nodeProjectSet.c

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/*-------------------------------------------------------------------------
 *
 * nodeProjectSet.c
 *    support for evaluating targetlists containing set-returning functions
 *
 * DESCRIPTION
 *
 *      ProjectSet nodes are inserted by the planner to evaluate set-returning
 *      functions in the targetlist.  It's guaranteed that all set-returning
 *      functions are directly at the top level of the targetlist, i.e. they
 *      can't be inside more-complex expressions.  If that'd otherwise be
 *      the case, the planner adds additional ProjectSet nodes.
 *
 * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeProjectSet.c
 *
 *-------------------------------------------------------------------------
 */

#include "postgres.h"

#include "executor/executor.h"
#include "executor/nodeProjectSet.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "utils/memutils.h"


static TupleTableSlot *ExecProjectSRF(ProjectSetState *node, bool continuing);


/* ----------------------------------------------------------------
 *      ExecProjectSet(node)
 *
 *      Return tuples after evaluating the targetlist (which contains set
 *      returning functions).
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecProjectSet(PlanState *pstate)
{
    ProjectSetState *node = castNode(ProjectSetState, pstate);
    TupleTableSlot *outerTupleSlot;
    TupleTableSlot *resultSlot;
    PlanState  *outerPlan;
    ExprContext *econtext;

    CHECK_FOR_INTERRUPTS();

    econtext = node->ps.ps_ExprContext;

    /*
     * Reset per-tuple context to free expression-evaluation storage allocated
     * for a potentially previously returned tuple. Note that the SRF argument
     * context has a different lifetime and is reset below.
     */
    ResetExprContext(econtext);

    /*
     * Check to see if we're still projecting out tuples from a previous scan
     * tuple (because there is a function-returning-set in the projection
     * expressions).  If so, try to project another one.
     */
    if (node->pending_srf_tuples)
    {
        resultSlot = ExecProjectSRF(node, true);

        if (resultSlot != NULL)
            return resultSlot;
    }

    /*
     * Reset argument context to free any expression evaluation storage
     * allocated in the previous tuple cycle.  Note this can't happen until
     * we're done projecting out tuples from a scan tuple, as ValuePerCall
     * functions are allowed to reference the arguments for each returned
     * tuple.
     */
    MemoryContextReset(node->argcontext);

    /*
     * Get another input tuple and project SRFs from it.
     */
    for (;;)
    {
        /*
         * Retrieve tuples from the outer plan until there are no more.
         */
        outerPlan = outerPlanState(node);
        outerTupleSlot = ExecProcNode(outerPlan);

        if (TupIsNull(outerTupleSlot))
            return NULL;

        /*
         * Prepare to compute projection expressions, which will expect to
         * access the input tuples as varno OUTER.
         */
        econtext->ecxt_outertuple = outerTupleSlot;

        /* Evaluate the expressions */
        resultSlot = ExecProjectSRF(node, false);

        /*
         * Return the tuple unless the projection produced no rows (due to an
         * empty set), in which case we must loop back to see if there are
         * more outerPlan tuples.
         */
        if (resultSlot)
            return resultSlot;
    }

    return NULL;
}

/* ----------------------------------------------------------------
 *      ExecProjectSRF
 *
 *      Project a targetlist containing one or more set-returning functions.
 *
 *      'continuing' indicates whether to continue projecting rows for the
 *      same input tuple; or whether a new input tuple is being projected.
 *
 *      Returns NULL if no output tuple has been produced.
 *
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecProjectSRF(ProjectSetState *node, bool continuing)
{
    TupleTableSlot *resultSlot = node->ps.ps_ResultTupleSlot;
    ExprContext *econtext = node->ps.ps_ExprContext;
    MemoryContext oldcontext;
    bool        hassrf PG_USED_FOR_ASSERTS_ONLY;
    bool        hasresult;
    int         argno;

    ExecClearTuple(resultSlot);

    /* Call SRFs, as well as plain expressions, in per-tuple context */
    oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);

    /*
     * Assume no further tuples are produced unless an ExprMultipleResult is
     * encountered from a set returning function.
     */
    node->pending_srf_tuples = false;

    hassrf = hasresult = false;
    for (argno = 0; argno < node->nelems; argno++)
    {
        Node       *elem = node->elems[argno];
        ExprDoneCond *isdone = &node->elemdone[argno];
        Datum      *result = &resultSlot->tts_values[argno];
        bool       *isnull = &resultSlot->tts_isnull[argno];

        if (continuing && *isdone == ExprEndResult)
        {
            /*
             * If we're continuing to project output rows from a source tuple,
             * return NULLs once the SRF has been exhausted.
             */
            *result = (Datum) 0;
            *isnull = true;
            hassrf = true;
        }
        else if (IsA(elem, SetExprState))
        {
            /*
             * Evaluate SRF - possibly continuing previously started output.
             */
            *result = ExecMakeFunctionResultSet((SetExprState *) elem,
                                                econtext, node->argcontext,
                                                isnull, isdone);

            if (*isdone != ExprEndResult)
                hasresult = true;
            if (*isdone == ExprMultipleResult)
                node->pending_srf_tuples = true;
            hassrf = true;
        }
        else
        {
            /* Non-SRF tlist expression, just evaluate normally. */
            *result = ExecEvalExpr((ExprState *) elem, econtext, isnull);
            *isdone = ExprSingleResult;
        }
    }

    MemoryContextSwitchTo(oldcontext);

    /* ProjectSet should not be used if there's no SRFs */
    Assert(hassrf);

    /*
     * If all the SRFs returned ExprEndResult, we consider that as no row
     * being produced.
     */
    if (hasresult)
    {
        ExecStoreVirtualTuple(resultSlot);
        return resultSlot;
    }

    return NULL;
}

/* ----------------------------------------------------------------
 *      ExecInitProjectSet
 *
 *      Creates the run-time state information for the ProjectSet node
 *      produced by the planner and initializes outer relations
 *      (child nodes).
 * ----------------------------------------------------------------
 */
ProjectSetState *
ExecInitProjectSet(ProjectSet *node, EState *estate, int eflags)
{
    ProjectSetState *state;
    ListCell   *lc;
    int         off;

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

    /*
     * create state structure
     */
    state = makeNode(ProjectSetState);
    state->ps.plan = (Plan *) node;
    state->ps.state = estate;
    state->ps.ExecProcNode = ExecProjectSet;

    state->pending_srf_tuples = false;

    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &state->ps);

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

    /*
     * we don't use inner plan
     */
    Assert(innerPlan(node) == NULL);

    /*
     * tuple table and result type initialization
     */
    ExecInitResultTupleSlotTL(&state->ps, &TTSOpsVirtual);

    /* Create workspace for per-tlist-entry expr state & SRF-is-done state */
    state->nelems = list_length(node->plan.targetlist);
    state->elems = (Node **)
        palloc(sizeof(Node *) * state->nelems);
    state->elemdone = (ExprDoneCond *)
        palloc(sizeof(ExprDoneCond) * state->nelems);

    /*
     * Build expressions to evaluate targetlist.  We can't use
     * ExecBuildProjectionInfo here, since that doesn't deal with SRFs.
     * Instead compile each expression separately, using
     * ExecInitFunctionResultSet where applicable.
     */
    off = 0;
    foreach(lc, node->plan.targetlist)
    {
        TargetEntry *te = (TargetEntry *) lfirst(lc);
        Expr       *expr = te->expr;

        if ((IsA(expr, FuncExpr) && ((FuncExpr *) expr)->funcretset) ||
            (IsA(expr, OpExpr) && ((OpExpr *) expr)->opretset))
        {
            state->elems[off] = (Node *)
                ExecInitFunctionResultSet(expr, state->ps.ps_ExprContext,
                                          &state->ps);
        }
        else
        {
            Assert(!expression_returns_set((Node *) expr));
            state->elems[off] = (Node *) ExecInitExpr(expr, &state->ps);
        }

        off++;
    }

    /* We don't support any qual on ProjectSet nodes */
    Assert(node->plan.qual == NIL);

    /*
     * Create a memory context that ExecMakeFunctionResultSet can use to
     * evaluate function arguments in.  We can't use the per-tuple context for
     * this because it gets reset too often; but we don't want to leak
     * evaluation results into the query-lifespan context either.  We use one
     * context for the arguments of all tSRFs, as they have roughly equivalent
     * lifetimes.
     */
    state->argcontext = AllocSetContextCreate(CurrentMemoryContext,
                                              "tSRF function arguments",
                                              ALLOCSET_DEFAULT_SIZES);

    return state;
}

/* ----------------------------------------------------------------
 *      ExecEndProjectSet
 *
 *      frees up storage allocated through C routines
 * ----------------------------------------------------------------
 */
void
ExecEndProjectSet(ProjectSetState *node)
{
    /*
     * Free the exprcontext
     */
    ExecFreeExprContext(&node->ps);

    /*
     * clean out the tuple table
     */
    ExecClearTuple(node->ps.ps_ResultTupleSlot);

    /*
     * shut down subplans
     */
    ExecEndNode(outerPlanState(node));
}

void
ExecReScanProjectSet(ProjectSetState *node)
{
    /* Forget any incompletely-evaluated SRFs */
    node->pending_srf_tuples = false;

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