nodeRecursiveunion.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * nodeRecursiveunion.c
 *    routines to handle RecursiveUnion nodes.
 *
 * To implement UNION (without ALL), we need a hashtable that stores tuples
 * already seen.  The hash key is computed from the grouping columns.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeRecursiveunion.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"
 
#include "executor/executor.h"
#include "executor/nodeRecursiveunion.h"
#include "miscadmin.h"
#include "utils/memutils.h"
#include "utils/tuplestore.h"
 
 
 
/*
 * Initialize the hash table to empty.
 */
static void
build_hash_table(RecursiveUnionState *rustate)
{
    RecursiveUnion *node = (RecursiveUnion *) rustate->ps.plan;
    TupleDesc   desc = ExecGetResultType(outerPlanState(rustate));
 
    Assert(node->numCols > 0);
 
    /*
     * If both child plans deliver the same fixed tuple slot type, we can tell
     * BuildTupleHashTable to expect that slot type as input.  Otherwise,
     * we'll pass NULL denoting that any slot type is possible.
     */
    rustate->hashtable = BuildTupleHashTable(&rustate->ps,
                                             desc,
                                             ExecGetCommonChildSlotOps(&rustate->ps),
                                             node->numCols,
                                             node->dupColIdx,
                                             rustate->eqfuncoids,
                                             rustate->hashfunctions,
                                             node->dupCollations,
                                             node->numGroups,
                                             0,
                                             rustate->ps.state->es_query_cxt,
                                             rustate->tuplesContext,
                                             rustate->tempContext,
                                             false);
}
 
 
/* ----------------------------------------------------------------
 *      ExecRecursiveUnion(node)
 *
 *      Scans the recursive query sequentially and returns the next
 *      qualifying tuple.
 *
 * 1. evaluate non recursive term and assign the result to RT
 *
 * 2. execute recursive terms
 *
 * 2.1 WT := RT
 * 2.2 while WT is not empty repeat 2.3 to 2.6. if WT is empty returns RT
 * 2.3 replace the name of recursive term with WT
 * 2.4 evaluate the recursive term and store into WT
 * 2.5 append WT to RT
 * 2.6 go back to 2.2
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecRecursiveUnion(PlanState *pstate)
{
    RecursiveUnionState *node = castNode(RecursiveUnionState, pstate);
    PlanState  *outerPlan = outerPlanState(node);
    PlanState  *innerPlan = innerPlanState(node);
    RecursiveUnion *plan = (RecursiveUnion *) node->ps.plan;
    TupleTableSlot *slot;
    bool        isnew;
 
    CHECK_FOR_INTERRUPTS();
 
    /* 1. Evaluate non-recursive term */
    if (!node->recursing)
    {
        for (;;)
        {
            slot = ExecProcNode(outerPlan);
            if (TupIsNull(slot))
                break;
            if (plan->numCols > 0)
            {
                /* Find or build hashtable entry for this tuple's group */
                LookupTupleHashEntry(node->hashtable, slot, &isnew, NULL);
                /* Must reset temp context after each hashtable lookup */
                MemoryContextReset(node->tempContext);
                /* Ignore tuple if already seen */
                if (!isnew)
                    continue;
            }
            /* Each non-duplicate tuple goes to the working table ... */
            tuplestore_puttupleslot(node->working_table, slot);
            /* ... and to the caller */
            return slot;
        }
        node->recursing = true;
    }
 
    /* 2. Execute recursive term */
    for (;;)
    {
        slot = ExecProcNode(innerPlan);
        if (TupIsNull(slot))
        {
            Tuplestorestate *swaptemp;
 
            /* Done if there's nothing in the intermediate table */
            if (node->intermediate_empty)
                break;
 
            /*
             * Now we let the intermediate table become the work table.  We
             * need a fresh intermediate table, so delete the tuples from the
             * current working table and use that as the new intermediate
             * table.  This saves a round of free/malloc from creating a new
             * tuple store.
             */
            tuplestore_clear(node->working_table);
 
            swaptemp = node->working_table;
            node->working_table = node->intermediate_table;
            node->intermediate_table = swaptemp;
 
            /* mark the intermediate table as empty */
            node->intermediate_empty = true;
 
            /* reset the recursive term */
            innerPlan->chgParam = bms_add_member(innerPlan->chgParam,
                                                 plan->wtParam);
 
            /* and continue fetching from recursive term */
            continue;
        }
 
        if (plan->numCols > 0)
        {
            /* Find or build hashtable entry for this tuple's group */
            LookupTupleHashEntry(node->hashtable, slot, &isnew, NULL);
            /* Must reset temp context after each hashtable lookup */
            MemoryContextReset(node->tempContext);
            /* Ignore tuple if already seen */
            if (!isnew)
                continue;
        }
 
        /* Else, tuple is good; stash it in intermediate table ... */
        node->intermediate_empty = false;
        tuplestore_puttupleslot(node->intermediate_table, slot);
        /* ... and return it */
        return slot;
    }
 
    return NULL;
}
 
/* ----------------------------------------------------------------
 *      ExecInitRecursiveUnion
 * ----------------------------------------------------------------
 */
RecursiveUnionState *
ExecInitRecursiveUnion(RecursiveUnion *node, EState *estate, int eflags)
{
    RecursiveUnionState *rustate;
    ParamExecData *prmdata;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    /*
     * create state structure
     */
    rustate = makeNode(RecursiveUnionState);
    rustate->ps.plan = (Plan *) node;
    rustate->ps.state = estate;
    rustate->ps.ExecProcNode = ExecRecursiveUnion;
 
    rustate->eqfuncoids = NULL;
    rustate->hashfunctions = NULL;
    rustate->hashtable = NULL;
    rustate->tempContext = NULL;
    rustate->tuplesContext = NULL;
 
    /* initialize processing state */
    rustate->recursing = false;
    rustate->intermediate_empty = true;
    rustate->working_table = tuplestore_begin_heap(false, false, work_mem);
    rustate->intermediate_table = tuplestore_begin_heap(false, false, work_mem);
 
    /*
     * If hashing, we need a per-tuple memory context for comparisons, and a
     * longer-lived context to store the hash table.  The table can't just be
     * kept in the per-query context because we want to be able to throw it
     * away when rescanning.  We can use a BumpContext to save storage,
     * because we will have no need to delete individual table entries.
     */
    if (node->numCols > 0)
    {
        rustate->tempContext =
            AllocSetContextCreate(CurrentMemoryContext,
                                  "RecursiveUnion",
                                  ALLOCSET_DEFAULT_SIZES);
        rustate->tuplesContext =
            BumpContextCreate(CurrentMemoryContext,
                              "RecursiveUnion hashed tuples",
                              ALLOCSET_DEFAULT_SIZES);
    }
 
    /*
     * Make the state structure available to descendant WorkTableScan nodes
     * via the Param slot reserved for it.
     */
    prmdata = &(estate->es_param_exec_vals[node->wtParam]);
    Assert(prmdata->execPlan == NULL);
    prmdata->value = PointerGetDatum(rustate);
    prmdata->isnull = false;
 
    /*
     * Miscellaneous initialization
     *
     * RecursiveUnion plans don't have expression contexts because they never
     * call ExecQual or ExecProject.
     */
    Assert(node->plan.qual == NIL);
 
    /*
     * RecursiveUnion nodes still have Result slots, which hold pointers to
     * tuples, so we have to initialize them.
     */
    ExecInitResultTypeTL(&rustate->ps);
 
    /*
     * Initialize result tuple type.  (Note: we have to set up the result type
     * before initializing child nodes, because nodeWorktablescan.c expects it
     * to be valid.)
     */
    rustate->ps.ps_ProjInfo = NULL;
 
    /*
     * initialize child nodes
     */
    outerPlanState(rustate) = ExecInitNode(outerPlan(node), estate, eflags);
    innerPlanState(rustate) = ExecInitNode(innerPlan(node), estate, eflags);
 
    /*
     * If hashing, precompute fmgr lookup data for inner loop, and create the
     * hash table.
     */
    if (node->numCols > 0)
    {
        execTuplesHashPrepare(node->numCols,
                              node->dupOperators,
                              &rustate->eqfuncoids,
                              &rustate->hashfunctions);
        build_hash_table(rustate);
    }
 
    return rustate;
}
 
/* ----------------------------------------------------------------
 *      ExecEndRecursiveUnion
 *
 *      frees any storage allocated through C routines.
 * ----------------------------------------------------------------
 */
void
ExecEndRecursiveUnion(RecursiveUnionState *node)
{
    /* Release tuplestores */
    tuplestore_end(node->working_table);
    tuplestore_end(node->intermediate_table);
 
    /* free subsidiary stuff including hashtable data */
    if (node->tempContext)
        MemoryContextDelete(node->tempContext);
    if (node->tuplesContext)
        MemoryContextDelete(node->tuplesContext);
 
    /*
     * close down subplans
     */
    ExecEndNode(outerPlanState(node));
    ExecEndNode(innerPlanState(node));
}
 
/* ----------------------------------------------------------------
 *      ExecReScanRecursiveUnion
 *
 *      Rescans the relation.
 * ----------------------------------------------------------------
 */
void
ExecReScanRecursiveUnion(RecursiveUnionState *node)
{
    PlanState  *outerPlan = outerPlanState(node);
    PlanState  *innerPlan = innerPlanState(node);
    RecursiveUnion *plan = (RecursiveUnion *) node->ps.plan;
 
    /*
     * Set recursive term's chgParam to tell it that we'll modify the working
     * table and therefore it has to rescan.
     */
    innerPlan->chgParam = bms_add_member(innerPlan->chgParam, plan->wtParam);
 
    /*
     * if chgParam of subnode is not null then plan will be re-scanned by
     * first ExecProcNode.  Because of above, we only have to do this to the
     * non-recursive term.
     */
    if (outerPlan->chgParam == NULL)
        ExecReScan(outerPlan);
 
    /* Empty hashtable if needed */
    if (plan->numCols > 0)
        ResetTupleHashTable(node->hashtable);
 
    /* reset processing state */
    node->recursing = false;
    node->intermediate_empty = true;
    tuplestore_clear(node->working_table);
    tuplestore_clear(node->intermediate_table);
}