nodeSeqscan.c

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/*-------------------------------------------------------------------------
 *
 * nodeSeqscan.c
 *    Support routines for sequential scans of relations.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeSeqscan.c
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *      ExecSeqScan             sequentially scans a relation.
 *      ExecSeqNext             retrieve next tuple in sequential order.
 *      ExecInitSeqScan         creates and initializes a seqscan node.
 *      ExecEndSeqScan          releases any storage allocated.
 *      ExecReScanSeqScan       rescans the relation
 *
 *      ExecSeqScanEstimate     estimates DSM space needed for parallel scan
 *      ExecSeqScanInitializeDSM initialize DSM for parallel scan
 *      ExecSeqScanReInitializeDSM reinitialize DSM for fresh parallel scan
 *      ExecSeqScanInitializeWorker attach to DSM info in parallel worker
 */
#include "postgres.h"
 
#include "access/relscan.h"
#include "access/tableam.h"
#include "executor/execScan.h"
#include "executor/executor.h"
#include "executor/nodeSeqscan.h"
#include "utils/rel.h"
 
static TupleTableSlot *SeqNext(SeqScanState *node);
 
/* ----------------------------------------------------------------
 *                      Scan Support
 * ----------------------------------------------------------------
 */
 
/* ----------------------------------------------------------------
 *      SeqNext
 *
 *      This is a workhorse for ExecSeqScan
 * ----------------------------------------------------------------
 */
static pg_attribute_always_inline TupleTableSlot *
SeqNext(SeqScanState *node)
{
    TableScanDesc scandesc;
    EState     *estate;
    ScanDirection direction;
    TupleTableSlot *slot;
 
    /*
     * get information from the estate and scan state
     */
    scandesc = node->ss.ss_currentScanDesc;
    estate = node->ss.ps.state;
    direction = estate->es_direction;
    slot = node->ss.ss_ScanTupleSlot;
 
    if (scandesc == NULL)
    {
        /*
         * We reach here if the scan is not parallel, or if we're serially
         * executing a scan that was planned to be parallel.
         */
        scandesc = table_beginscan(node->ss.ss_currentRelation,
                                   estate->es_snapshot,
                                   0, NULL);
        node->ss.ss_currentScanDesc = scandesc;
    }
 
    /*
     * get the next tuple from the table
     */
    if (table_scan_getnextslot(scandesc, direction, slot))
        return slot;
    return NULL;
}
 
/*
 * SeqRecheck -- access method routine to recheck a tuple in EvalPlanQual
 */
static pg_attribute_always_inline bool
SeqRecheck(SeqScanState *node, TupleTableSlot *slot)
{
    /*
     * Note that unlike IndexScan, SeqScan never use keys in heap_beginscan
     * (and this is very bad) - so, here we do not check are keys ok or not.
     */
    return true;
}
 
/* ----------------------------------------------------------------
 *      ExecSeqScan(node)
 *
 *      Scans the relation sequentially and returns the next qualifying
 *      tuple. This variant is used when there is no es_epq_active, no qual
 *      and no projection.  Passing const-NULLs for these to ExecScanExtended
 *      allows the compiler to eliminate the additional code that would
 *      ordinarily be required for the evaluation of these.
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecSeqScan(PlanState *pstate)
{
    SeqScanState *node = castNode(SeqScanState, pstate);
 
    Assert(pstate->state->es_epq_active == NULL);
    Assert(pstate->qual == NULL);
    Assert(pstate->ps_ProjInfo == NULL);
 
    return ExecScanExtended(&node->ss,
                            (ExecScanAccessMtd) SeqNext,
                            (ExecScanRecheckMtd) SeqRecheck,
                            NULL,
                            NULL,
                            NULL);
}
 
/*
 * Variant of ExecSeqScan() but when qual evaluation is required.
 */
static TupleTableSlot *
ExecSeqScanWithQual(PlanState *pstate)
{
    SeqScanState *node = castNode(SeqScanState, pstate);
 
    /*
     * Use pg_assume() for != NULL tests to make the compiler realize no
     * runtime check for the field is needed in ExecScanExtended().
     */
    Assert(pstate->state->es_epq_active == NULL);
    pg_assume(pstate->qual != NULL);
    Assert(pstate->ps_ProjInfo == NULL);
 
    return ExecScanExtended(&node->ss,
                            (ExecScanAccessMtd) SeqNext,
                            (ExecScanRecheckMtd) SeqRecheck,
                            NULL,
                            pstate->qual,
                            NULL);
}
 
/*
 * Variant of ExecSeqScan() but when projection is required.
 */
static TupleTableSlot *
ExecSeqScanWithProject(PlanState *pstate)
{
    SeqScanState *node = castNode(SeqScanState, pstate);
 
    Assert(pstate->state->es_epq_active == NULL);
    Assert(pstate->qual == NULL);
    pg_assume(pstate->ps_ProjInfo != NULL);
 
    return ExecScanExtended(&node->ss,
                            (ExecScanAccessMtd) SeqNext,
                            (ExecScanRecheckMtd) SeqRecheck,
                            NULL,
                            NULL,
                            pstate->ps_ProjInfo);
}
 
/*
 * Variant of ExecSeqScan() but when qual evaluation and projection are
 * required.
 */
static TupleTableSlot *
ExecSeqScanWithQualProject(PlanState *pstate)
{
    SeqScanState *node = castNode(SeqScanState, pstate);
 
    Assert(pstate->state->es_epq_active == NULL);
    pg_assume(pstate->qual != NULL);
    pg_assume(pstate->ps_ProjInfo != NULL);
 
    return ExecScanExtended(&node->ss,
                            (ExecScanAccessMtd) SeqNext,
                            (ExecScanRecheckMtd) SeqRecheck,
                            NULL,
                            pstate->qual,
                            pstate->ps_ProjInfo);
}
 
/*
 * Variant of ExecSeqScan for when EPQ evaluation is required.  We don't
 * bother adding variants of this for with/without qual and projection as
 * EPQ doesn't seem as exciting a case to optimize for.
 */
static TupleTableSlot *
ExecSeqScanEPQ(PlanState *pstate)
{
    SeqScanState *node = castNode(SeqScanState, pstate);
 
    return ExecScan(&node->ss,
                    (ExecScanAccessMtd) SeqNext,
                    (ExecScanRecheckMtd) SeqRecheck);
}
 
/* ----------------------------------------------------------------
 *      ExecInitSeqScan
 * ----------------------------------------------------------------
 */
SeqScanState *
ExecInitSeqScan(SeqScan *node, EState *estate, int eflags)
{
    SeqScanState *scanstate;
 
    /*
     * Once upon a time it was possible to have an outerPlan of a SeqScan, but
     * not any more.
     */
    Assert(outerPlan(node) == NULL);
    Assert(innerPlan(node) == NULL);
 
    /*
     * create state structure
     */
    scanstate = makeNode(SeqScanState);
    scanstate->ss.ps.plan = (Plan *) node;
    scanstate->ss.ps.state = estate;
 
    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &scanstate->ss.ps);
 
    /*
     * open the scan relation
     */
    scanstate->ss.ss_currentRelation =
        ExecOpenScanRelation(estate,
                             node->scan.scanrelid,
                             eflags);
 
    /* and create slot with the appropriate rowtype */
    ExecInitScanTupleSlot(estate, &scanstate->ss,
                          RelationGetDescr(scanstate->ss.ss_currentRelation),
                          table_slot_callbacks(scanstate->ss.ss_currentRelation));
 
    /*
     * Initialize result type and projection.
     */
    ExecInitResultTypeTL(&scanstate->ss.ps);
    ExecAssignScanProjectionInfo(&scanstate->ss);
 
    /*
     * initialize child expressions
     */
    scanstate->ss.ps.qual =
        ExecInitQual(node->scan.plan.qual, (PlanState *) scanstate);
 
    /*
     * When EvalPlanQual() is not in use, assign ExecProcNode for this node
     * based on the presence of qual and projection. Each ExecSeqScan*()
     * variant is optimized for the specific combination of these conditions.
     */
    if (scanstate->ss.ps.state->es_epq_active != NULL)
        scanstate->ss.ps.ExecProcNode = ExecSeqScanEPQ;
    else if (scanstate->ss.ps.qual == NULL)
    {
        if (scanstate->ss.ps.ps_ProjInfo == NULL)
            scanstate->ss.ps.ExecProcNode = ExecSeqScan;
        else
            scanstate->ss.ps.ExecProcNode = ExecSeqScanWithProject;
    }
    else
    {
        if (scanstate->ss.ps.ps_ProjInfo == NULL)
            scanstate->ss.ps.ExecProcNode = ExecSeqScanWithQual;
        else
            scanstate->ss.ps.ExecProcNode = ExecSeqScanWithQualProject;
    }
 
    return scanstate;
}
 
/* ----------------------------------------------------------------
 *      ExecEndSeqScan
 *
 *      frees any storage allocated through C routines.
 * ----------------------------------------------------------------
 */
void
ExecEndSeqScan(SeqScanState *node)
{
    TableScanDesc scanDesc;
 
    /*
     * get information from node
     */
    scanDesc = node->ss.ss_currentScanDesc;
 
    /*
     * close heap scan
     */
    if (scanDesc != NULL)
        table_endscan(scanDesc);
}
 
/* ----------------------------------------------------------------
 *                      Join Support
 * ----------------------------------------------------------------
 */
 
/* ----------------------------------------------------------------
 *      ExecReScanSeqScan
 *
 *      Rescans the relation.
 * ----------------------------------------------------------------
 */
void
ExecReScanSeqScan(SeqScanState *node)
{
    TableScanDesc scan;
 
    scan = node->ss.ss_currentScanDesc;
 
    if (scan != NULL)
        table_rescan(scan,      /* scan desc */
                     NULL);     /* new scan keys */
 
    ExecScanReScan((ScanState *) node);
}
 
/* ----------------------------------------------------------------
 *                      Parallel Scan Support
 * ----------------------------------------------------------------
 */
 
/* ----------------------------------------------------------------
 *      ExecSeqScanEstimate
 *
 *      Compute the amount of space we'll need in the parallel
 *      query DSM, and inform pcxt->estimator about our needs.
 * ----------------------------------------------------------------
 */
void
ExecSeqScanEstimate(SeqScanState *node,
                    ParallelContext *pcxt)
{
    EState     *estate = node->ss.ps.state;
 
    node->pscan_len = table_parallelscan_estimate(node->ss.ss_currentRelation,
                                                  estate->es_snapshot);
    shm_toc_estimate_chunk(&pcxt->estimator, node->pscan_len);
    shm_toc_estimate_keys(&pcxt->estimator, 1);
}
 
/* ----------------------------------------------------------------
 *      ExecSeqScanInitializeDSM
 *
 *      Set up a parallel heap scan descriptor.
 * ----------------------------------------------------------------
 */
void
ExecSeqScanInitializeDSM(SeqScanState *node,
                         ParallelContext *pcxt)
{
    EState     *estate = node->ss.ps.state;
    ParallelTableScanDesc pscan;
 
    pscan = shm_toc_allocate(pcxt->toc, node->pscan_len);
    table_parallelscan_initialize(node->ss.ss_currentRelation,
                                  pscan,
                                  estate->es_snapshot);
    shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id, pscan);
    node->ss.ss_currentScanDesc =
        table_beginscan_parallel(node->ss.ss_currentRelation, pscan);
}
 
/* ----------------------------------------------------------------
 *      ExecSeqScanReInitializeDSM
 *
 *      Reset shared state before beginning a fresh scan.
 * ----------------------------------------------------------------
 */
void
ExecSeqScanReInitializeDSM(SeqScanState *node,
                           ParallelContext *pcxt)
{
    ParallelTableScanDesc pscan;
 
    pscan = node->ss.ss_currentScanDesc->rs_parallel;
    table_parallelscan_reinitialize(node->ss.ss_currentRelation, pscan);
}
 
/* ----------------------------------------------------------------
 *      ExecSeqScanInitializeWorker
 *
 *      Copy relevant information from TOC into planstate.
 * ----------------------------------------------------------------
 */
void
ExecSeqScanInitializeWorker(SeqScanState *node,
                            ParallelWorkerContext *pwcxt)
{
    ParallelTableScanDesc pscan;
 
    pscan = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
    node->ss.ss_currentScanDesc =
        table_beginscan_parallel(node->ss.ss_currentRelation, pscan);
}