nodeForeignscan.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * nodeForeignscan.c
 *    Routines to support scans of foreign tables
 *
 * Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeForeignscan.c
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *
 *      ExecForeignScan         scans a foreign table.
 *      ExecInitForeignScan     creates and initializes state info.
 *      ExecReScanForeignScan   rescans the foreign relation.
 *      ExecEndForeignScan      releases any resources allocated.
 */
#include "postgres.h"
 
#include "executor/executor.h"
#include "executor/nodeForeignscan.h"
#include "foreign/fdwapi.h"
#include "utils/rel.h"
 
static TupleTableSlot *ForeignNext(ForeignScanState *node);
static bool ForeignRecheck(ForeignScanState *node, TupleTableSlot *slot);
 
 
/* ----------------------------------------------------------------
 *      ForeignNext
 *
 *      This is a workhorse for ExecForeignScan
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ForeignNext(ForeignScanState *node)
{
    TupleTableSlot *slot;
    ForeignScan *plan = (ForeignScan *) node->ss.ps.plan;
    ExprContext *econtext = node->ss.ps.ps_ExprContext;
    MemoryContext oldcontext;
 
    /* Call the Iterate function in short-lived context */
    oldcontext = MemoryContextSwitchTo(econtext->ecxt_per_tuple_memory);
    if (plan->operation != CMD_SELECT)
    {
        /*
         * direct modifications cannot be re-evaluated, so shouldn't get here
         * during EvalPlanQual processing
         */
        Assert(node->ss.ps.state->es_epq_active == NULL);
 
        slot = node->fdwroutine->IterateDirectModify(node);
    }
    else
        slot = node->fdwroutine->IterateForeignScan(node);
    MemoryContextSwitchTo(oldcontext);
 
    /*
     * Insert valid value into tableoid, the only actually-useful system
     * column.
     */
    if (plan->fsSystemCol && !TupIsNull(slot))
        slot->tts_tableOid = RelationGetRelid(node->ss.ss_currentRelation);
 
    return slot;
}
 
/*
 * ForeignRecheck -- access method routine to recheck a tuple in EvalPlanQual
 */
static bool
ForeignRecheck(ForeignScanState *node, TupleTableSlot *slot)
{
    FdwRoutine *fdwroutine = node->fdwroutine;
    ExprContext *econtext;
 
    /*
     * extract necessary information from foreign scan node
     */
    econtext = node->ss.ps.ps_ExprContext;
 
    /* Does the tuple meet the remote qual condition? */
    econtext->ecxt_scantuple = slot;
 
    ResetExprContext(econtext);
 
    /*
     * If an outer join is pushed down, RecheckForeignScan may need to store a
     * different tuple in the slot, because a different set of columns may go
     * to NULL upon recheck.  Otherwise, it shouldn't need to change the slot
     * contents, just return true or false to indicate whether the quals still
     * pass.  For simple cases, setting fdw_recheck_quals may be easier than
     * providing this callback.
     */
    if (fdwroutine->RecheckForeignScan &&
        !fdwroutine->RecheckForeignScan(node, slot))
        return false;
 
    return ExecQual(node->fdw_recheck_quals, econtext);
}
 
/* ----------------------------------------------------------------
 *      ExecForeignScan(node)
 *
 *      Fetches the next tuple from the FDW, checks local quals, and
 *      returns it.
 *      We call the ExecScan() routine and pass it the appropriate
 *      access method functions.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecForeignScan(PlanState *pstate)
{
    ForeignScanState *node = castNode(ForeignScanState, pstate);
    ForeignScan *plan = (ForeignScan *) node->ss.ps.plan;
    EState     *estate = node->ss.ps.state;
 
    /*
     * Ignore direct modifications when EvalPlanQual is active --- they are
     * irrelevant for EvalPlanQual rechecking
     */
    if (estate->es_epq_active != NULL && plan->operation != CMD_SELECT)
        return NULL;
 
    return ExecScan(&node->ss,
                    (ExecScanAccessMtd) ForeignNext,
                    (ExecScanRecheckMtd) ForeignRecheck);
}
 
 
/* ----------------------------------------------------------------
 *      ExecInitForeignScan
 * ----------------------------------------------------------------
 */
ForeignScanState *
ExecInitForeignScan(ForeignScan *node, EState *estate, int eflags)
{
    ForeignScanState *scanstate;
    Relation    currentRelation = NULL;
    Index       scanrelid = node->scan.scanrelid;
    int         tlistvarno;
    FdwRoutine *fdwroutine;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    /*
     * create state structure
     */
    scanstate = makeNode(ForeignScanState);
    scanstate->ss.ps.plan = (Plan *) node;
    scanstate->ss.ps.state = estate;
    scanstate->ss.ps.ExecProcNode = ExecForeignScan;
 
    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &scanstate->ss.ps);
 
    /*
     * open the scan relation, if any; also acquire function pointers from the
     * FDW's handler
     */
    if (scanrelid > 0)
    {
        currentRelation = ExecOpenScanRelation(estate, scanrelid, eflags);
        scanstate->ss.ss_currentRelation = currentRelation;
        fdwroutine = GetFdwRoutineForRelation(currentRelation, true);
    }
    else
    {
        /* We can't use the relcache, so get fdwroutine the hard way */
        fdwroutine = GetFdwRoutineByServerId(node->fs_server);
    }
 
    /*
     * Determine the scan tuple type.  If the FDW provided a targetlist
     * describing the scan tuples, use that; else use base relation's rowtype.
     */
    if (node->fdw_scan_tlist != NIL || currentRelation == NULL)
    {
        TupleDesc   scan_tupdesc;
 
        scan_tupdesc = ExecTypeFromTL(node->fdw_scan_tlist);
        ExecInitScanTupleSlot(estate, &scanstate->ss, scan_tupdesc,
                              &TTSOpsHeapTuple);
        /* Node's targetlist will contain Vars with varno = INDEX_VAR */
        tlistvarno = INDEX_VAR;
    }
    else
    {
        TupleDesc   scan_tupdesc;
 
        /* don't trust FDWs to return tuples fulfilling NOT NULL constraints */
        scan_tupdesc = CreateTupleDescCopy(RelationGetDescr(currentRelation));
        ExecInitScanTupleSlot(estate, &scanstate->ss, scan_tupdesc,
                              &TTSOpsHeapTuple);
        /* Node's targetlist will contain Vars with varno = scanrelid */
        tlistvarno = scanrelid;
    }
 
    /* Don't know what an FDW might return */
    scanstate->ss.ps.scanopsfixed = false;
    scanstate->ss.ps.scanopsset = true;
 
    /*
     * Initialize result slot, type and projection.
     */
    ExecInitResultTypeTL(&scanstate->ss.ps);
    ExecAssignScanProjectionInfoWithVarno(&scanstate->ss, tlistvarno);
 
    /*
     * initialize child expressions
     */
    scanstate->ss.ps.qual =
        ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
    scanstate->fdw_recheck_quals =
        ExecInitQual(node->fdw_recheck_quals, (PlanState *) scanstate);
 
    /*
     * Determine whether to scan the foreign relation asynchronously or not;
     * this has to be kept in sync with the code in ExecInitAppend().
     */
    scanstate->ss.ps.async_capable = (((Plan *) node)->async_capable &&
                                      estate->es_epq_active == NULL);
 
    /*
     * Initialize FDW-related state.
     */
    scanstate->fdwroutine = fdwroutine;
    scanstate->fdw_state = NULL;
 
    /*
     * For the FDW's convenience, look up the modification target relation's
     * ResultRelInfo.  The ModifyTable node should have initialized it for us,
     * see ExecInitModifyTable.
     *
     * Don't try to look up the ResultRelInfo when EvalPlanQual is active,
     * though.  Direct modifications cannot be re-evaluated as part of
     * EvalPlanQual.  The lookup wouldn't work anyway because during
     * EvalPlanQual processing, EvalPlanQual only initializes the subtree
     * under the ModifyTable, and doesn't run ExecInitModifyTable.
     */
    if (node->resultRelation > 0 && estate->es_epq_active == NULL)
    {
        if (estate->es_result_relations == NULL ||
            estate->es_result_relations[node->resultRelation - 1] == NULL)
        {
            elog(ERROR, "result relation not initialized");
        }
        scanstate->resultRelInfo = estate->es_result_relations[node->resultRelation - 1];
    }
 
    /* Initialize any outer plan. */
    if (outerPlan(node))
        outerPlanState(scanstate) =
            ExecInitNode(outerPlan(node), estate, eflags);
 
    /*
     * Tell the FDW to initialize the scan.
     */
    if (node->operation != CMD_SELECT)
    {
        /*
         * Direct modifications cannot be re-evaluated by EvalPlanQual, so
         * don't bother preparing the FDW.
         *
         * In case of an inherited UPDATE/DELETE with foreign targets there
         * can be direct-modify ForeignScan nodes in the EvalPlanQual subtree,
         * so we need to ignore such ForeignScan nodes during EvalPlanQual
         * processing.  See also ExecForeignScan/ExecReScanForeignScan.
         */
        if (estate->es_epq_active == NULL)
            fdwroutine->BeginDirectModify(scanstate, eflags);
    }
    else
        fdwroutine->BeginForeignScan(scanstate, eflags);
 
    return scanstate;
}
 
/* ----------------------------------------------------------------
 *      ExecEndForeignScan
 *
 *      frees any storage allocated through C routines.
 * ----------------------------------------------------------------
 */
void
ExecEndForeignScan(ForeignScanState *node)
{
    ForeignScan *plan = (ForeignScan *) node->ss.ps.plan;
    EState     *estate = node->ss.ps.state;
 
    /* Let the FDW shut down */
    if (plan->operation != CMD_SELECT)
    {
        if (estate->es_epq_active == NULL)
            node->fdwroutine->EndDirectModify(node);
    }
    else
        node->fdwroutine->EndForeignScan(node);
 
    /* Shut down any outer plan. */
    if (outerPlanState(node))
        ExecEndNode(outerPlanState(node));
}
 
/* ----------------------------------------------------------------
 *      ExecReScanForeignScan
 *
 *      Rescans the relation.
 * ----------------------------------------------------------------
 */
void
ExecReScanForeignScan(ForeignScanState *node)
{
    ForeignScan *plan = (ForeignScan *) node->ss.ps.plan;
    EState     *estate = node->ss.ps.state;
    PlanState  *outerPlan = outerPlanState(node);
 
    /*
     * Ignore direct modifications when EvalPlanQual is active --- they are
     * irrelevant for EvalPlanQual rechecking
     */
    if (estate->es_epq_active != NULL && plan->operation != CMD_SELECT)
        return;
 
    node->fdwroutine->ReScanForeignScan(node);
 
    /*
     * If chgParam of subnode is not null then plan will be re-scanned by
     * first ExecProcNode.  outerPlan may also be NULL, in which case there is
     * nothing to rescan at all.
     */
    if (outerPlan != NULL && outerPlan->chgParam == NULL)
        ExecReScan(outerPlan);
 
    ExecScanReScan(&node->ss);
}
 
/* ----------------------------------------------------------------
 *      ExecForeignScanEstimate
 *
 *      Informs size of the parallel coordination information, if any
 * ----------------------------------------------------------------
 */
void
ExecForeignScanEstimate(ForeignScanState *node, ParallelContext *pcxt)
{
    FdwRoutine *fdwroutine = node->fdwroutine;
 
    if (fdwroutine->EstimateDSMForeignScan)
    {
        node->pscan_len = fdwroutine->EstimateDSMForeignScan(node, pcxt);
        shm_toc_estimate_chunk(&pcxt->estimator, node->pscan_len);
        shm_toc_estimate_keys(&pcxt->estimator, 1);
    }
}
 
/* ----------------------------------------------------------------
 *      ExecForeignScanInitializeDSM
 *
 *      Initialize the parallel coordination information
 * ----------------------------------------------------------------
 */
void
ExecForeignScanInitializeDSM(ForeignScanState *node, ParallelContext *pcxt)
{
    FdwRoutine *fdwroutine = node->fdwroutine;
 
    if (fdwroutine->InitializeDSMForeignScan)
    {
        int         plan_node_id = node->ss.ps.plan->plan_node_id;
        void       *coordinate;
 
        coordinate = shm_toc_allocate(pcxt->toc, node->pscan_len);
        fdwroutine->InitializeDSMForeignScan(node, pcxt, coordinate);
        shm_toc_insert(pcxt->toc, plan_node_id, coordinate);
    }
}
 
/* ----------------------------------------------------------------
 *      ExecForeignScanReInitializeDSM
 *
 *      Reset shared state before beginning a fresh scan.
 * ----------------------------------------------------------------
 */
void
ExecForeignScanReInitializeDSM(ForeignScanState *node, ParallelContext *pcxt)
{
    FdwRoutine *fdwroutine = node->fdwroutine;
 
    if (fdwroutine->ReInitializeDSMForeignScan)
    {
        int         plan_node_id = node->ss.ps.plan->plan_node_id;
        void       *coordinate;
 
        coordinate = shm_toc_lookup(pcxt->toc, plan_node_id, false);
        fdwroutine->ReInitializeDSMForeignScan(node, pcxt, coordinate);
    }
}
 
/* ----------------------------------------------------------------
 *      ExecForeignScanInitializeWorker
 *
 *      Initialization according to the parallel coordination information
 * ----------------------------------------------------------------
 */
void
ExecForeignScanInitializeWorker(ForeignScanState *node,
                                ParallelWorkerContext *pwcxt)
{
    FdwRoutine *fdwroutine = node->fdwroutine;
 
    if (fdwroutine->InitializeWorkerForeignScan)
    {
        int         plan_node_id = node->ss.ps.plan->plan_node_id;
        void       *coordinate;
 
        coordinate = shm_toc_lookup(pwcxt->toc, plan_node_id, false);
        fdwroutine->InitializeWorkerForeignScan(node, pwcxt->toc, coordinate);
    }
}
 
/* ----------------------------------------------------------------
 *      ExecShutdownForeignScan
 *
 *      Gives FDW chance to stop asynchronous resource consumption
 *      and release any resources still held.
 * ----------------------------------------------------------------
 */
void
ExecShutdownForeignScan(ForeignScanState *node)
{
    FdwRoutine *fdwroutine = node->fdwroutine;
 
    if (fdwroutine->ShutdownForeignScan)
        fdwroutine->ShutdownForeignScan(node);
}
 
/* ----------------------------------------------------------------
 *      ExecAsyncForeignScanRequest
 *
 *      Asynchronously request a tuple from a designed async-capable node
 * ----------------------------------------------------------------
 */
void
ExecAsyncForeignScanRequest(AsyncRequest *areq)
{
    ForeignScanState *node = (ForeignScanState *) areq->requestee;
    FdwRoutine *fdwroutine = node->fdwroutine;
 
    Assert(fdwroutine->ForeignAsyncRequest != NULL);
    fdwroutine->ForeignAsyncRequest(areq);
}
 
/* ----------------------------------------------------------------
 *      ExecAsyncForeignScanConfigureWait
 *
 *      In async mode, configure for a wait
 * ----------------------------------------------------------------
 */
void
ExecAsyncForeignScanConfigureWait(AsyncRequest *areq)
{
    ForeignScanState *node = (ForeignScanState *) areq->requestee;
    FdwRoutine *fdwroutine = node->fdwroutine;
 
    Assert(fdwroutine->ForeignAsyncConfigureWait != NULL);
    fdwroutine->ForeignAsyncConfigureWait(areq);
}
 
/* ----------------------------------------------------------------
 *      ExecAsyncForeignScanNotify
 *
 *      Callback invoked when a relevant event has occurred
 * ----------------------------------------------------------------
 */
void
ExecAsyncForeignScanNotify(AsyncRequest *areq)
{
    ForeignScanState *node = (ForeignScanState *) areq->requestee;
    FdwRoutine *fdwroutine = node->fdwroutine;
 
    Assert(fdwroutine->ForeignAsyncNotify != NULL);
    fdwroutine->ForeignAsyncNotify(areq);
}