nodeMergeAppend.c

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/*-------------------------------------------------------------------------
 *
 * nodeMergeAppend.c
 *    routines to handle MergeAppend nodes.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeMergeAppend.c
 *
 *-------------------------------------------------------------------------
 */
/* INTERFACE ROUTINES
 *      ExecInitMergeAppend     - initialize the MergeAppend node
 *      ExecMergeAppend         - retrieve the next tuple from the node
 *      ExecEndMergeAppend      - shut down the MergeAppend node
 *      ExecReScanMergeAppend   - rescan the MergeAppend node
 *
 *   NOTES
 *      A MergeAppend node contains a list of one or more subplans.
 *      These are each expected to deliver tuples that are sorted according
 *      to a common sort key.  The MergeAppend node merges these streams
 *      to produce output sorted the same way.
 *
 *      MergeAppend nodes don't make use of their left and right
 *      subtrees, rather they maintain a list of subplans so
 *      a typical MergeAppend node looks like this in the plan tree:
 *
 *                 ...
 *                 /
 *              MergeAppend---+------+------+--- nil
 *              /   \         |      |      |
 *            nil   nil      ...    ...    ...
 *                               subplans
 */
 
#include "postgres.h"
 
#include "executor/executor.h"
#include "executor/execPartition.h"
#include "executor/nodeMergeAppend.h"
#include "lib/binaryheap.h"
#include "miscadmin.h"
#include "utils/sortsupport.h"
 
/*
 * We have one slot for each item in the heap array.  We use SlotNumber
 * to store slot indexes.  This doesn't actually provide any formal
 * type-safety, but it makes the code more self-documenting.
 */
typedef int32 SlotNumber;
 
static TupleTableSlot *ExecMergeAppend(PlanState *pstate);
static int  heap_compare_slots(Datum a, Datum b, void *arg);
 
 
/* ----------------------------------------------------------------
 *      ExecInitMergeAppend
 *
 *      Begin all of the subscans of the MergeAppend node.
 * ----------------------------------------------------------------
 */
MergeAppendState *
ExecInitMergeAppend(MergeAppend *node, EState *estate, int eflags)
{
    MergeAppendState *mergestate = makeNode(MergeAppendState);
    PlanState **mergeplanstates;
    const TupleTableSlotOps *mergeops;
    Bitmapset  *validsubplans;
    int         nplans;
    int         i,
                j;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    /*
     * create new MergeAppendState for our node
     */
    mergestate->ps.plan = (Plan *) node;
    mergestate->ps.state = estate;
    mergestate->ps.ExecProcNode = ExecMergeAppend;
 
    /* If run-time partition pruning is enabled, then set that up now */
    if (node->part_prune_index >= 0)
    {
        PartitionPruneState *prunestate;
 
        /*
         * Set up pruning data structure.  This also initializes the set of
         * subplans to initialize (validsubplans) by taking into account the
         * result of performing initial pruning if any.
         */
        prunestate = ExecInitPartitionExecPruning(&mergestate->ps,
                                                  list_length(node->mergeplans),
                                                  node->part_prune_index,
                                                  node->apprelids,
                                                  &validsubplans);
        mergestate->ms_prune_state = prunestate;
        nplans = bms_num_members(validsubplans);
 
        /*
         * When no run-time pruning is required and there's at least one
         * subplan, we can fill ms_valid_subplans immediately, preventing
         * later calls to ExecFindMatchingSubPlans.
         */
        if (!prunestate->do_exec_prune && nplans > 0)
            mergestate->ms_valid_subplans = bms_add_range(NULL, 0, nplans - 1);
    }
    else
    {
        nplans = list_length(node->mergeplans);
 
        /*
         * When run-time partition pruning is not enabled we can just mark all
         * subplans as valid; they must also all be initialized.
         */
        Assert(nplans > 0);
        mergestate->ms_valid_subplans = validsubplans =
            bms_add_range(NULL, 0, nplans - 1);
        mergestate->ms_prune_state = NULL;
    }
 
    mergeplanstates = palloc_array(PlanState *, nplans);
    mergestate->mergeplans = mergeplanstates;
    mergestate->ms_nplans = nplans;
 
    mergestate->ms_slots = palloc0_array(TupleTableSlot *, nplans);
    mergestate->ms_heap = binaryheap_allocate(nplans, heap_compare_slots,
                                              mergestate);
 
    /*
     * call ExecInitNode on each of the valid plans to be executed and save
     * the results into the mergeplanstates array.
     */
    j = 0;
    i = -1;
    while ((i = bms_next_member(validsubplans, i)) >= 0)
    {
        Plan       *initNode = (Plan *) list_nth(node->mergeplans, i);
 
        mergeplanstates[j++] = ExecInitNode(initNode, estate, eflags);
    }
 
    /*
     * Initialize MergeAppend's result tuple type and slot.  If the child
     * plans all produce the same fixed slot type, we can use that slot type;
     * otherwise make a virtual slot.  (Note that the result slot itself is
     * used only to return a null tuple at end of execution; real tuples are
     * returned to the caller in the children's own result slots.  What we are
     * doing here is allowing the parent plan node to optimize if the
     * MergeAppend will return only one kind of slot.)
     */
    mergeops = ExecGetCommonSlotOps(mergeplanstates, j);
    if (mergeops != NULL)
    {
        ExecInitResultTupleSlotTL(&mergestate->ps, mergeops);
    }
    else
    {
        ExecInitResultTupleSlotTL(&mergestate->ps, &TTSOpsVirtual);
        /* show that the output slot type is not fixed */
        mergestate->ps.resultopsset = true;
        mergestate->ps.resultopsfixed = false;
    }
 
    /*
     * Miscellaneous initialization
     */
    mergestate->ps.ps_ProjInfo = NULL;
 
    /*
     * initialize sort-key information
     */
    mergestate->ms_nkeys = node->numCols;
    mergestate->ms_sortkeys = palloc0_array(SortSupportData, node->numCols);
 
    for (i = 0; i < node->numCols; i++)
    {
        SortSupport sortKey = mergestate->ms_sortkeys + i;
 
        sortKey->ssup_cxt = CurrentMemoryContext;
        sortKey->ssup_collation = node->collations[i];
        sortKey->ssup_nulls_first = node->nullsFirst[i];
        sortKey->ssup_attno = node->sortColIdx[i];
 
        /*
         * It isn't feasible to perform abbreviated key conversion, since
         * tuples are pulled into mergestate's binary heap as needed.  It
         * would likely be counter-productive to convert tuples into an
         * abbreviated representation as they're pulled up, so opt out of that
         * additional optimization entirely.
         */
        sortKey->abbreviate = false;
 
        PrepareSortSupportFromOrderingOp(node->sortOperators[i], sortKey);
    }
 
    /*
     * initialize to show we have not run the subplans yet
     */
    mergestate->ms_initialized = false;
 
    return mergestate;
}
 
/* ----------------------------------------------------------------
 *     ExecMergeAppend
 *
 *      Handles iteration over multiple subplans.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecMergeAppend(PlanState *pstate)
{
    MergeAppendState *node = castNode(MergeAppendState, pstate);
    TupleTableSlot *result;
    SlotNumber  i;
 
    CHECK_FOR_INTERRUPTS();
 
    if (!node->ms_initialized)
    {
        /* Nothing to do if all subplans were pruned */
        if (node->ms_nplans == 0)
            return ExecClearTuple(node->ps.ps_ResultTupleSlot);
 
        /*
         * If we've yet to determine the valid subplans then do so now.  If
         * run-time pruning is disabled then the valid subplans will always be
         * set to all subplans.
         */
        if (node->ms_valid_subplans == NULL)
            node->ms_valid_subplans =
                ExecFindMatchingSubPlans(node->ms_prune_state, false, NULL);
 
        /*
         * First time through: pull the first tuple from each valid subplan,
         * and set up the heap.
         */
        i = -1;
        while ((i = bms_next_member(node->ms_valid_subplans, i)) >= 0)
        {
            node->ms_slots[i] = ExecProcNode(node->mergeplans[i]);
            if (!TupIsNull(node->ms_slots[i]))
                binaryheap_add_unordered(node->ms_heap, Int32GetDatum(i));
        }
        binaryheap_build(node->ms_heap);
        node->ms_initialized = true;
    }
    else
    {
        /*
         * Otherwise, pull the next tuple from whichever subplan we returned
         * from last time, and reinsert the subplan index into the heap,
         * because it might now compare differently against the existing
         * elements of the heap.  (We could perhaps simplify the logic a bit
         * by doing this before returning from the prior call, but it's better
         * to not pull tuples until necessary.)
         */
        i = DatumGetInt32(binaryheap_first(node->ms_heap));
        node->ms_slots[i] = ExecProcNode(node->mergeplans[i]);
        if (!TupIsNull(node->ms_slots[i]))
            binaryheap_replace_first(node->ms_heap, Int32GetDatum(i));
        else
            (void) binaryheap_remove_first(node->ms_heap);
    }
 
    if (binaryheap_empty(node->ms_heap))
    {
        /* All the subplans are exhausted, and so is the heap */
        result = ExecClearTuple(node->ps.ps_ResultTupleSlot);
    }
    else
    {
        i = DatumGetInt32(binaryheap_first(node->ms_heap));
        result = node->ms_slots[i];
    }
 
    return result;
}
 
/*
 * Compare the tuples in the two given slots.
 */
static int32
heap_compare_slots(Datum a, Datum b, void *arg)
{
    MergeAppendState *node = (MergeAppendState *) arg;
    SlotNumber  slot1 = DatumGetInt32(a);
    SlotNumber  slot2 = DatumGetInt32(b);
 
    TupleTableSlot *s1 = node->ms_slots[slot1];
    TupleTableSlot *s2 = node->ms_slots[slot2];
    int         nkey;
 
    Assert(!TupIsNull(s1));
    Assert(!TupIsNull(s2));
 
    for (nkey = 0; nkey < node->ms_nkeys; nkey++)
    {
        SortSupport sortKey = node->ms_sortkeys + nkey;
        AttrNumber  attno = sortKey->ssup_attno;
        Datum       datum1,
                    datum2;
        bool        isNull1,
                    isNull2;
        int         compare;
 
        datum1 = slot_getattr(s1, attno, &isNull1);
        datum2 = slot_getattr(s2, attno, &isNull2);
 
        compare = ApplySortComparator(datum1, isNull1,
                                      datum2, isNull2,
                                      sortKey);
        if (compare != 0)
        {
            INVERT_COMPARE_RESULT(compare);
            return compare;
        }
    }
    return 0;
}
 
/* ----------------------------------------------------------------
 *      ExecEndMergeAppend
 *
 *      Shuts down the subscans of the MergeAppend node.
 *
 *      Returns nothing of interest.
 * ----------------------------------------------------------------
 */
void
ExecEndMergeAppend(MergeAppendState *node)
{
    PlanState **mergeplans;
    int         nplans;
    int         i;
 
    /*
     * get information from the node
     */
    mergeplans = node->mergeplans;
    nplans = node->ms_nplans;
 
    /*
     * shut down each of the subscans
     */
    for (i = 0; i < nplans; i++)
        ExecEndNode(mergeplans[i]);
}
 
void
ExecReScanMergeAppend(MergeAppendState *node)
{
    int         i;
 
    /*
     * If any PARAM_EXEC Params used in pruning expressions have changed, then
     * we'd better unset the valid subplans so that they are reselected for
     * the new parameter values.
     */
    if (node->ms_prune_state &&
        bms_overlap(node->ps.chgParam,
                    node->ms_prune_state->execparamids))
    {
        bms_free(node->ms_valid_subplans);
        node->ms_valid_subplans = NULL;
    }
 
    for (i = 0; i < node->ms_nplans; i++)
    {
        PlanState  *subnode = node->mergeplans[i];
 
        /*
         * ExecReScan doesn't know about my subplans, so I have to do
         * changed-parameter signaling myself.
         */
        if (node->ps.chgParam != NULL)
            UpdateChangedParamSet(subnode, node->ps.chgParam);
 
        /*
         * If chgParam of subnode is not null then plan will be re-scanned by
         * first ExecProcNode.
         */
        if (subnode->chgParam == NULL)
            ExecReScan(subnode);
    }
    binaryheap_reset(node->ms_heap);
    node->ms_initialized = false;
}