nodeBitmapHeapscan.c

Go to the documentation of this file.

/*-------------------------------------------------------------------------
 *
 * nodeBitmapHeapscan.c
 *    Routines to support bitmapped scans of relations
 *
 * NOTE: it is critical that this plan type only be used with MVCC-compliant
 * snapshots (ie, regular snapshots, not SnapshotAny or one of the other
 * special snapshots).  The reason is that since index and heap scans are
 * decoupled, there can be no assurance that the index tuple prompting a
 * visit to a particular heap TID still exists when the visit is made.
 * Therefore the tuple might not exist anymore either (which is OK because
 * heap_fetch will cope) --- but worse, the tuple slot could have been
 * re-used for a newer tuple.  With an MVCC snapshot the newer tuple is
 * certain to fail the time qual and so it will not be mistakenly returned,
 * but with anything else we might return a tuple that doesn't meet the
 * required index qual conditions.
 *
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/executor/nodeBitmapHeapscan.c
 *
 *-------------------------------------------------------------------------
 */
/*
 * INTERFACE ROUTINES
 *      ExecBitmapHeapScan          scans a relation using bitmap info
 *      ExecBitmapHeapNext          workhorse for above
 *      ExecInitBitmapHeapScan      creates and initializes state info.
 *      ExecReScanBitmapHeapScan    prepares to rescan the plan.
 *      ExecEndBitmapHeapScan       releases all storage.
 */
#include "postgres.h"
 
#include "access/relscan.h"
#include "access/tableam.h"
#include "access/visibilitymap.h"
#include "executor/executor.h"
#include "executor/nodeBitmapHeapscan.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/bufmgr.h"
#include "utils/rel.h"
#include "utils/spccache.h"
 
static void BitmapTableScanSetup(BitmapHeapScanState *node);
static TupleTableSlot *BitmapHeapNext(BitmapHeapScanState *node);
static inline void BitmapDoneInitializingSharedState(ParallelBitmapHeapState *pstate);
static bool BitmapShouldInitializeSharedState(ParallelBitmapHeapState *pstate);
 
 
/*
 * Do the underlying index scan, build the bitmap, set up the parallel state
 * needed for parallel workers to iterate through the bitmap, and set up the
 * underlying table scan descriptor.
 */
static void
BitmapTableScanSetup(BitmapHeapScanState *node)
{
    TBMIterator tbmiterator = {0};
    ParallelBitmapHeapState *pstate = node->pstate;
    dsa_area   *dsa = node->ss.ps.state->es_query_dsa;
 
    if (!pstate)
    {
        node->tbm = (TIDBitmap *) MultiExecProcNode(outerPlanState(node));
 
        if (!node->tbm || !IsA(node->tbm, TIDBitmap))
            elog(ERROR, "unrecognized result from subplan");
    }
    else if (BitmapShouldInitializeSharedState(pstate))
    {
        /*
         * The leader will immediately come out of the function, but others
         * will be blocked until leader populates the TBM and wakes them up.
         */
        node->tbm = (TIDBitmap *) MultiExecProcNode(outerPlanState(node));
        if (!node->tbm || !IsA(node->tbm, TIDBitmap))
            elog(ERROR, "unrecognized result from subplan");
 
        /*
         * Prepare to iterate over the TBM. This will return the dsa_pointer
         * of the iterator state which will be used by multiple processes to
         * iterate jointly.
         */
        pstate->tbmiterator = tbm_prepare_shared_iterate(node->tbm);
 
        /* We have initialized the shared state so wake up others. */
        BitmapDoneInitializingSharedState(pstate);
    }
 
    tbmiterator = tbm_begin_iterate(node->tbm, dsa,
                                    pstate ?
                                    pstate->tbmiterator :
                                    InvalidDsaPointer);
 
    /*
     * If this is the first scan of the underlying table, create the table
     * scan descriptor and begin the scan.
     */
    if (!node->ss.ss_currentScanDesc)
    {
        node->ss.ss_currentScanDesc =
            table_beginscan_bm(node->ss.ss_currentRelation,
                               node->ss.ps.state->es_snapshot,
                               0,
                               NULL);
    }
 
    node->ss.ss_currentScanDesc->st.rs_tbmiterator = tbmiterator;
    node->initialized = true;
}
 
/* ----------------------------------------------------------------
 *      BitmapHeapNext
 *
 *      Retrieve next tuple from the BitmapHeapScan node's currentRelation
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
BitmapHeapNext(BitmapHeapScanState *node)
{
    ExprContext *econtext = node->ss.ps.ps_ExprContext;
    TupleTableSlot *slot = node->ss.ss_ScanTupleSlot;
 
    /*
     * If we haven't yet performed the underlying index scan, do it, and begin
     * the iteration over the bitmap.
     */
    if (!node->initialized)
        BitmapTableScanSetup(node);
 
    while (table_scan_bitmap_next_tuple(node->ss.ss_currentScanDesc,
                                        slot, &node->recheck,
                                        &node->stats.lossy_pages,
                                        &node->stats.exact_pages))
    {
        /*
         * Continuing in previously obtained page.
         */
        CHECK_FOR_INTERRUPTS();
 
        /*
         * If we are using lossy info, we have to recheck the qual conditions
         * at every tuple.
         */
        if (node->recheck)
        {
            econtext->ecxt_scantuple = slot;
            if (!ExecQualAndReset(node->bitmapqualorig, econtext))
            {
                /* Fails recheck, so drop it and loop back for another */
                InstrCountFiltered2(node, 1);
                ExecClearTuple(slot);
                continue;
            }
        }
 
        /* OK to return this tuple */
        return slot;
    }
 
    /*
     * if we get here it means we are at the end of the scan..
     */
    return ExecClearTuple(slot);
}
 
/*
 *  BitmapDoneInitializingSharedState - Shared state is initialized
 *
 *  By this time the leader has already populated the TBM and initialized the
 *  shared state so wake up other processes.
 */
static inline void
BitmapDoneInitializingSharedState(ParallelBitmapHeapState *pstate)
{
    SpinLockAcquire(&pstate->mutex);
    pstate->state = BM_FINISHED;
    SpinLockRelease(&pstate->mutex);
    ConditionVariableBroadcast(&pstate->cv);
}
 
/*
 * BitmapHeapRecheck -- access method routine to recheck a tuple in EvalPlanQual
 */
static bool
BitmapHeapRecheck(BitmapHeapScanState *node, TupleTableSlot *slot)
{
    ExprContext *econtext;
 
    /*
     * extract necessary information from index scan node
     */
    econtext = node->ss.ps.ps_ExprContext;
 
    /* Does the tuple meet the original qual conditions? */
    econtext->ecxt_scantuple = slot;
    return ExecQualAndReset(node->bitmapqualorig, econtext);
}
 
/* ----------------------------------------------------------------
 *      ExecBitmapHeapScan(node)
 * ----------------------------------------------------------------
 */
static TupleTableSlot *
ExecBitmapHeapScan(PlanState *pstate)
{
    BitmapHeapScanState *node = castNode(BitmapHeapScanState, pstate);
 
    return ExecScan(&node->ss,
                    (ExecScanAccessMtd) BitmapHeapNext,
                    (ExecScanRecheckMtd) BitmapHeapRecheck);
}
 
/* ----------------------------------------------------------------
 *      ExecReScanBitmapHeapScan(node)
 * ----------------------------------------------------------------
 */
void
ExecReScanBitmapHeapScan(BitmapHeapScanState *node)
{
    PlanState  *outerPlan = outerPlanState(node);
 
    TableScanDesc scan = node->ss.ss_currentScanDesc;
 
    if (scan)
    {
        /*
         * End iteration on iterators saved in scan descriptor if they have
         * not already been cleaned up.
         */
        if (!tbm_exhausted(&scan->st.rs_tbmiterator))
            tbm_end_iterate(&scan->st.rs_tbmiterator);
 
        /* rescan to release any page pin */
        table_rescan(node->ss.ss_currentScanDesc, NULL);
    }
 
    /* release bitmaps and buffers if any */
    if (node->tbm)
        tbm_free(node->tbm);
    node->tbm = NULL;
    node->initialized = false;
    node->recheck = true;
 
    ExecScanReScan(&node->ss);
 
    /*
     * if chgParam of subnode is not null then plan will be re-scanned by
     * first ExecProcNode.
     */
    if (outerPlan->chgParam == NULL)
        ExecReScan(outerPlan);
}
 
/* ----------------------------------------------------------------
 *      ExecEndBitmapHeapScan
 * ----------------------------------------------------------------
 */
void
ExecEndBitmapHeapScan(BitmapHeapScanState *node)
{
    TableScanDesc scanDesc;
 
    /*
     * When ending a parallel worker, copy the statistics gathered by the
     * worker back into shared memory so that it can be picked up by the main
     * process to report in EXPLAIN ANALYZE.
     */
    if (node->sinstrument != NULL && IsParallelWorker())
    {
        BitmapHeapScanInstrumentation *si;
 
        Assert(ParallelWorkerNumber <= node->sinstrument->num_workers);
        si = &node->sinstrument->sinstrument[ParallelWorkerNumber];
 
        /*
         * Here we accumulate the stats rather than performing memcpy on
         * node->stats into si.  When a Gather/GatherMerge node finishes it
         * will perform planner shutdown on the workers.  On rescan it will
         * spin up new workers which will have a new BitmapHeapScanState and
         * zeroed stats.
         */
        si->exact_pages += node->stats.exact_pages;
        si->lossy_pages += node->stats.lossy_pages;
    }
 
    /*
     * extract information from the node
     */
    scanDesc = node->ss.ss_currentScanDesc;
 
    /*
     * close down subplans
     */
    ExecEndNode(outerPlanState(node));
 
    if (scanDesc)
    {
        /*
         * End iteration on iterators saved in scan descriptor if they have
         * not already been cleaned up.
         */
        if (!tbm_exhausted(&scanDesc->st.rs_tbmiterator))
            tbm_end_iterate(&scanDesc->st.rs_tbmiterator);
 
        /*
         * close table scan
         */
        table_endscan(scanDesc);
    }
 
    /*
     * release bitmaps and buffers if any
     */
    if (node->tbm)
        tbm_free(node->tbm);
}
 
/* ----------------------------------------------------------------
 *      ExecInitBitmapHeapScan
 *
 *      Initializes the scan's state information.
 * ----------------------------------------------------------------
 */
BitmapHeapScanState *
ExecInitBitmapHeapScan(BitmapHeapScan *node, EState *estate, int eflags)
{
    BitmapHeapScanState *scanstate;
    Relation    currentRelation;
 
    /* check for unsupported flags */
    Assert(!(eflags & (EXEC_FLAG_BACKWARD | EXEC_FLAG_MARK)));
 
    /*
     * Assert caller didn't ask for an unsafe snapshot --- see comments at
     * head of file.
     */
    Assert(IsMVCCSnapshot(estate->es_snapshot));
 
    /*
     * create state structure
     */
    scanstate = makeNode(BitmapHeapScanState);
    scanstate->ss.ps.plan = (Plan *) node;
    scanstate->ss.ps.state = estate;
    scanstate->ss.ps.ExecProcNode = ExecBitmapHeapScan;
 
    scanstate->tbm = NULL;
 
    /* Zero the statistics counters */
    memset(&scanstate->stats, 0, sizeof(BitmapHeapScanInstrumentation));
 
    scanstate->initialized = false;
    scanstate->pstate = NULL;
    scanstate->recheck = true;
 
    /*
     * Miscellaneous initialization
     *
     * create expression context for node
     */
    ExecAssignExprContext(estate, &scanstate->ss.ps);
 
    /*
     * open the scan relation
     */
    currentRelation = ExecOpenScanRelation(estate, node->scan.scanrelid, eflags);
 
    /*
     * initialize child nodes
     */
    outerPlanState(scanstate) = ExecInitNode(outerPlan(node), estate, eflags);
 
    /*
     * get the scan type from the relation descriptor.
     */
    ExecInitScanTupleSlot(estate, &scanstate->ss,
                          RelationGetDescr(currentRelation),
                          table_slot_callbacks(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);
    scanstate->bitmapqualorig =
        ExecInitQual(node->bitmapqualorig, (PlanState *) scanstate);
 
    scanstate->ss.ss_currentRelation = currentRelation;
 
    /*
     * all done.
     */
    return scanstate;
}
 
/*----------------
 *      BitmapShouldInitializeSharedState
 *
 *      The first process to come here and see the state to the BM_INITIAL
 *      will become the leader for the parallel bitmap scan and will be
 *      responsible for populating the TIDBitmap.  The other processes will
 *      be blocked by the condition variable until the leader wakes them up.
 * ---------------
 */
static bool
BitmapShouldInitializeSharedState(ParallelBitmapHeapState *pstate)
{
    SharedBitmapState state;
 
    while (1)
    {
        SpinLockAcquire(&pstate->mutex);
        state = pstate->state;
        if (pstate->state == BM_INITIAL)
            pstate->state = BM_INPROGRESS;
        SpinLockRelease(&pstate->mutex);
 
        /* Exit if bitmap is done, or if we're the leader. */
        if (state != BM_INPROGRESS)
            break;
 
        /* Wait for the leader to wake us up. */
        ConditionVariableSleep(&pstate->cv, WAIT_EVENT_PARALLEL_BITMAP_SCAN);
    }
 
    ConditionVariableCancelSleep();
 
    return (state == BM_INITIAL);
}
 
/* ----------------------------------------------------------------
 *      ExecBitmapHeapEstimate
 *
 *      Compute the amount of space we'll need in the parallel
 *      query DSM, and inform pcxt->estimator about our needs.
 * ----------------------------------------------------------------
 */
void
ExecBitmapHeapEstimate(BitmapHeapScanState *node,
                       ParallelContext *pcxt)
{
    Size        size;
 
    size = MAXALIGN(sizeof(ParallelBitmapHeapState));
 
    /* account for instrumentation, if required */
    if (node->ss.ps.instrument && pcxt->nworkers > 0)
    {
        size = add_size(size, offsetof(SharedBitmapHeapInstrumentation, sinstrument));
        size = add_size(size, mul_size(pcxt->nworkers, sizeof(BitmapHeapScanInstrumentation)));
    }
 
    shm_toc_estimate_chunk(&pcxt->estimator, size);
    shm_toc_estimate_keys(&pcxt->estimator, 1);
}
 
/* ----------------------------------------------------------------
 *      ExecBitmapHeapInitializeDSM
 *
 *      Set up a parallel bitmap heap scan descriptor.
 * ----------------------------------------------------------------
 */
void
ExecBitmapHeapInitializeDSM(BitmapHeapScanState *node,
                            ParallelContext *pcxt)
{
    ParallelBitmapHeapState *pstate;
    SharedBitmapHeapInstrumentation *sinstrument = NULL;
    dsa_area   *dsa = node->ss.ps.state->es_query_dsa;
    char       *ptr;
    Size        size;
 
    /* If there's no DSA, there are no workers; initialize nothing. */
    if (dsa == NULL)
        return;
 
    size = MAXALIGN(sizeof(ParallelBitmapHeapState));
    if (node->ss.ps.instrument && pcxt->nworkers > 0)
    {
        size = add_size(size, offsetof(SharedBitmapHeapInstrumentation, sinstrument));
        size = add_size(size, mul_size(pcxt->nworkers, sizeof(BitmapHeapScanInstrumentation)));
    }
 
    ptr = shm_toc_allocate(pcxt->toc, size);
    pstate = (ParallelBitmapHeapState *) ptr;
    ptr += MAXALIGN(sizeof(ParallelBitmapHeapState));
    if (node->ss.ps.instrument && pcxt->nworkers > 0)
        sinstrument = (SharedBitmapHeapInstrumentation *) ptr;
 
    pstate->tbmiterator = 0;
 
    /* Initialize the mutex */
    SpinLockInit(&pstate->mutex);
    pstate->state = BM_INITIAL;
 
    ConditionVariableInit(&pstate->cv);
 
    if (sinstrument)
    {
        sinstrument->num_workers = pcxt->nworkers;
 
        /* ensure any unfilled slots will contain zeroes */
        memset(sinstrument->sinstrument, 0,
               pcxt->nworkers * sizeof(BitmapHeapScanInstrumentation));
    }
 
    shm_toc_insert(pcxt->toc, node->ss.ps.plan->plan_node_id, pstate);
    node->pstate = pstate;
    node->sinstrument = sinstrument;
}
 
/* ----------------------------------------------------------------
 *      ExecBitmapHeapReInitializeDSM
 *
 *      Reset shared state before beginning a fresh scan.
 * ----------------------------------------------------------------
 */
void
ExecBitmapHeapReInitializeDSM(BitmapHeapScanState *node,
                              ParallelContext *pcxt)
{
    ParallelBitmapHeapState *pstate = node->pstate;
    dsa_area   *dsa = node->ss.ps.state->es_query_dsa;
 
    /* If there's no DSA, there are no workers; do nothing. */
    if (dsa == NULL)
        return;
 
    pstate->state = BM_INITIAL;
 
    if (DsaPointerIsValid(pstate->tbmiterator))
        tbm_free_shared_area(dsa, pstate->tbmiterator);
 
    pstate->tbmiterator = InvalidDsaPointer;
}
 
/* ----------------------------------------------------------------
 *      ExecBitmapHeapInitializeWorker
 *
 *      Copy relevant information from TOC into planstate.
 * ----------------------------------------------------------------
 */
void
ExecBitmapHeapInitializeWorker(BitmapHeapScanState *node,
                               ParallelWorkerContext *pwcxt)
{
    char       *ptr;
 
    Assert(node->ss.ps.state->es_query_dsa != NULL);
 
    ptr = shm_toc_lookup(pwcxt->toc, node->ss.ps.plan->plan_node_id, false);
 
    node->pstate = (ParallelBitmapHeapState *) ptr;
    ptr += MAXALIGN(sizeof(ParallelBitmapHeapState));
 
    if (node->ss.ps.instrument)
        node->sinstrument = (SharedBitmapHeapInstrumentation *) ptr;
}
 
/* ----------------------------------------------------------------
 *      ExecBitmapHeapRetrieveInstrumentation
 *
 *      Transfer bitmap heap scan statistics from DSM to private memory.
 * ----------------------------------------------------------------
 */
void
ExecBitmapHeapRetrieveInstrumentation(BitmapHeapScanState *node)
{
    SharedBitmapHeapInstrumentation *sinstrument = node->sinstrument;
    Size        size;
 
    if (sinstrument == NULL)
        return;
 
    size = offsetof(SharedBitmapHeapInstrumentation, sinstrument)
        + sinstrument->num_workers * sizeof(BitmapHeapScanInstrumentation);
 
    node->sinstrument = palloc(size);
    memcpy(node->sinstrument, sinstrument, size);
}