nodeWorktablescan.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * nodeWorktablescan.c
 *    routines to handle WorkTableScan nodes.
 *
 * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeWorktablescan.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "executor/executor.h"
#include "executor/nodeWorktablescan.h"
 
static TupleTableSlot *WorkTableScanNext(WorkTableScanState *node);
 
/* ----------------------------------------------------------------
 *      WorkTableScanNext
 *
 *      This is a workhorse for ExecWorkTableScan
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
WorkTableScanNext(WorkTableScanState *node)
{
    TupleTableSlot *slot;
    Tuplestorestate *tuplestorestate;
 
    /*
     * get information from the estate and scan state
     *
     * Note: we intentionally do not support backward scan.  Although it would
     * take only a couple more lines here, it would force nodeRecursiveunion.c
     * to create the tuplestore with backward scan enabled, which has a
     * performance cost.  In practice backward scan is never useful for a
     * worktable plan node, since it cannot appear high enough in the plan
     * tree of a scrollable cursor to be exposed to a backward-scan
     * requirement.  So it's not worth expending effort to support it.
     *
     * Note: we are also assuming that this node is the only reader of the
     * worktable.  Therefore, we don't need a private read pointer for the
     * tuplestore, nor do we need to tell tuplestore_gettupleslot to copy.
     */
    Assert(ScanDirectionIsForward(node->ss.ps.state->es_direction));
 
    tuplestorestate = node->rustate->working_table;
 
    /*
     * Get the next tuple from tuplestore. Return NULL if no more tuples.
     */
    slot = node->ss.ss_ScanTupleSlot;
    (void) tuplestore_gettupleslot(tuplestorestate, true, false, slot);
    return slot;
}
 
/*
 * WorkTableScanRecheck -- access method routine to recheck a tuple in EvalPlanQual
 */
static bool
WorkTableScanRecheck(WorkTableScanState *node, TupleTableSlot *slot)
{
    /* nothing to check */
    return true;
}
 
/* ----------------------------------------------------------------
 *      ExecWorkTableScan(node)
 *
 *      Scans the worktable sequentially and returns the next qualifying tuple.
 *      We call the ExecScan() routine and pass it the appropriate
 *      access method functions.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecWorkTableScan(PlanState *pstate)
{
    WorkTableScanState *node = castNode(WorkTableScanState, pstate);
 
    /*
     * On the first call, find the ancestor RecursiveUnion's state via the
     * Param slot reserved for it.  (We can't do this during node init because
     * there are corner cases where we'll get the init call before the
     * RecursiveUnion does.)
     */
    if (node->rustate == NULL)
    {
        WorkTableScan *plan = (WorkTableScan *) node->ss.ps.plan;
        EState     *estate = node->ss.ps.state;
        ParamExecData *param;
 
        param = &(estate->es_param_exec_vals[plan->wtParam]);
        Assert(param->execPlan == NULL);
        Assert(!param->isnull);
        node->rustate = castNode(RecursiveUnionState, DatumGetPointer(param->value));
        Assert(node->rustate);
 
        /*
         * The scan tuple type (ie, the rowtype we expect to find in the work
         * table) is the same as the result rowtype of the ancestor
         * RecursiveUnion node.  Note this depends on the assumption that
         * RecursiveUnion doesn't allow projection.
         */
        ExecAssignScanType(&node->ss,
                           ExecGetResultType(&node->rustate->ps));
 
        /*
         * Now we can initialize the projection info.  This must be completed
         * before we can call ExecScan().
         */
        ExecAssignScanProjectionInfo(&node->ss);
    }
 
    return ExecScan(&node->ss,
                    (ExecScanAccessMtd) WorkTableScanNext,
                    (ExecScanRecheckMtd) WorkTableScanRecheck);
}
 
 
/* ----------------------------------------------------------------
 *      ExecInitWorkTableScan
 * ----------------------------------------------------------------
 */
WorkTableScanState *
ExecInitWorkTableScan(WorkTableScan *node, EState *estate, int eflags)
{
    WorkTableScanState *scanstate;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    /*
     * WorkTableScan should not have any children.
     */
    Assert(outerPlan(node) == NULL);
    Assert(innerPlan(node) == NULL);
 
    /*
     * create new WorkTableScanState for node
     */
    scanstate = makeNode(WorkTableScanState);
    scanstate->ss.ps.plan = (Plan *) node;
    scanstate->ss.ps.state = estate;
    scanstate->ss.ps.ExecProcNode = ExecWorkTableScan;
    scanstate->rustate = NULL;  /* we'll set this later */
 
    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &scanstate->ss.ps);
 
    /*
     * tuple table initialization
     */
    ExecInitResultTypeTL(&scanstate->ss.ps);
 
    /* signal that return type is not yet known */
    scanstate->ss.ps.resultopsset = true;
    scanstate->ss.ps.resultopsfixed = false;
 
    ExecInitScanTupleSlot(estate, &scanstate->ss, NULL, &TTSOpsMinimalTuple);
 
    /*
     * initialize child expressions
     */
    scanstate->ss.ps.qual =
        ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
 
    /*
     * Do not yet initialize projection info, see ExecWorkTableScan() for
     * details.
     */
 
    return scanstate;
}
 
/* ----------------------------------------------------------------
 *      ExecReScanWorkTableScan
 *
 *      Rescans the relation.
 * ----------------------------------------------------------------
 */
void
ExecReScanWorkTableScan(WorkTableScanState *node)
{
    if (node->ss.ps.ps_ResultTupleSlot)
        ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
 
    ExecScanReScan(&node->ss);
 
    /* No need (or way) to rescan if ExecWorkTableScan not called yet */
    if (node->rustate)
        tuplestore_rescan(node->rustate->working_table);
}