frame head */
    else if (contain_volatile_functions((Node *) wfunc))
        use_ma_code = false;    /* avoid possible behavioral change */
    else
        use_ma_code = true;     /* yes, let's use it */
    if (use_ma_code)
    {
        peraggstate->transfn_oid = transfn_oid = aggform->aggmtransfn;
        peraggstate->invtransfn_oid = invtransfn_oid = aggform->aggminvtransfn;
        peraggstate->finalfn_oid = finalfn_oid = aggform->aggmfinalfn;
        finalextra = aggform->aggmfinalextra;
        finalmodify = aggform->aggmfinalmodify;
        aggtranstype = aggform->aggmtranstype;
        initvalAttNo = Anum_pg_aggregate_aggminitval;
    }
    else
    {
        peraggstate->transfn_oid = transfn_oid = aggform->aggtransfn;
        peraggstate->invtransfn_oid = invtransfn_oid = InvalidOid;
        peraggstate->finalfn_oid = finalfn_oid = aggform->aggfinalfn;
        finalextra = aggform->aggfinalextra;
        finalmodify = aggform->aggfinalmodify;
        aggtranstype = aggform->aggtranstype;
        initvalAttNo = Anum_pg_aggregate_agginitval;
    }

    /*
     * ExecInitWindowAgg already checked permission to call aggregate function
     * ... but we still need to check the component functions
     */

    /* Check that aggregate owner has permission to call component fns */
    {
        HeapTuple   procTuple;
        Oid         aggOwner;

        procTuple = SearchSysCache1(PROCOID,
                                    ObjectIdGetDatum(wfunc->winfnoid));
        if (!HeapTupleIsValid(procTuple))
            elog(ERROR, "cache lookup failed for function %u",
                 wfunc->winfnoid);
        aggOwner = ((Form_pg_proc) GETSTRUCT(procTuple))->proowner;
        ReleaseSysCache(procTuple);

        aclresult = pg_proc_aclcheck(transfn_oid, aggOwner,
                                     ACL_EXECUTE);
        if (aclresult != ACLCHECK_OK)
            aclcheck_error(aclresult, OBJECT_FUNCTION,
                           get_func_name(transfn_oid));
        InvokeFunctionExecuteHook(transfn_oid);

        if (OidIsValid(invtransfn_oid))
        {
            aclresult = pg_proc_aclcheck(invtransfn_oid, aggOwner,
                                         ACL_EXECUTE);
            if (aclresult != ACLCHECK_OK)
                aclcheck_error(aclresult, OBJECT_FUNCTION,
                               get_func_name(invtransfn_oid));
            InvokeFunctionExecuteHook(invtransfn_oid);
        }

        if (OidIsValid(finalfn_oid))
        {
            aclresult = pg_proc_aclcheck(finalfn_oid, aggOwner,
                                         ACL_EXECUTE);
            if (aclresult != ACLCHECK_OK)
                aclcheck_error(aclresult, OBJECT_FUNCTION,
                               get_func_name(finalfn_oid));
            InvokeFunctionExecuteHook(finalfn_oid);
        }
    }

    /*
     * If the selected finalfn isn't read-only, we can't run this aggregate as
     * a window function.  This is a user-facing error, so we take a bit more
     * care with the error message than elsewhere in this function.
     */
    if (finalmodify != AGGMODIFY_READ_ONLY)
        ereport(ERROR,
                (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
                 errmsg("aggregate function %s does not support use as a window function",
                        format_procedure(wfunc->winfnoid))));

    /* Detect how many arguments to pass to the finalfn */
    if (finalextra)
        peraggstate->numFinalArgs = numArguments + 1;
    else
        peraggstate->numFinalArgs = 1;

    /* resolve actual type of transition state, if polymorphic */
    aggtranstype = resolve_aggregate_transtype(wfunc->winfnoid,
                                               aggtranstype,
                                               inputTypes,
                                               numArguments);

    /* build expression trees using actual argument & result types */
    build_aggregate_transfn_expr(inputTypes,
                                 numArguments,
                                 0, /* no ordered-set window functions yet */
                                 false, /* no variadic window functions yet */
                                 aggtranstype,
                                 wfunc->inputcollid,
                                 transfn_oid,
                                 invtransfn_oid,
                                 &transfnexpr,
                                 &invtransfnexpr);

    /* set up infrastructure for calling the transfn(s) and finalfn */
    fmgr_info(transfn_oid, &peraggstate->transfn);
    fmgr_info_set_expr((Node *) transfnexpr, &peraggstate->transfn);

    if (OidIsValid(invtransfn_oid))
    {
        fmgr_info(invtransfn_oid, &peraggstate->invtransfn);
        fmgr_info_set_expr((Node *) invtransfnexpr, &peraggstate->invtransfn);
    }

    if (OidIsValid(finalfn_oid))
    {
        build_aggregate_finalfn_expr(inputTypes,
                                     peraggstate->numFinalArgs,
                                     aggtranstype,
                                     wfunc->wintype,
                                     wfunc->inputcollid,
                                     finalfn_oid,
                                     &finalfnexpr);
        fmgr_info(finalfn_oid, &peraggstate->finalfn);
        fmgr_info_set_expr((Node *) finalfnexpr, &peraggstate->finalfn);
    }

    /* get info about relevant datatypes */
    get_typlenbyval(wfunc->wintype,
                    &peraggstate->resulttypeLen,
                    &peraggstate->resulttypeByVal);
    get_typlenbyval(aggtranstype,
                    &peraggstate->transtypeLen,
                    &peraggstate->transtypeByVal);

    /*
     * initval is potentially null, so don't try to access it as a struct
     * field. Must do it the hard way with SysCacheGetAttr.
     */
    textInitVal = SysCacheGetAttr(AGGFNOID, aggTuple, initvalAttNo,
                                  &peraggstate->initValueIsNull);

    if (peraggstate->initValueIsNull)
        peraggstate->initValue = (Datum) 0;
    else
        peraggstate->initValue = GetAggInitVal(textInitVal,
                                               aggtranstype);

    /*
     * If the transfn is strict and the initval is NULL, make sure input type
     * and transtype are the same (or at least binary-compatible), so that
     * it's OK to use the first input value as the initial transValue.  This
     * should have been checked at agg definition time, but we must check
     * again in case the transfn's strictness property has been changed.
     */
    if (peraggstate->transfn.fn_strict && peraggstate->initValueIsNull)
    {
        if (numArguments < 1 ||
            !IsBinaryCoercible(inputTypes[0], aggtranstype))
            ereport(ERROR,
                    (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                     errmsg("aggregate %u needs to have compatible input type and transition type",
                            wfunc->winfnoid)));
    }

    /*
     * Insist that forward and inverse transition functions have the same
     * strictness setting.  Allowing them to differ would require handling
     * more special cases in advance_windowaggregate and
     * advance_windowaggregate_base, for no discernible benefit.  This should
     * have been checked at agg definition time, but we must check again in
     * case either function's strictness property has been changed.
     */
    if (OidIsValid(invtransfn_oid) &&
        peraggstate->transfn.fn_strict != peraggstate->invtransfn.fn_strict)
        ereport(ERROR,
                (errcode(ERRCODE_INVALID_FUNCTION_DEFINITION),
                 errmsg("strictness of aggregate's forward and inverse transition functions must match")));

    /*
     * Moving aggregates use their own aggcontext.
     *
     * This is necessary because they might restart at different times, so we
     * might never be able to reset the shared context otherwise.  We can't
     * make it the aggregates' responsibility to clean up after themselves,
     * because strict aggregates must be restarted whenever we remove their
     * last non-NULL input, which the aggregate won't be aware is happening.
     * Also, just pfree()ing the transValue upon restarting wouldn't help,
     * since we'd miss any indirectly referenced data.  We could, in theory,
     * make the memory allocation rules for moving aggregates different than
     * they have historically been for plain aggregates, but that seems grotty
     * and likely to lead to memory leaks.
     */
    if (OidIsValid(invtransfn_oid))
        peraggstate->aggcontext =
            AllocSetContextCreate(CurrentMemoryContext,
                                  "WindowAgg Per Aggregate",
                                  ALLOCSET_DEFAULT_SIZES);
    else
        peraggstate->aggcontext = winstate->aggcontext;

    ReleaseSysCache(aggTuple);

    return peraggstate;
}

static Datum
GetAggInitVal(Datum textInitVal, Oid transtype)
{
    Oid         typinput,
                typioparam;
    char       *strInitVal;
    Datum       initVal;

    getTypeInputInfo(transtype, &typinput, &typioparam);
    strInitVal = TextDatumGetCString(textInitVal);
    initVal = OidInputFunctionCall(typinput, strInitVal,
                                   typioparam, -1);
    pfree(strInitVal);
    return initVal;
}

/*
 * are_peers
 * compare two rows to see if they are equal according to the ORDER BY clause
 *
 * NB: this does not consider the window frame mode.
 */
static bool
are_peers(WindowAggState *winstate, TupleTableSlot *slot1,
          TupleTableSlot *slot2)
{
    WindowAgg  *node = (WindowAgg *) winstate->ss.ps.plan;
    ExprContext *econtext = winstate->tmpcontext;

    /* If no ORDER BY, all rows are peers with each other */
    if (node->ordNumCols == 0)
        return true;

    econtext->ecxt_outertuple = slot1;
    econtext->ecxt_innertuple = slot2;
    return ExecQualAndReset(winstate->ordEqfunction, econtext);
}

/*
 * window_gettupleslot
 *  Fetch the pos'th tuple of the current partition into the slot,
 *  using the winobj's read pointer
 *
 * Returns true if successful, false if no such row
 */
static bool
window_gettupleslot(WindowObject winobj, int64 pos, TupleTableSlot *slot)
{
    WindowAggState *winstate = winobj->winstate;
    MemoryContext oldcontext;

    /* often called repeatedly in a row */
    CHECK_FOR_INTERRUPTS();

    /* Don't allow passing -1 to spool_tuples here */
    if (pos < 0)
        return false;

    /* If necessary, fetch the tuple into the spool */
    spool_tuples(winstate, pos);

    if (pos >= winstate->spooled_rows)
        return false;

    if (pos < winobj->markpos)
        elog(ERROR, "cannot fetch row before WindowObject's mark position");

    oldcontext = MemoryContextSwitchTo(winstate->ss.ps.ps_ExprContext->ecxt_per_query_memory);

    tuplestore_select_read_pointer(winstate->buffer, winobj->readptr);

    /*
     * Advance or rewind until we are within one tuple of the one we want.
     */
    if (winobj->seekpos < pos - 1)
    {
        if (!tuplestore_skiptuples(winstate->buffer,
                                   pos - 1 - winobj->seekpos,
                                   true))
            elog(ERROR, "unexpected end of tuplestore");
        winobj->seekpos = pos - 1;
    }
    else if (winobj->seekpos > pos + 1)
    {
        if (!tuplestore_skiptuples(winstate->buffer,
                                   winobj->seekpos - (pos + 1),
                                   false))
            elog(ERROR, "unexpected end of tuplestore");
        winobj->seekpos = pos + 1;
    }
    else if (winobj->seekpos == pos)
    {
        /*
         * There's no API to refetch the tuple at the current position.  We
         * have to move one tuple forward, and then one backward.  (We don't
         * do it the other way because we might try to fetch the row before
         * our mark, which isn't allowed.)  XXX this case could stand to be
         * optimized.
         */
        tuplestore_advance(winstate->buffer, true);
        winobj->seekpos++;
    }

    /*
     * Now we should be on the tuple immediately before or after the one we
     * want, so just fetch forwards or backwards as appropriate.
     */
    if (winobj->seekpos > pos)
    {
        if (!tuplestore_gettupleslot(winstate->buffer, false, true, slot))
            elog(ERROR, "unexpected end of tuplestore");
        winobj->seekpos--;
    }
    else
    {
        if (!tuplestore_gettupleslot(winstate->buffer, true, true, slot))
            elog(ERROR, "unexpected end of tuplestore");
        winobj->seekpos++;
    }

    Assert(winobj->seekpos == pos);

    MemoryContextSwitchTo(oldcontext);

    return true;
}


/***********************************************************************
 * API exposed to window functions
 ***********************************************************************/


/*
 * WinGetPartitionLocalMemory
 *      Get working memory that lives till end of partition processing
 *
 * On first call within a given partition, this allocates and zeroes the
 * requested amount of space.  Subsequent calls just return the same chunk.
 *
 * Memory obtained this way is normally used to hold state that should be
 * automatically reset for each new partition.  If a window function wants
 * to hold state across the whole query, fcinfo->fn_extra can be used in the
 * usual way for that.
 */
void *
WinGetPartitionLocalMemory(WindowObject winobj, Size sz)
{
    Assert(WindowObjectIsValid(winobj));
    if (winobj->localmem == NULL)
        winobj->localmem =
            MemoryContextAllocZero(winobj->winstate->partcontext, sz);
    return winobj->localmem;
}

/*
 * WinGetCurrentPosition
 *      Return the current row's position (counting from 0) within the current
 *      partition.
 */
int64
WinGetCurrentPosition(WindowObject winobj)
{
    Assert(WindowObjectIsValid(winobj));
    return winobj->winstate->currentpos;
}

/*
 * WinGetPartitionRowCount
 *      Return total number of rows contained in the current partition.
 *
 * Note: this is a relatively expensive operation because it forces the
 * whole partition to be "spooled" into the tuplestore at once.  Once
 * executed, however, additional calls within the same partition are cheap.
 */
int64
WinGetPartitionRowCount(WindowObject winobj)
{
    Assert(WindowObjectIsValid(winobj));
    spool_tuples(winobj->winstate, -1);
    return winobj->winstate->spooled_rows;
}

/*
 * WinSetMarkPosition
 *      Set the "mark" position for the window object, which is the oldest row
 *      number (counting from 0) it is allowed to fetch during all subsequent
 *      operations within the current partition.
 *
 * Window functions do not have to call this, but are encouraged to move the
 * mark forward when possible to keep the tuplestore size down and prevent
 * having to spill rows to disk.
 */
void
WinSetMarkPosition(WindowObject winobj, int64 markpos)
{
    WindowAggState *winstate;

    Assert(WindowObjectIsValid(winobj));
    winstate = winobj->winstate;

    if (markpos < winobj->markpos)
        elog(ERROR, "cannot move WindowObject's mark position backward");
    tuplestore_select_read_pointer(winstate->buffer, winobj->markptr);
    if (markpos > winobj->markpos)
    {
        tuplestore_skiptuples(winstate->buffer,
                              markpos - winobj->markpos,
                              true);
        winobj->markpos = markpos;
    }
    tuplestore_select_read_pointer(winstate->buffer, winobj->readptr);
    if (markpos > winobj->seekpos)
    {
        tuplestore_skiptuples(winstate->buffer,
                              markpos - winobj->seekpos,
                              true);
        winobj->seekpos = markpos;
    }
}

/*
 * WinRowsArePeers
 *      Compare two rows (specified by absolute position in partition) to see
 *      if they are equal according to the ORDER BY clause.
 *
 * NB: this does not consider the window frame mode.
 */
bool
WinRowsArePeers(WindowObject winobj, int64 pos1, int64 pos2)
{
    WindowAggState *winstate;
    WindowAgg  *node;
    TupleTableSlot *slot1;
    TupleTableSlot *slot2;
    bool        res;

    Assert(WindowObjectIsValid(winobj));
    winstate = winobj->winstate;
    node = (WindowAgg *) winstate->ss.ps.plan;

    /* If no ORDER BY, all rows are peers; don't bother to fetch them */
    if (node->ordNumCols == 0)
        return true;

    /*
     * Note: OK to use temp_slot_2 here because we aren't calling any
     * frame-related functions (those tend to clobber temp_slot_2).
     */
    slot1 = winstate->temp_slot_1;
    slot2 = winstate->temp_slot_2;

    if (!window_gettupleslot(winobj, pos1, slot1))
        elog(ERROR, "specified position is out of window: " INT64_FORMAT,
             pos1);
    if (!window_gettupleslot(winobj, pos2, slot2))
        elog(ERROR, "specified position is out of window: " INT64_FORMAT,
             pos2);

    res = are_peers(winstate, slot1, slot2);

    ExecClearTuple(slot1);
    ExecClearTuple(slot2);

    return res;
}

/*
 * WinGetFuncArgInPartition
 *      Evaluate a window function's argument expression on a specified
 *      row of the partition.  The row is identified in lseek(2) style,
 *      i.e. relative to the current, first, or last row.
 *
 * argno: argument number to evaluate (counted from 0)
 * relpos: signed rowcount offset from the seek position
 * seektype: WINDOW_SEEK_CURRENT, WINDOW_SEEK_HEAD, or WINDOW_SEEK_TAIL
 * set_mark: If the row is found and set_mark is true, the mark is moved to
 *      the row as a side-effect.
 * isnull: output argument, receives isnull status of result
 * isout: output argument, set to indicate whether target row position
 *      is out of partition (can pass NULL if caller doesn't care about this)
 *
 * Specifying a nonexistent row is not an error, it just causes a null result
 * (plus setting *isout true, if isout isn't NULL).
 */
Datum
WinGetFuncArgInPartition(WindowObject winobj, int argno,
                         int relpos, int seektype, bool set_mark,
                         bool *isnull, bool *isout)
{
    WindowAggState *winstate;
    ExprContext *econtext;
    TupleTableSlot *slot;
    bool        gottuple;
    int64       abs_pos;

    Assert(WindowObjectIsValid(winobj));
    winstate = winobj->winstate;
    econtext = winstate->ss.ps.ps_ExprContext;
    slot = winstate->temp_slot_1;

    switch (seektype)
    {
        case WINDOW_SEEK_CURRENT:
            abs_pos = winstate->currentpos + relpos;
            break;
        case WINDOW_SEEK_HEAD:
            abs_pos = relpos;
            break;
        case WINDOW_SEEK_TAIL:
            spool_tuples(winstate, -1);
            abs_pos = winstate->spooled_rows - 1 + relpos;
            break;
        default:
            elog(ERROR, "unrecognized window seek type: %d", seektype);
            abs_pos = 0;        /* keep compiler quiet */
            break;
    }

    gottuple = window_gettupleslot(winobj, abs_pos, slot);

    if (!gottuple)
    {
        if (isout)
            *isout = true;
        *isnull = true;
        return (Datum) 0;
    }
    else
    {
        if (isout)
            *isout = false;
        if (set_mark)
            WinSetMarkPosition(winobj, abs_pos);
        econtext->ecxt_outertuple = slot;
        return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
                            econtext, isnull);
    }
}

/*
 * WinGetFuncArgInFrame
 *      Evaluate a window function's argument expression on a specified
 *      row of the window frame.  The row is identified in lseek(2) style,
 *      i.e. relative to the first or last row of the frame.  (We do not
 *      support WINDOW_SEEK_CURRENT here, because it's not very clear what
 *      that should mean if the current row isn't part of the frame.)
 *
 * argno: argument number to evaluate (counted from 0)
 * relpos: signed rowcount offset from the seek position
 * seektype: WINDOW_SEEK_HEAD or WINDOW_SEEK_TAIL
 * set_mark: If the row is found/in frame and set_mark is true, the mark is
 *      moved to the row as a side-effect.
 * isnull: output argument, receives isnull status of result
 * isout: output argument, set to indicate whether target row position
 *      is out of frame (can pass NULL if caller doesn't care about this)
 *
 * Specifying a nonexistent or not-in-frame row is not an error, it just
 * causes a null result (plus setting *isout true, if isout isn't NULL).
 *
 * Note that some exclusion-clause options lead to situations where the
 * rows that are in-frame are not consecutive in the partition.  But we
 * count only in-frame rows when measuring relpos.
 *
 * The set_mark flag is interpreted as meaning that the caller will specify
 * a constant (or, perhaps, monotonically increasing) relpos in successive
 * calls, so that *if there is no exclusion clause* there will be no need
 * to fetch a row before the previously fetched row.  But we do not expect
 * the caller to know how to account for exclusion clauses.  Therefore,
 * if there is an exclusion clause we take responsibility for adjusting the
 * mark request to something that will be safe given the above assumption
 * about relpos.
 */
Datum
WinGetFuncArgInFrame(WindowObject winobj, int argno,
                     int relpos, int seektype, bool set_mark,
                     bool *isnull, bool *isout)
{
    WindowAggState *winstate;
    ExprContext *econtext;
    TupleTableSlot *slot;
    int64       abs_pos;
    int64       mark_pos;

    Assert(WindowObjectIsValid(winobj));
    winstate = winobj->winstate;
    econtext = winstate->ss.ps.ps_ExprContext;
    slot = winstate->temp_slot_1;

    switch (seektype)
    {
        case WINDOW_SEEK_CURRENT:
            elog(ERROR, "WINDOW_SEEK_CURRENT is not supported for WinGetFuncArgInFrame");
            abs_pos = mark_pos = 0; /* keep compiler quiet */
            break;
        case WINDOW_SEEK_HEAD:
            /* rejecting relpos < 0 is easy and simplifies code below */
            if (relpos < 0)
                goto out_of_frame;
            update_frameheadpos(winstate);
            abs_pos = winstate->frameheadpos + relpos;
            mark_pos = abs_pos;

            /*
             * Account for exclusion option if one is active, but advance only
             * abs_pos not mark_pos.  This prevents changes of the current
             * row's peer group from resulting in trying to fetch a row before
             * some previous mark position.
             *
             * Note that in some corner cases such as current row being
             * outside frame, these calculations are theoretically too simple,
             * but it doesn't matter because we'll end up deciding the row is
             * out of frame.  We do not attempt to avoid fetching rows past
             * end of frame; that would happen in some cases anyway.
             */
            switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
            {
                case 0:
                    /* no adjustment needed */
                    break;
                case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
                    if (abs_pos >= winstate->currentpos &&
                        winstate->currentpos >= winstate->frameheadpos)
                        abs_pos++;
                    break;
                case FRAMEOPTION_EXCLUDE_GROUP:
                    update_grouptailpos(winstate);
                    if (abs_pos >= winstate->groupheadpos &&
                        winstate->grouptailpos > winstate->frameheadpos)
                    {
                        int64       overlapstart = Max(winstate->groupheadpos,
                                                       winstate->frameheadpos);

                        abs_pos += winstate->grouptailpos - overlapstart;
                    }
                    break;
                case FRAMEOPTION_EXCLUDE_TIES:
                    update_grouptailpos(winstate);
                    if (abs_pos >= winstate->groupheadpos &&
                        winstate->grouptailpos > winstate->frameheadpos)
                    {
                        int64       overlapstart = Max(winstate->groupheadpos,
                                                       winstate->frameheadpos);

                        if (abs_pos == overlapstart)
                            abs_pos = winstate->currentpos;
                        else
                            abs_pos += winstate->grouptailpos - overlapstart - 1;
                    }
                    break;
                default:
                    elog(ERROR, "unrecognized frame option state: 0x%x",
                         winstate->frameOptions);
                    break;
            }
            break;
        case WINDOW_SEEK_TAIL:
            /* rejecting relpos > 0 is easy and simplifies code below */
            if (relpos > 0)
                goto out_of_frame;
            update_frametailpos(winstate);
            abs_pos = winstate->frametailpos - 1 + relpos;

            /*
             * Account for exclusion option if one is active.  If there is no
             * exclusion, we can safely set the mark at the accessed row.  But
             * if there is, we can only mark the frame start, because we can't
             * be sure how far back in the frame the exclusion might cause us
             * to fetch in future.  Furthermore, we have to actually check
             * against frameheadpos here, since it's unsafe to try to fetch a
             * row before frame start if the mark might be there already.
             */
            switch (winstate->frameOptions & FRAMEOPTION_EXCLUSION)
            {
                case 0:
                    /* no adjustment needed */
                    mark_pos = abs_pos;
                    break;
                case FRAMEOPTION_EXCLUDE_CURRENT_ROW:
                    if (abs_pos <= winstate->currentpos &&
                        winstate->currentpos < winstate->frametailpos)
                        abs_pos--;
                    update_frameheadpos(winstate);
                    if (abs_pos < winstate->frameheadpos)
                        goto out_of_frame;
                    mark_pos = winstate->frameheadpos;
                    break;
                case FRAMEOPTION_EXCLUDE_GROUP:
                    update_grouptailpos(winstate);
                    if (abs_pos < winstate->grouptailpos &&
                        winstate->groupheadpos < winstate->frametailpos)
                    {
                        int64       overlapend = Min(winstate->grouptailpos,
                                                     winstate->frametailpos);

                        abs_pos -= overlapend - winstate->groupheadpos;
                    }
                    update_frameheadpos(winstate);
                    if (abs_pos < winstate->frameheadpos)
                        goto out_of_frame;
                    mark_pos = winstate->frameheadpos;
                    break;
                case FRAMEOPTION_EXCLUDE_TIES:
                    update_grouptailpos(winstate);
                    if (abs_pos < winstate->grouptailpos &&
                        winstate->groupheadpos < winstate->frametailpos)
                    {
                        int64       overlapend = Min(winstate->grouptailpos,
                                                     winstate->frametailpos);

                        if (abs_pos == overlapend - 1)
                            abs_pos = winstate->currentpos;
                        else
                            abs_pos -= overlapend - 1 - winstate->groupheadpos;
                    }
                    update_frameheadpos(winstate);
                    if (abs_pos < winstate->frameheadpos)
                        goto out_of_frame;
                    mark_pos = winstate->frameheadpos;
                    break;
                default:
                    elog(ERROR, "unrecognized frame option state: 0x%x",
                         winstate->frameOptions);
                    mark_pos = 0;   /* keep compiler quiet */
                    break;
            }
            break;
        default:
            elog(ERROR, "unrecognized window seek type: %d", seektype);
            abs_pos = mark_pos = 0; /* keep compiler quiet */
            break;
    }

    if (!window_gettupleslot(winobj, abs_pos, slot))
        goto out_of_frame;

    /* The code above does not detect all out-of-frame cases, so check */
    if (row_is_in_frame(winstate, abs_pos, slot) <= 0)
        goto out_of_frame;

    if (isout)
        *isout = false;
    if (set_mark)
        WinSetMarkPosition(winobj, mark_pos);
    econtext->ecxt_outertuple = slot;
    return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
                        econtext, isnull);

out_of_frame:
    if (isout)
        *isout = true;
    *isnull = true;
    return (Datum) 0;
}

/*
 * WinGetFuncArgCurrent
 *      Evaluate a window function's argument expression on the current row.
 *
 * argno: argument number to evaluate (counted from 0)
 * isnull: output argument, receives isnull status of result
 *
 * Note: this isn't quite equivalent to WinGetFuncArgInPartition or
 * WinGetFuncArgInFrame targeting the current row, because it will succeed
 * even if the WindowObject's mark has been set beyond the current row.
 * This should generally be used for "ordinary" arguments of a window
 * function, such as the offset argument of lead() or lag().
 */
Datum
WinGetFuncArgCurrent(WindowObject winobj, int argno, bool *isnull)
{
    WindowAggState *winstate;
    ExprContext *econtext;

    Assert(WindowObjectIsValid(winobj));
    winstate = winobj->winstate;

    econtext = winstate->ss.ps.ps_ExprContext;

    econtext->ecxt_outertuple = winstate->ss.ss_ScanTupleSlot;
    return ExecEvalExpr((ExprState *) list_nth(winobj->argstates, argno),
                        econtext, isnull);
}