nodeNestloop.c

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/*-------------------------------------------------------------------------
 *
 * nodeNestloop.c
 *    routines to support nest-loop joins
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeNestloop.c
 *
 *-------------------------------------------------------------------------
 */
/*
 *   INTERFACE ROUTINES
 *      ExecNestLoop     - process a nestloop join of two plans
 *      ExecInitNestLoop - initialize the join
 *      ExecEndNestLoop  - shut down the join
 */
 
#include "postgres.h"
 
#include "executor/execdebug.h"
#include "executor/nodeNestloop.h"
#include "miscadmin.h"
 
 
/* ----------------------------------------------------------------
 *      ExecNestLoop(node)
 *
 * old comments
 *      Returns the tuple joined from inner and outer tuples which
 *      satisfies the qualification clause.
 *
 *      It scans the inner relation to join with current outer tuple.
 *
 *      If none is found, next tuple from the outer relation is retrieved
 *      and the inner relation is scanned from the beginning again to join
 *      with the outer tuple.
 *
 *      NULL is returned if all the remaining outer tuples are tried and
 *      all fail to join with the inner tuples.
 *
 *      NULL is also returned if there is no tuple from inner relation.
 *
 *      Conditions:
 *        -- outerTuple contains current tuple from outer relation and
 *           the right son(inner relation) maintains "cursor" at the tuple
 *           returned previously.
 *              This is achieved by maintaining a scan position on the outer
 *              relation.
 *
 *      Initial States:
 *        -- the outer child and the inner child
 *             are prepared to return the first tuple.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecNestLoop(PlanState *pstate)
{
    NestLoopState *node = castNode(NestLoopState, pstate);
    NestLoop   *nl;
    PlanState  *innerPlan;
    PlanState  *outerPlan;
    TupleTableSlot *outerTupleSlot;
    TupleTableSlot *innerTupleSlot;
    ExprState  *joinqual;
    ExprState  *otherqual;
    ExprContext *econtext;
    ListCell   *lc;
 
    CHECK_FOR_INTERRUPTS();
 
    /*
     * get information from the node
     */
    ENL1_printf("getting info from node");
 
    nl = (NestLoop *) node->js.ps.plan;
    joinqual = node->js.joinqual;
    otherqual = node->js.ps.qual;
    outerPlan = outerPlanState(node);
    innerPlan = innerPlanState(node);
    econtext = node->js.ps.ps_ExprContext;
 
    /*
     * Reset per-tuple memory context to free any expression evaluation
     * storage allocated in the previous tuple cycle.
     */
    ResetExprContext(econtext);
 
    /*
     * Ok, everything is setup for the join so now loop until we return a
     * qualifying join tuple.
     */
    ENL1_printf("entering main loop");
 
    for (;;)
    {
        /*
         * If we don't have an outer tuple, get the next one and reset the
         * inner scan.
         */
        if (node->nl_NeedNewOuter)
        {
            ENL1_printf("getting new outer tuple");
            outerTupleSlot = ExecProcNode(outerPlan);
 
            /*
             * if there are no more outer tuples, then the join is complete..
             */
            if (TupIsNull(outerTupleSlot))
            {
                ENL1_printf("no outer tuple, ending join");
                return NULL;
            }
 
            ENL1_printf("saving new outer tuple information");
            econtext->ecxt_outertuple = outerTupleSlot;
            node->nl_NeedNewOuter = false;
            node->nl_MatchedOuter = false;
 
            /*
             * fetch the values of any outer Vars that must be passed to the
             * inner scan, and store them in the appropriate PARAM_EXEC slots.
             */
            foreach(lc, nl->nestParams)
            {
                NestLoopParam *nlp = (NestLoopParam *) lfirst(lc);
                int         paramno = nlp->paramno;
                ParamExecData *prm;
 
                prm = &(econtext->ecxt_param_exec_vals[paramno]);
                /* Param value should be an OUTER_VAR var */
                Assert(IsA(nlp->paramval, Var));
                Assert(nlp->paramval->varno == OUTER_VAR);
                Assert(nlp->paramval->varattno > 0);
                prm->value = slot_getattr(outerTupleSlot,
                                          nlp->paramval->varattno,
                                          &(prm->isnull));
                /* Flag parameter value as changed */
                innerPlan->chgParam = bms_add_member(innerPlan->chgParam,
                                                     paramno);
            }
 
            /*
             * now rescan the inner plan
             */
            ENL1_printf("rescanning inner plan");
            ExecReScan(innerPlan);
        }
 
        /*
         * we have an outerTuple, try to get the next inner tuple.
         */
        ENL1_printf("getting new inner tuple");
 
        innerTupleSlot = ExecProcNode(innerPlan);
        econtext->ecxt_innertuple = innerTupleSlot;
 
        if (TupIsNull(innerTupleSlot))
        {
            ENL1_printf("no inner tuple, need new outer tuple");
 
            node->nl_NeedNewOuter = true;
 
            if (!node->nl_MatchedOuter &&
                (node->js.jointype == JOIN_LEFT ||
                 node->js.jointype == JOIN_ANTI))
            {
                /*
                 * We are doing an outer join and there were no join matches
                 * for this outer tuple.  Generate a fake join tuple with
                 * nulls for the inner tuple, and return it if it passes the
                 * non-join quals.
                 */
                econtext->ecxt_innertuple = node->nl_NullInnerTupleSlot;
 
                ENL1_printf("testing qualification for outer-join tuple");
 
                if (otherqual == NULL || ExecQual(otherqual, econtext))
                {
                    /*
                     * qualification was satisfied so we project and return
                     * the slot containing the result tuple using
                     * ExecProject().
                     */
                    ENL1_printf("qualification succeeded, projecting tuple");
 
                    return ExecProject(node->js.ps.ps_ProjInfo);
                }
                else
                    InstrCountFiltered2(node, 1);
            }
 
            /*
             * Otherwise just return to top of loop for a new outer tuple.
             */
            continue;
        }
 
        /*
         * at this point we have a new pair of inner and outer tuples so we
         * test the inner and outer tuples to see if they satisfy the node's
         * qualification.
         *
         * Only the joinquals determine MatchedOuter status, but all quals
         * must pass to actually return the tuple.
         */
        ENL1_printf("testing qualification");
 
        if (ExecQual(joinqual, econtext))
        {
            node->nl_MatchedOuter = true;
 
            /* In an antijoin, we never return a matched tuple */
            if (node->js.jointype == JOIN_ANTI)
            {
                node->nl_NeedNewOuter = true;
                continue;       /* return to top of loop */
            }
 
            /*
             * If we only need to join to the first matching inner tuple, then
             * consider returning this one, but after that continue with next
             * outer tuple.
             */
            if (node->js.single_match)
                node->nl_NeedNewOuter = true;
 
            if (otherqual == NULL || ExecQual(otherqual, econtext))
            {
                /*
                 * qualification was satisfied so we project and return the
                 * slot containing the result tuple using ExecProject().
                 */
                ENL1_printf("qualification succeeded, projecting tuple");
 
                return ExecProject(node->js.ps.ps_ProjInfo);
            }
            else
                InstrCountFiltered2(node, 1);
        }
        else
            InstrCountFiltered1(node, 1);
 
        /*
         * Tuple fails qual, so free per-tuple memory and try again.
         */
        ResetExprContext(econtext);
 
        ENL1_printf("qualification failed, looping");
    }
}
 
/* ----------------------------------------------------------------
 *      ExecInitNestLoop
 * ----------------------------------------------------------------
 */
NestLoopState *
ExecInitNestLoop(NestLoop *node, EState *estate, int eflags)
{
    NestLoopState *nlstate;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    NL1_printf("ExecInitNestLoop: %s\n",
               "initializing node");
 
    /*
     * create state structure
     */
    nlstate = makeNode(NestLoopState);
    nlstate->js.ps.plan = (Plan *) node;
    nlstate->js.ps.state = estate;
    nlstate->js.ps.ExecProcNode = ExecNestLoop;
 
    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &nlstate->js.ps);
 
    /*
     * initialize child nodes
     *
     * If we have no parameters to pass into the inner rel from the outer,
     * tell the inner child that cheap rescans would be good.  If we do have
     * such parameters, then there is no point in REWIND support at all in the
     * inner child, because it will always be rescanned with fresh parameter
     * values.
     */
    outerPlanState(nlstate) = ExecInitNode(outerPlan(node), estate, eflags);
    if (node->nestParams == NIL)
        eflags |= EXEC_FLAG_REWIND;
    else
        eflags &= ~EXEC_FLAG_REWIND;
    innerPlanState(nlstate) = ExecInitNode(innerPlan(node), estate, eflags);
 
    /*
     * Initialize result slot, type and projection.
     */
    ExecInitResultTupleSlotTL(&nlstate->js.ps, &TTSOpsVirtual);
    ExecAssignProjectionInfo(&nlstate->js.ps, NULL);
 
    /*
     * initialize child expressions
     */
    nlstate->js.ps.qual =
        ExecInitQual(node->join.plan.qual, (PlanState *) nlstate);
    nlstate->js.jointype = node->join.jointype;
    nlstate->js.joinqual =
        ExecInitQual(node->join.joinqual, (PlanState *) nlstate);
 
    /*
     * detect whether we need only consider the first matching inner tuple
     */
    nlstate->js.single_match = (node->join.inner_unique ||
                                node->join.jointype == JOIN_SEMI);
 
    /* set up null tuples for outer joins, if needed */
    switch (node->join.jointype)
    {
        case JOIN_INNER:
        case JOIN_SEMI:
            break;
        case JOIN_LEFT:
        case JOIN_ANTI:
            nlstate->nl_NullInnerTupleSlot =
                ExecInitNullTupleSlot(estate,
                                      ExecGetResultType(innerPlanState(nlstate)),
                                      &TTSOpsVirtual);
            break;
        default:
            elog(ERROR, "unrecognized join type: %d",
                 (int) node->join.jointype);
    }
 
    /*
     * finally, wipe the current outer tuple clean.
     */
    nlstate->nl_NeedNewOuter = true;
    nlstate->nl_MatchedOuter = false;
 
    NL1_printf("ExecInitNestLoop: %s\n",
               "node initialized");
 
    return nlstate;
}
 
/* ----------------------------------------------------------------
 *      ExecEndNestLoop
 *
 *      closes down scans and frees allocated storage
 * ----------------------------------------------------------------
 */
void
ExecEndNestLoop(NestLoopState *node)
{
    NL1_printf("ExecEndNestLoop: %s\n",
               "ending node processing");
 
    /*
     * close down subplans
     */
    ExecEndNode(outerPlanState(node));
    ExecEndNode(innerPlanState(node));
 
    NL1_printf("ExecEndNestLoop: %s\n",
               "node processing ended");
}
 
/* ----------------------------------------------------------------
 *      ExecReScanNestLoop
 * ----------------------------------------------------------------
 */
void
ExecReScanNestLoop(NestLoopState *node)
{
    PlanState  *outerPlan = outerPlanState(node);
 
    /*
     * If outerPlan->chgParam is not null then plan will be automatically
     * re-scanned by first ExecProcNode.
     */
    if (outerPlan->chgParam == NULL)
        ExecReScan(outerPlan);
 
    /*
     * innerPlan is re-scanned for each new outer tuple and MUST NOT be
     * re-scanned from here or you'll get troubles from inner index scans when
     * outer Vars are used as run-time keys...
     */
 
    node->nl_NeedNewOuter = true;
    node->nl_MatchedOuter = false;
}