nodeNamedtuplestorescan.c

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/*-------------------------------------------------------------------------
 *
 * nodeNamedtuplestorescan.c
 *    routines to handle NamedTuplestoreScan nodes.
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeNamedtuplestorescan.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "executor/executor.h"
#include "executor/nodeNamedtuplestorescan.h"
#include "utils/queryenvironment.h"
 
static TupleTableSlot *NamedTuplestoreScanNext(NamedTuplestoreScanState *node);
 
/* ----------------------------------------------------------------
 *      NamedTuplestoreScanNext
 *
 *      This is a workhorse for ExecNamedTuplestoreScan
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
NamedTuplestoreScanNext(NamedTuplestoreScanState *node)
{
    TupleTableSlot *slot;
 
    /* We intentionally do not support backward scan. */
    Assert(ScanDirectionIsForward(node->ss.ps.state->es_direction));
 
    /*
     * Get the next tuple from tuplestore. Return NULL if no more tuples.
     */
    slot = node->ss.ss_ScanTupleSlot;
    tuplestore_select_read_pointer(node->relation, node->readptr);
    (void) tuplestore_gettupleslot(node->relation, true, false, slot);
    return slot;
}
 
/*
 * NamedTuplestoreScanRecheck -- access method routine to recheck a tuple in
 * EvalPlanQual
 */
static bool
NamedTuplestoreScanRecheck(NamedTuplestoreScanState *node, TupleTableSlot *slot)
{
    /* nothing to check */
    return true;
}
 
/* ----------------------------------------------------------------
 *      ExecNamedTuplestoreScan(node)
 *
 *      Scans the CTE sequentially and returns the next qualifying tuple.
 *      We call the ExecScan() routine and pass it the appropriate
 *      access method functions.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecNamedTuplestoreScan(PlanState *pstate)
{
    NamedTuplestoreScanState *node = castNode(NamedTuplestoreScanState, pstate);
 
    return ExecScan(&node->ss,
                    (ExecScanAccessMtd) NamedTuplestoreScanNext,
                    (ExecScanRecheckMtd) NamedTuplestoreScanRecheck);
}
 
 
/* ----------------------------------------------------------------
 *      ExecInitNamedTuplestoreScan
 * ----------------------------------------------------------------
 */
NamedTuplestoreScanState *
ExecInitNamedTuplestoreScan(NamedTuplestoreScan *node, EState *estate, int eflags)
{
    NamedTuplestoreScanState *scanstate;
    EphemeralNamedRelation enr;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    /*
     * NamedTuplestoreScan should not have any children.
     */
    Assert(outerPlan(node) == NULL);
    Assert(innerPlan(node) == NULL);
 
    /*
     * create new NamedTuplestoreScanState for node
     */
    scanstate = makeNode(NamedTuplestoreScanState);
    scanstate->ss.ps.plan = (Plan *) node;
    scanstate->ss.ps.state = estate;
    scanstate->ss.ps.ExecProcNode = ExecNamedTuplestoreScan;
 
    enr = get_ENR(estate->es_queryEnv, node->enrname);
    if (!enr)
        elog(ERROR, "executor could not find named tuplestore \"%s\"",
             node->enrname);
 
    Assert(enr->reldata);
    scanstate->relation = (Tuplestorestate *) enr->reldata;
    scanstate->tupdesc = ENRMetadataGetTupDesc(&(enr->md));
    scanstate->readptr =
        tuplestore_alloc_read_pointer(scanstate->relation, EXEC_FLAG_REWIND);
 
    /*
     * The new read pointer copies its position from read pointer 0, which
     * could be anywhere, so explicitly rewind it.
     */
    tuplestore_select_read_pointer(scanstate->relation, scanstate->readptr);
    tuplestore_rescan(scanstate->relation);
 
    /*
     * XXX: Should we add a function to free that read pointer when done?
     *
     * This was attempted, but it did not improve performance or memory usage
     * in any tested cases.
     */
 
    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &scanstate->ss.ps);
 
    /*
     * The scan tuple type is specified for the tuplestore.
     */
    ExecInitScanTupleSlot(estate, &scanstate->ss, scanstate->tupdesc,
                          &TTSOpsMinimalTuple);
 
    /*
     * Initialize result type and projection.
     */
    ExecInitResultTypeTL(&scanstate->ss.ps);
    ExecAssignScanProjectionInfo(&scanstate->ss);
 
    /*
     * initialize child expressions
     */
    scanstate->ss.ps.qual =
        ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
 
    return scanstate;
}
 
/* ----------------------------------------------------------------
 *      ExecReScanNamedTuplestoreScan
 *
 *      Rescans the relation.
 * ----------------------------------------------------------------
 */
void
ExecReScanNamedTuplestoreScan(NamedTuplestoreScanState *node)
{
    Tuplestorestate *tuplestorestate = node->relation;
 
    if (node->ss.ps.ps_ResultTupleSlot)
        ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
 
    ExecScanReScan(&node->ss);
 
    /*
     * Rewind my own pointer.
     */
    tuplestore_select_read_pointer(tuplestorestate, node->readptr);
    tuplestore_rescan(tuplestorestate);
}