execTuples.c

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/*-------------------------------------------------------------------------
 *
 * execTuples.c
 *    Routines dealing with TupleTableSlots.  These are used for resource
 *    management associated with tuples (eg, releasing buffer pins for
 *    tuples in disk buffers, or freeing the memory occupied by transient
 *    tuples).  Slots also provide access abstraction that lets us implement
 *    "virtual" tuples to reduce data-copying overhead.
 *
 *    Routines dealing with the type information for tuples. Currently,
 *    the type information for a tuple is an array of FormData_pg_attribute.
 *    This information is needed by routines manipulating tuples
 *    (getattribute, formtuple, etc.).
 *
 * Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/execTuples.c
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *
 *   SLOT CREATION/DESTRUCTION
 *      MakeTupleTableSlot      - create an empty slot
 *      ExecAllocTableSlot      - create a slot within a tuple table
 *      ExecResetTupleTable     - clear and optionally delete a tuple table
 *      MakeSingleTupleTableSlot - make a standalone slot, set its descriptor
 *      ExecDropSingleTupleTableSlot - destroy a standalone slot
 *
 *   SLOT ACCESSORS
 *      ExecSetSlotDescriptor   - set a slot's tuple descriptor
 *      ExecStoreTuple          - store a physical tuple in the slot
 *      ExecStoreMinimalTuple   - store a minimal physical tuple in the slot
 *      ExecClearTuple          - clear contents of a slot
 *      ExecStoreVirtualTuple   - mark slot as containing a virtual tuple
 *      ExecCopySlotTuple       - build a physical tuple from a slot
 *      ExecCopySlotMinimalTuple - build a minimal physical tuple from a slot
 *      ExecMaterializeSlot     - convert virtual to physical storage
 *      ExecCopySlot            - copy one slot's contents to another
 *
 *   CONVENIENCE INITIALIZATION ROUTINES
 *      ExecInitResultTupleSlot    \    convenience routines to initialize
 *      ExecInitScanTupleSlot       \   the various tuple slots for nodes
 *      ExecInitExtraTupleSlot      /   which store copies of tuples.
 *      ExecInitNullTupleSlot      /
 *
 *   Routines that probably belong somewhere else:
 *      ExecTypeFromTL          - form a TupleDesc from a target list
 *
 *   EXAMPLE OF HOW TABLE ROUTINES WORK
 *      Suppose we have a query such as SELECT emp.name FROM emp and we have
 *      a single SeqScan node in the query plan.
 *
 *      At ExecutorStart()
 *      ----------------
 *      - ExecInitSeqScan() calls ExecInitScanTupleSlot() and
 *        ExecInitResultTupleSlot() to construct TupleTableSlots
 *        for the tuples returned by the access methods and the
 *        tuples resulting from performing target list projections.
 *
 *      During ExecutorRun()
 *      ----------------
 *      - SeqNext() calls ExecStoreTuple() to place the tuple returned
 *        by the access methods into the scan tuple slot.
 *
 *      - ExecSeqScan() calls ExecStoreTuple() to take the result
 *        tuple from ExecProject() and place it into the result tuple slot.
 *
 *      - ExecutePlan() calls the output function.
 *
 *      The important thing to watch in the executor code is how pointers
 *      to the slots containing tuples are passed instead of the tuples
 *      themselves.  This facilitates the communication of related information
 *      (such as whether or not a tuple should be pfreed, what buffer contains
 *      this tuple, the tuple's tuple descriptor, etc).  It also allows us
 *      to avoid physically constructing projection tuples in many cases.
 */
#include "postgres.h"

#include "access/htup_details.h"
#include "access/tuptoaster.h"
#include "funcapi.h"
#include "catalog/pg_type.h"
#include "nodes/nodeFuncs.h"
#include "storage/bufmgr.h"
#include "utils/builtins.h"
#include "utils/lsyscache.h"
#include "utils/typcache.h"


static TupleDesc ExecTypeFromTLInternal(List *targetList,
                       bool hasoid, bool skipjunk);


/* ----------------------------------------------------------------
 *                tuple table create/delete functions
 * ----------------------------------------------------------------
 */

/* --------------------------------
 *      MakeTupleTableSlot
 *
 *      Basic routine to make an empty TupleTableSlot.
 * --------------------------------
 */
TupleTableSlot *
MakeTupleTableSlot(void)
{
    TupleTableSlot *slot = makeNode(TupleTableSlot);

    slot->tts_isempty = true;
    slot->tts_shouldFree = false;
    slot->tts_shouldFreeMin = false;
    slot->tts_tuple = NULL;
    slot->tts_tupleDescriptor = NULL;
    slot->tts_mcxt = CurrentMemoryContext;
    slot->tts_buffer = InvalidBuffer;
    slot->tts_nvalid = 0;
    slot->tts_values = NULL;
    slot->tts_isnull = NULL;
    slot->tts_mintuple = NULL;

    return slot;
}

/* --------------------------------
 *      ExecAllocTableSlot
 *
 *      Create a tuple table slot within a tuple table (which is just a List).
 * --------------------------------
 */
TupleTableSlot *
ExecAllocTableSlot(List **tupleTable)
{
    TupleTableSlot *slot = MakeTupleTableSlot();

    *tupleTable = lappend(*tupleTable, slot);

    return slot;
}

/* --------------------------------
 *      ExecResetTupleTable
 *
 *      This releases any resources (buffer pins, tupdesc refcounts)
 *      held by the tuple table, and optionally releases the memory
 *      occupied by the tuple table data structure.
 *      It is expected that this routine be called by EndPlan().
 * --------------------------------
 */
void
ExecResetTupleTable(List *tupleTable,   /* tuple table */
                    bool shouldFree)    /* true if we should free memory */
{
    ListCell   *lc;

    foreach(lc, tupleTable)
    {
        TupleTableSlot *slot = lfirst_node(TupleTableSlot, lc);

        /* Always release resources and reset the slot to empty */
        ExecClearTuple(slot);
        if (slot->tts_tupleDescriptor)
        {
            ReleaseTupleDesc(slot->tts_tupleDescriptor);
            slot->tts_tupleDescriptor = NULL;
        }

        /* If shouldFree, release memory occupied by the slot itself */
        if (shouldFree)
        {
            if (slot->tts_values)
                pfree(slot->tts_values);
            if (slot->tts_isnull)
                pfree(slot->tts_isnull);
            pfree(slot);
        }
    }

    /* If shouldFree, release the list structure */
    if (shouldFree)
        list_free(tupleTable);
}

/* --------------------------------
 *      MakeSingleTupleTableSlot
 *
 *      This is a convenience routine for operations that need a
 *      standalone TupleTableSlot not gotten from the main executor
 *      tuple table.  It makes a single slot and initializes it
 *      to use the given tuple descriptor.
 * --------------------------------
 */
TupleTableSlot *
MakeSingleTupleTableSlot(TupleDesc tupdesc)
{
    TupleTableSlot *slot = MakeTupleTableSlot();

    ExecSetSlotDescriptor(slot, tupdesc);

    return slot;
}

/* --------------------------------
 *      ExecDropSingleTupleTableSlot
 *
 *      Release a TupleTableSlot made with MakeSingleTupleTableSlot.
 *      DON'T use this on a slot that's part of a tuple table list!
 * --------------------------------
 */
void
ExecDropSingleTupleTableSlot(TupleTableSlot *slot)
{
    /* This should match ExecResetTupleTable's processing of one slot */
    Assert(IsA(slot, TupleTableSlot));
    ExecClearTuple(slot);
    if (slot->tts_tupleDescriptor)
        ReleaseTupleDesc(slot->tts_tupleDescriptor);
    if (slot->tts_values)
        pfree(slot->tts_values);
    if (slot->tts_isnull)
        pfree(slot->tts_isnull);
    pfree(slot);
}


/* ----------------------------------------------------------------
 *                tuple table slot accessor functions
 * ----------------------------------------------------------------
 */

/* --------------------------------
 *      ExecSetSlotDescriptor
 *
 *      This function is used to set the tuple descriptor associated
 *      with the slot's tuple.  The passed descriptor must have lifespan
 *      at least equal to the slot's.  If it is a reference-counted descriptor
 *      then the reference count is incremented for as long as the slot holds
 *      a reference.
 * --------------------------------
 */
void
ExecSetSlotDescriptor(TupleTableSlot *slot, /* slot to change */
                      TupleDesc tupdesc)    /* new tuple descriptor */
{
    /* For safety, make sure slot is empty before changing it */
    ExecClearTuple(slot);

    /*
     * Release any old descriptor.  Also release old Datum/isnull arrays if
     * present (we don't bother to check if they could be re-used).
     */
    if (slot->tts_tupleDescriptor)
        ReleaseTupleDesc(slot->tts_tupleDescriptor);

    if (slot->tts_values)
        pfree(slot->tts_values);
    if (slot->tts_isnull)
        pfree(slot->tts_isnull);

    /*
     * Install the new descriptor; if it's refcounted, bump its refcount.
     */
    slot->tts_tupleDescriptor = tupdesc;
    PinTupleDesc(tupdesc);

    /*
     * Allocate Datum/isnull arrays of the appropriate size.  These must have
     * the same lifetime as the slot, so allocate in the slot's own context.
     */
    slot->tts_values = (Datum *)
        MemoryContextAlloc(slot->tts_mcxt, tupdesc->natts * sizeof(Datum));
    slot->tts_isnull = (bool *)
        MemoryContextAlloc(slot->tts_mcxt, tupdesc->natts * sizeof(bool));
}

/* --------------------------------
 *      ExecStoreTuple
 *
 *      This function is used to store a physical tuple into a specified
 *      slot in the tuple table.
 *
 *      tuple:  tuple to store
 *      slot:   slot to store it in
 *      buffer: disk buffer if tuple is in a disk page, else InvalidBuffer
 *      shouldFree: true if ExecClearTuple should pfree() the tuple
 *                  when done with it
 *
 * If 'buffer' is not InvalidBuffer, the tuple table code acquires a pin
 * on the buffer which is held until the slot is cleared, so that the tuple
 * won't go away on us.
 *
 * shouldFree is normally set 'true' for tuples constructed on-the-fly.
 * It must always be 'false' for tuples that are stored in disk pages,
 * since we don't want to try to pfree those.
 *
 * Another case where it is 'false' is when the referenced tuple is held
 * in a tuple table slot belonging to a lower-level executor Proc node.
 * In this case the lower-level slot retains ownership and responsibility
 * for eventually releasing the tuple.  When this method is used, we must
 * be certain that the upper-level Proc node will lose interest in the tuple
 * sooner than the lower-level one does!  If you're not certain, copy the
 * lower-level tuple with heap_copytuple and let the upper-level table
 * slot assume ownership of the copy!
 *
 * Return value is just the passed-in slot pointer.
 *
 * NOTE: before PostgreSQL 8.1, this function would accept a NULL tuple
 * pointer and effectively behave like ExecClearTuple (though you could
 * still specify a buffer to pin, which would be an odd combination).
 * This saved a couple lines of code in a few places, but seemed more likely
 * to mask logic errors than to be really useful, so it's now disallowed.
 * --------------------------------
 */
TupleTableSlot *
ExecStoreTuple(HeapTuple tuple,
               TupleTableSlot *slot,
               Buffer buffer,
               bool shouldFree)
{
    /*
     * sanity checks
     */
    Assert(tuple != NULL);
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);
    /* passing shouldFree=true for a tuple on a disk page is not sane */
    Assert(BufferIsValid(buffer) ? (!shouldFree) : true);

    /*
     * Free any old physical tuple belonging to the slot.
     */
    if (slot->tts_shouldFree)
        heap_freetuple(slot->tts_tuple);
    if (slot->tts_shouldFreeMin)
        heap_free_minimal_tuple(slot->tts_mintuple);

    /*
     * Store the new tuple into the specified slot.
     */
    slot->tts_isempty = false;
    slot->tts_shouldFree = shouldFree;
    slot->tts_shouldFreeMin = false;
    slot->tts_tuple = tuple;
    slot->tts_mintuple = NULL;

    /* Mark extracted state invalid */
    slot->tts_nvalid = 0;

    /*
     * If tuple is on a disk page, keep the page pinned as long as we hold a
     * pointer into it.  We assume the caller already has such a pin.
     *
     * This is coded to optimize the case where the slot previously held a
     * tuple on the same disk page: in that case releasing and re-acquiring
     * the pin is a waste of cycles.  This is a common situation during
     * seqscans, so it's worth troubling over.
     */
    if (slot->tts_buffer != buffer)
    {
        if (BufferIsValid(slot->tts_buffer))
            ReleaseBuffer(slot->tts_buffer);
        slot->tts_buffer = buffer;
        if (BufferIsValid(buffer))
            IncrBufferRefCount(buffer);
    }

    return slot;
}

/* --------------------------------
 *      ExecStoreMinimalTuple
 *
 *      Like ExecStoreTuple, but insert a "minimal" tuple into the slot.
 *
 * No 'buffer' parameter since minimal tuples are never stored in relations.
 * --------------------------------
 */
TupleTableSlot *
ExecStoreMinimalTuple(MinimalTuple mtup,
                      TupleTableSlot *slot,
                      bool shouldFree)
{
    /*
     * sanity checks
     */
    Assert(mtup != NULL);
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);

    /*
     * Free any old physical tuple belonging to the slot.
     */
    if (slot->tts_shouldFree)
        heap_freetuple(slot->tts_tuple);
    if (slot->tts_shouldFreeMin)
        heap_free_minimal_tuple(slot->tts_mintuple);

    /*
     * Drop the pin on the referenced buffer, if there is one.
     */
    if (BufferIsValid(slot->tts_buffer))
        ReleaseBuffer(slot->tts_buffer);

    slot->tts_buffer = InvalidBuffer;

    /*
     * Store the new tuple into the specified slot.
     */
    slot->tts_isempty = false;
    slot->tts_shouldFree = false;
    slot->tts_shouldFreeMin = shouldFree;
    slot->tts_tuple = &slot->tts_minhdr;
    slot->tts_mintuple = mtup;

    slot->tts_minhdr.t_len = mtup->t_len + MINIMAL_TUPLE_OFFSET;
    slot->tts_minhdr.t_data = (HeapTupleHeader) ((char *) mtup - MINIMAL_TUPLE_OFFSET);
    /* no need to set t_self or t_tableOid since we won't allow access */

    /* Mark extracted state invalid */
    slot->tts_nvalid = 0;

    return slot;
}

/* --------------------------------
 *      ExecClearTuple
 *
 *      This function is used to clear out a slot in the tuple table.
 *
 *      NB: only the tuple is cleared, not the tuple descriptor (if any).
 * --------------------------------
 */
TupleTableSlot *                /* return: slot passed */
ExecClearTuple(TupleTableSlot *slot)    /* slot in which to store tuple */
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);

    /*
     * Free the old physical tuple if necessary.
     */
    if (slot->tts_shouldFree)
        heap_freetuple(slot->tts_tuple);
    if (slot->tts_shouldFreeMin)
        heap_free_minimal_tuple(slot->tts_mintuple);

    slot->tts_tuple = NULL;
    slot->tts_mintuple = NULL;
    slot->tts_shouldFree = false;
    slot->tts_shouldFreeMin = false;

    /*
     * Drop the pin on the referenced buffer, if there is one.
     */
    if (BufferIsValid(slot->tts_buffer))
        ReleaseBuffer(slot->tts_buffer);

    slot->tts_buffer = InvalidBuffer;

    /*
     * Mark it empty.
     */
    slot->tts_isempty = true;
    slot->tts_nvalid = 0;

    return slot;
}

/* --------------------------------
 *      ExecStoreVirtualTuple
 *          Mark a slot as containing a virtual tuple.
 *
 * The protocol for loading a slot with virtual tuple data is:
 *      * Call ExecClearTuple to mark the slot empty.
 *      * Store data into the Datum/isnull arrays.
 *      * Call ExecStoreVirtualTuple to mark the slot valid.
 * This is a bit unclean but it avoids one round of data copying.
 * --------------------------------
 */
TupleTableSlot *
ExecStoreVirtualTuple(TupleTableSlot *slot)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);
    Assert(slot->tts_isempty);

    slot->tts_isempty = false;
    slot->tts_nvalid = slot->tts_tupleDescriptor->natts;

    return slot;
}

/* --------------------------------
 *      ExecStoreAllNullTuple
 *          Set up the slot to contain a null in every column.
 *
 * At first glance this might sound just like ExecClearTuple, but it's
 * entirely different: the slot ends up full, not empty.
 * --------------------------------
 */
TupleTableSlot *
ExecStoreAllNullTuple(TupleTableSlot *slot)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(slot->tts_tupleDescriptor != NULL);

    /* Clear any old contents */
    ExecClearTuple(slot);

    /*
     * Fill all the columns of the virtual tuple with nulls
     */
    MemSet(slot->tts_values, 0,
           slot->tts_tupleDescriptor->natts * sizeof(Datum));
    memset(slot->tts_isnull, true,
           slot->tts_tupleDescriptor->natts * sizeof(bool));

    return ExecStoreVirtualTuple(slot);
}

/* --------------------------------
 *      ExecCopySlotTuple
 *          Obtain a copy of a slot's regular physical tuple.  The copy is
 *          palloc'd in the current memory context.
 *          The slot itself is undisturbed.
 *
 *      This works even if the slot contains a virtual or minimal tuple;
 *      however the "system columns" of the result will not be meaningful.
 * --------------------------------
 */
HeapTuple
ExecCopySlotTuple(TupleTableSlot *slot)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(!slot->tts_isempty);

    /*
     * If we have a physical tuple (either format) then just copy it.
     */
    if (TTS_HAS_PHYSICAL_TUPLE(slot))
        return heap_copytuple(slot->tts_tuple);
    if (slot->tts_mintuple)
        return heap_tuple_from_minimal_tuple(slot->tts_mintuple);

    /*
     * Otherwise we need to build a tuple from the Datum array.
     */
    return heap_form_tuple(slot->tts_tupleDescriptor,
                           slot->tts_values,
                           slot->tts_isnull);
}

/* --------------------------------
 *      ExecCopySlotMinimalTuple
 *          Obtain a copy of a slot's minimal physical tuple.  The copy is
 *          palloc'd in the current memory context.
 *          The slot itself is undisturbed.
 * --------------------------------
 */
MinimalTuple
ExecCopySlotMinimalTuple(TupleTableSlot *slot)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(!slot->tts_isempty);

    /*
     * If we have a physical tuple then just copy it.  Prefer to copy
     * tts_mintuple since that's a tad cheaper.
     */
    if (slot->tts_mintuple)
        return heap_copy_minimal_tuple(slot->tts_mintuple);
    if (slot->tts_tuple)
        return minimal_tuple_from_heap_tuple(slot->tts_tuple);

    /*
     * Otherwise we need to build a tuple from the Datum array.
     */
    return heap_form_minimal_tuple(slot->tts_tupleDescriptor,
                                   slot->tts_values,
                                   slot->tts_isnull);
}

/* --------------------------------
 *      ExecFetchSlotTuple
 *          Fetch the slot's regular physical tuple.
 *
 *      If the slot contains a virtual tuple, we convert it to physical
 *      form.  The slot retains ownership of the physical tuple.
 *      If it contains a minimal tuple we convert to regular form and store
 *      that in addition to the minimal tuple (not instead of, because
 *      callers may hold pointers to Datums within the minimal tuple).
 *
 * The main difference between this and ExecMaterializeSlot() is that this
 * does not guarantee that the contained tuple is local storage.
 * Hence, the result must be treated as read-only.
 * --------------------------------
 */
HeapTuple
ExecFetchSlotTuple(TupleTableSlot *slot)
{
    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(!slot->tts_isempty);

    /*
     * If we have a regular physical tuple then just return it.
     */
    if (TTS_HAS_PHYSICAL_TUPLE(slot))
        return slot->tts_tuple;

    /*
     * Otherwise materialize the slot...
     */
    return ExecMaterializeSlot(slot);
}

/* --------------------------------
 *      ExecFetchSlotMinimalTuple
 *          Fetch the slot's minimal physical tuple.
 *
 *      If the slot contains a virtual tuple, we convert it to minimal
 *      physical form.  The slot retains ownership of the minimal tuple.
 *      If it contains a regular tuple we convert to minimal form and store
 *      that in addition to the regular tuple (not instead of, because
 *      callers may hold pointers to Datums within the regular tuple).
 *
 * As above, the result must be treated as read-only.
 * --------------------------------
 */
MinimalTuple
ExecFetchSlotMinimalTuple(TupleTableSlot *slot)
{
    MemoryContext oldContext;

    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(!slot->tts_isempty);

    /*
     * If we have a minimal physical tuple (local or not) then just return it.
     */
    if (slot->tts_mintuple)
        return slot->tts_mintuple;

    /*
     * Otherwise, copy or build a minimal tuple, and store it into the slot.
     *
     * We may be called in a context that is shorter-lived than the tuple
     * slot, but we have to ensure that the materialized tuple will survive
     * anyway.
     */
    oldContext = MemoryContextSwitchTo(slot->tts_mcxt);
    slot->tts_mintuple = ExecCopySlotMinimalTuple(slot);
    slot->tts_shouldFreeMin = true;
    MemoryContextSwitchTo(oldContext);

    /*
     * Note: we may now have a situation where we have a local minimal tuple
     * attached to a virtual or non-local physical tuple.  There seems no harm
     * in that at the moment, but if any materializes, we should change this
     * function to force the slot into minimal-tuple-only state.
     */

    return slot->tts_mintuple;
}

/* --------------------------------
 *      ExecFetchSlotTupleDatum
 *          Fetch the slot's tuple as a composite-type Datum.
 *
 *      The result is always freshly palloc'd in the caller's memory context.
 * --------------------------------
 */
Datum
ExecFetchSlotTupleDatum(TupleTableSlot *slot)
{
    HeapTuple   tup;
    TupleDesc   tupdesc;

    /* Fetch slot's contents in regular-physical-tuple form */
    tup = ExecFetchSlotTuple(slot);
    tupdesc = slot->tts_tupleDescriptor;

    /* Convert to Datum form */
    return heap_copy_tuple_as_datum(tup, tupdesc);
}

/* --------------------------------
 *      ExecMaterializeSlot
 *          Force a slot into the "materialized" state.
 *
 *      This causes the slot's tuple to be a local copy not dependent on
 *      any external storage.  A pointer to the contained tuple is returned.
 *
 *      A typical use for this operation is to prepare a computed tuple
 *      for being stored on disk.  The original data may or may not be
 *      virtual, but in any case we need a private copy for heap_insert
 *      to scribble on.
 * --------------------------------
 */
HeapTuple
ExecMaterializeSlot(TupleTableSlot *slot)
{
    MemoryContext oldContext;

    /*
     * sanity checks
     */
    Assert(slot != NULL);
    Assert(!slot->tts_isempty);

    /*
     * If we have a regular physical tuple, and it's locally palloc'd, we have
     * nothing to do.
     */
    if (slot->tts_tuple && slot->tts_shouldFree)
        return slot->tts_tuple;

    /*
     * Otherwise, copy or build a physical tuple, and store it into the slot.
     *
     * We may be called in a context that is shorter-lived than the tuple
     * slot, but we have to ensure that the materialized tuple will survive
     * anyway.
     */
    oldContext = MemoryContextSwitchTo(slot->tts_mcxt);
    slot->tts_tuple = ExecCopySlotTuple(slot);
    slot->tts_shouldFree = true;
    MemoryContextSwitchTo(oldContext);

    /*
     * Drop the pin on the referenced buffer, if there is one.
     */
    if (BufferIsValid(slot->tts_buffer))
        ReleaseBuffer(slot->tts_buffer);

    slot->tts_buffer = InvalidBuffer;

    /*
     * Mark extracted state invalid.  This is important because the slot is
     * not supposed to depend any more on the previous external data; we
     * mustn't leave any dangling pass-by-reference datums in tts_values.
     * However, we have not actually invalidated any such datums, if there
     * happen to be any previously fetched from the slot.  (Note in particular
     * that we have not pfree'd tts_mintuple, if there is one.)
     */
    slot->tts_nvalid = 0;

    /*
     * On the same principle of not depending on previous remote storage,
     * forget the mintuple if it's not local storage.  (If it is local
     * storage, we must not pfree it now, since callers might have already
     * fetched datum pointers referencing it.)
     */
    if (!slot->tts_shouldFreeMin)
        slot->tts_mintuple = NULL;

    return slot->tts_tuple;
}

/* --------------------------------
 *      ExecCopySlot
 *          Copy the source slot's contents into the destination slot.
 *
 *      The destination acquires a private copy that will not go away
 *      if the source is cleared.
 *
 *      The caller must ensure the slots have compatible tupdescs.
 * --------------------------------
 */
TupleTableSlot *
ExecCopySlot(TupleTableSlot *dstslot, TupleTableSlot *srcslot)
{
    HeapTuple   newTuple;
    MemoryContext oldContext;

    /*
     * There might be ways to optimize this when the source is virtual, but
     * for now just always build a physical copy.  Make sure it is in the
     * right context.
     */
    oldContext = MemoryContextSwitchTo(dstslot->tts_mcxt);
    newTuple = ExecCopySlotTuple(srcslot);
    MemoryContextSwitchTo(oldContext);

    return ExecStoreTuple(newTuple, dstslot, InvalidBuffer, true);
}


/* ----------------------------------------------------------------
 *              convenience initialization routines
 * ----------------------------------------------------------------
 */

/* --------------------------------
 *      ExecInit{Result,Scan,Extra}TupleSlot
 *
 *      These are convenience routines to initialize the specified slot
 *      in nodes inheriting the appropriate state.  ExecInitExtraTupleSlot
 *      is used for initializing special-purpose slots.
 * --------------------------------
 */

/* ----------------
 *      ExecInitResultTupleSlot
 * ----------------
 */
void
ExecInitResultTupleSlot(EState *estate, PlanState *planstate)
{
    planstate->ps_ResultTupleSlot = ExecAllocTableSlot(&estate->es_tupleTable);
}

/* ----------------
 *      ExecInitScanTupleSlot
 * ----------------
 */
void
ExecInitScanTupleSlot(EState *estate, ScanState *scanstate)
{
    scanstate->ss_ScanTupleSlot = ExecAllocTableSlot(&estate->es_tupleTable);
}

/* ----------------
 *      ExecInitExtraTupleSlot
 * ----------------
 */
TupleTableSlot *
ExecInitExtraTupleSlot(EState *estate)
{
    return ExecAllocTableSlot(&estate->es_tupleTable);
}

/* ----------------
 *      ExecInitNullTupleSlot
 *
 * Build a slot containing an all-nulls tuple of the given type.
 * This is used as a substitute for an input tuple when performing an
 * outer join.
 * ----------------
 */
TupleTableSlot *
ExecInitNullTupleSlot(EState *estate, TupleDesc tupType)
{
    TupleTableSlot *slot = ExecInitExtraTupleSlot(estate);

    ExecSetSlotDescriptor(slot, tupType);

    return ExecStoreAllNullTuple(slot);
}

/* ----------------------------------------------------------------
 *      ExecTypeFromTL
 *
 *      Generate a tuple descriptor for the result tuple of a targetlist.
 *      (A parse/plan tlist must be passed, not an ExprState tlist.)
 *      Note that resjunk columns, if any, are included in the result.
 *
 *      Currently there are about 4 different places where we create
 *      TupleDescriptors.  They should all be merged, or perhaps
 *      be rewritten to call BuildDesc().
 * ----------------------------------------------------------------
 */
TupleDesc
ExecTypeFromTL(List *targetList, bool hasoid)
{
    return ExecTypeFromTLInternal(targetList, hasoid, false);
}

/* ----------------------------------------------------------------
 *      ExecCleanTypeFromTL
 *
 *      Same as above, but resjunk columns are omitted from the result.
 * ----------------------------------------------------------------
 */
TupleDesc
ExecCleanTypeFromTL(List *targetList, bool hasoid)
{
    return ExecTypeFromTLInternal(targetList, hasoid, true);
}

static TupleDesc
ExecTypeFromTLInternal(List *targetList, bool hasoid, bool skipjunk)
{
    TupleDesc   typeInfo;
    ListCell   *l;
    int         len;
    int         cur_resno = 1;

    if (skipjunk)
        len = ExecCleanTargetListLength(targetList);
    else
        len = ExecTargetListLength(targetList);
    typeInfo = CreateTemplateTupleDesc(len, hasoid);

    foreach(l, targetList)
    {
        TargetEntry *tle = lfirst(l);

        if (skipjunk && tle->resjunk)
            continue;
        TupleDescInitEntry(typeInfo,
                           cur_resno,
                           tle->resname,
                           exprType((Node *) tle->expr),
                           exprTypmod((Node *) tle->expr),
                           0);
        TupleDescInitEntryCollation(typeInfo,
                                    cur_resno,
                                    exprCollation((Node *) tle->expr));
        cur_resno++;
    }

    return typeInfo;
}

/*
 * ExecTypeFromExprList - build a tuple descriptor from a list of Exprs
 *
 * This is roughly like ExecTypeFromTL, but we work from bare expressions
 * not TargetEntrys.  No names are attached to the tupledesc's columns.
 */
TupleDesc
ExecTypeFromExprList(List *exprList)
{
    TupleDesc   typeInfo;
    ListCell   *lc;
    int         cur_resno = 1;

    typeInfo = CreateTemplateTupleDesc(list_length(exprList), false);

    foreach(lc, exprList)
    {
        Node       *e = lfirst(lc);

        TupleDescInitEntry(typeInfo,
                           cur_resno,
                           NULL,
                           exprType(e),
                           exprTypmod(e),
                           0);
        TupleDescInitEntryCollation(typeInfo,
                                    cur_resno,
                                    exprCollation(e));
        cur_resno++;
    }

    return typeInfo;
}

/*
 * ExecTypeSetColNames - set column names in a TupleDesc
 *
 * Column names must be provided as an alias list (list of String nodes).
 *
 * For some callers, the supplied tupdesc has a named rowtype (not RECORD)
 * and it is moderately likely that the alias list matches the column names
 * already present in the tupdesc.  If we do change any column names then
 * we must reset the tupdesc's type to anonymous RECORD; but we avoid doing
 * so if no names change.
 */
void
ExecTypeSetColNames(TupleDesc typeInfo, List *namesList)
{
    bool        modified = false;
    int         colno = 0;
    ListCell   *lc;

    foreach(lc, namesList)
    {
        char       *cname = strVal(lfirst(lc));
        Form_pg_attribute attr;

        /* Guard against too-long names list */
        if (colno >= typeInfo->natts)
            break;
        attr = typeInfo->attrs[colno++];

        /* Ignore empty aliases (these must be for dropped columns) */
        if (cname[0] == '\0')
            continue;

        /* Change tupdesc only if alias is actually different */
        if (strcmp(cname, NameStr(attr->attname)) != 0)
        {
            namestrcpy(&(attr->attname), cname);
            modified = true;
        }
    }

    /* If we modified the tupdesc, it's now a new record type */
    if (modified)
    {
        typeInfo->tdtypeid = RECORDOID;
        typeInfo->tdtypmod = -1;
    }
}

/*
 * BlessTupleDesc - make a completed tuple descriptor useful for SRFs
 *
 * Rowtype Datums returned by a function must contain valid type information.
 * This happens "for free" if the tupdesc came from a relcache entry, but
 * not if we have manufactured a tupdesc for a transient RECORD datatype.
 * In that case we have to notify typcache.c of the existence of the type.
 */
TupleDesc
BlessTupleDesc(TupleDesc tupdesc)
{
    if (tupdesc->tdtypeid == RECORDOID &&
        tupdesc->tdtypmod < 0)
        assign_record_type_typmod(tupdesc);

    return tupdesc;             /* just for notational convenience */
}

/*
 * TupleDescGetSlot - Initialize a slot based on the supplied tupledesc
 *
 * Note: this is obsolete; it is sufficient to call BlessTupleDesc on
 * the tupdesc.  We keep it around just for backwards compatibility with
 * existing user-written SRFs.
 */
TupleTableSlot *
TupleDescGetSlot(TupleDesc tupdesc)
{
    TupleTableSlot *slot;

    /* The useful work is here */
    BlessTupleDesc(tupdesc);

    /* Make a standalone slot */
    slot = MakeSingleTupleTableSlot(tupdesc);

    /* Return the slot */
    return slot;
}

/*
 * TupleDescGetAttInMetadata - Build an AttInMetadata structure based on the
 * supplied TupleDesc. AttInMetadata can be used in conjunction with C strings
 * to produce a properly formed tuple.
 */
AttInMetadata *
TupleDescGetAttInMetadata(TupleDesc tupdesc)
{
    int         natts = tupdesc->natts;
    int         i;
    Oid         atttypeid;
    Oid         attinfuncid;
    FmgrInfo   *attinfuncinfo;
    Oid        *attioparams;
    int32      *atttypmods;
    AttInMetadata *attinmeta;

    attinmeta = (AttInMetadata *) palloc(sizeof(AttInMetadata));

    /* "Bless" the tupledesc so that we can make rowtype datums with it */
    attinmeta->tupdesc = BlessTupleDesc(tupdesc);

    /*
     * Gather info needed later to call the "in" function for each attribute
     */
    attinfuncinfo = (FmgrInfo *) palloc0(natts * sizeof(FmgrInfo));
    attioparams = (Oid *) palloc0(natts * sizeof(Oid));
    atttypmods = (int32 *) palloc0(natts * sizeof(int32));

    for (i = 0; i < natts; i++)
    {
        /* Ignore dropped attributes */
        if (!tupdesc->attrs[i]->attisdropped)
        {
            atttypeid = tupdesc->attrs[i]->atttypid;
            getTypeInputInfo(atttypeid, &attinfuncid, &attioparams[i]);
            fmgr_info(attinfuncid, &attinfuncinfo[i]);
            atttypmods[i] = tupdesc->attrs[i]->atttypmod;
        }
    }
    attinmeta->attinfuncs = attinfuncinfo;
    attinmeta->attioparams = attioparams;
    attinmeta->atttypmods = atttypmods;

    return attinmeta;
}

/*
 * BuildTupleFromCStrings - build a HeapTuple given user data in C string form.
 * values is an array of C strings, one for each attribute of the return tuple.
 * A NULL string pointer indicates we want to create a NULL field.
 */
HeapTuple
BuildTupleFromCStrings(AttInMetadata *attinmeta, char **values)
{
    TupleDesc   tupdesc = attinmeta->tupdesc;
    int         natts = tupdesc->natts;
    Datum      *dvalues;
    bool       *nulls;
    int         i;
    HeapTuple   tuple;

    dvalues = (Datum *) palloc(natts * sizeof(Datum));
    nulls = (bool *) palloc(natts * sizeof(bool));

    /* Call the "in" function for each non-dropped attribute */
    for (i = 0; i < natts; i++)
    {
        if (!tupdesc->attrs[i]->attisdropped)
        {
            /* Non-dropped attributes */
            dvalues[i] = InputFunctionCall(&attinmeta->attinfuncs[i],
                                           values[i],
                                           attinmeta->attioparams[i],
                                           attinmeta->atttypmods[i]);
            if (values[i] != NULL)
                nulls[i] = false;
            else
                nulls[i] = true;
        }
        else
        {
            /* Handle dropped attributes by setting to NULL */
            dvalues[i] = (Datum) 0;
            nulls[i] = true;
        }
    }

    /*
     * Form a tuple
     */
    tuple = heap_form_tuple(tupdesc, dvalues, nulls);

    /*
     * Release locally palloc'd space.  XXX would probably be good to pfree
     * values of pass-by-reference datums, as well.
     */
    pfree(dvalues);
    pfree(nulls);

    return tuple;
}

/*
 * HeapTupleHeaderGetDatum - convert a HeapTupleHeader pointer to a Datum.
 *
 * This must *not* get applied to an on-disk tuple; the tuple should be
 * freshly made by heap_form_tuple or some wrapper routine for it (such as
 * BuildTupleFromCStrings).  Be sure also that the tupledesc used to build
 * the tuple has a properly "blessed" rowtype.
 *
 * Formerly this was a macro equivalent to PointerGetDatum, relying on the
 * fact that heap_form_tuple fills in the appropriate tuple header fields
 * for a composite Datum.  However, we now require that composite Datums not
 * contain any external TOAST pointers.  We do not want heap_form_tuple itself
 * to enforce that; more specifically, the rule applies only to actual Datums
 * and not to HeapTuple structures.  Therefore, HeapTupleHeaderGetDatum is
 * now a function that detects whether there are externally-toasted fields
 * and constructs a new tuple with inlined fields if so.  We still need
 * heap_form_tuple to insert the Datum header fields, because otherwise this
 * code would have no way to obtain a tupledesc for the tuple.
 *
 * Note that if we do build a new tuple, it's palloc'd in the current
 * memory context.  Beware of code that changes context between the initial
 * heap_form_tuple/etc call and calling HeapTuple(Header)GetDatum.
 *
 * For performance-critical callers, it could be worthwhile to take extra
 * steps to ensure that there aren't TOAST pointers in the output of
 * heap_form_tuple to begin with.  It's likely however that the costs of the
 * typcache lookup and tuple disassembly/reassembly are swamped by TOAST
 * dereference costs, so that the benefits of such extra effort would be
 * minimal.
 *
 * XXX it would likely be better to create wrapper functions that produce
 * a composite Datum from the field values in one step.  However, there's
 * enough code using the existing APIs that we couldn't get rid of this
 * hack anytime soon.
 */
Datum
HeapTupleHeaderGetDatum(HeapTupleHeader tuple)
{
    Datum       result;
    TupleDesc   tupDesc;

    /* No work if there are no external TOAST pointers in the tuple */
    if (!HeapTupleHeaderHasExternal(tuple))
        return PointerGetDatum(tuple);

    /* Use the type data saved by heap_form_tuple to look up the rowtype */
    tupDesc = lookup_rowtype_tupdesc(HeapTupleHeaderGetTypeId(tuple),
                                     HeapTupleHeaderGetTypMod(tuple));

    /* And do the flattening */
    result = toast_flatten_tuple_to_datum(tuple,
                                          HeapTupleHeaderGetDatumLength(tuple),
                                          tupDesc);

    ReleaseTupleDesc(tupDesc);

    return result;
}


/*
 * Functions for sending tuples to the frontend (or other specified destination)
 * as though it is a SELECT result. These are used by utility commands that
 * need to project directly to the destination and don't need or want full
 * table function capability. Currently used by EXPLAIN and SHOW ALL.
 */
TupOutputState *
begin_tup_output_tupdesc(DestReceiver *dest, TupleDesc tupdesc)
{
    TupOutputState *tstate;

    tstate = (TupOutputState *) palloc(sizeof(TupOutputState));

    tstate->slot = MakeSingleTupleTableSlot(tupdesc);
    tstate->dest = dest;

    (*tstate->dest->rStartup) (tstate->dest, (int) CMD_SELECT, tupdesc);

    return tstate;
}

/*
 * write a single tuple
 */
void
do_tup_output(TupOutputState *tstate, Datum *values, bool *isnull)
{
    TupleTableSlot *slot = tstate->slot;
    int         natts = slot->tts_tupleDescriptor->natts;

    /* make sure the slot is clear */
    ExecClearTuple(slot);

    /* insert data */
    memcpy(slot->tts_values, values, natts * sizeof(Datum));
    memcpy(slot->tts_isnull, isnull, natts * sizeof(bool));

    /* mark slot as containing a virtual tuple */
    ExecStoreVirtualTuple(slot);

    /* send the tuple to the receiver */
    (void) (*tstate->dest->receiveSlot) (slot, tstate->dest);

    /* clean up */
    ExecClearTuple(slot);
}

/*
 * write a chunk of text, breaking at newline characters
 *
 * Should only be used with a single-TEXT-attribute tupdesc.
 */
void
do_text_output_multiline(TupOutputState *tstate, const char *txt)
{
    Datum       values[1];
    bool        isnull[1] = {false};

    while (*txt)
    {
        const char *eol;
        int         len;

        eol = strchr(txt, '\n');
        if (eol)
        {
            len = eol - txt;
            eol++;
        }
        else
        {
            len = strlen(txt);
            eol = txt + len;
        }

        values[0] = PointerGetDatum(cstring_to_text_with_len(txt, len));
        do_tup_output(tstate, values, isnull);
        pfree(DatumGetPointer(values[0]));
        txt = eol;
    }
}

void
end_tup_output(TupOutputState *tstate)
{
    (*tstate->dest->rShutdown) (tstate->dest);
    /* note that destroying the dest is not ours to do */
    ExecDropSingleTupleTableSlot(tstate->slot);
    pfree(tstate);
}