execAmi.c

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/*-------------------------------------------------------------------------
 *
 * execAmi.c
 *    miscellaneous executor access method routines
 *
 * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *  src/backend/executor/execAmi.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/amapi.h"
#include "access/htup_details.h"
#include "executor/execdebug.h"
#include "executor/nodeAgg.h"
#include "executor/nodeAppend.h"
#include "executor/nodeBitmapAnd.h"
#include "executor/nodeBitmapHeapscan.h"
#include "executor/nodeBitmapIndexscan.h"
#include "executor/nodeBitmapOr.h"
#include "executor/nodeCtescan.h"
#include "executor/nodeCustom.h"
#include "executor/nodeForeignscan.h"
#include "executor/nodeFunctionscan.h"
#include "executor/nodeGather.h"
#include "executor/nodeGatherMerge.h"
#include "executor/nodeGroup.h"
#include "executor/nodeHash.h"
#include "executor/nodeHashjoin.h"
#include "executor/nodeIndexonlyscan.h"
#include "executor/nodeIndexscan.h"
#include "executor/nodeLimit.h"
#include "executor/nodeLockRows.h"
#include "executor/nodeMaterial.h"
#include "executor/nodeMergeAppend.h"
#include "executor/nodeMergejoin.h"
#include "executor/nodeModifyTable.h"
#include "executor/nodeNamedtuplestorescan.h"
#include "executor/nodeNestloop.h"
#include "executor/nodeProjectSet.h"
#include "executor/nodeRecursiveunion.h"
#include "executor/nodeResult.h"
#include "executor/nodeSamplescan.h"
#include "executor/nodeSeqscan.h"
#include "executor/nodeSetOp.h"
#include "executor/nodeSort.h"
#include "executor/nodeSubplan.h"
#include "executor/nodeSubqueryscan.h"
#include "executor/nodeTableFuncscan.h"
#include "executor/nodeTidscan.h"
#include "executor/nodeUnique.h"
#include "executor/nodeValuesscan.h"
#include "executor/nodeWindowAgg.h"
#include "executor/nodeWorktablescan.h"
#include "nodes/extensible.h"
#include "nodes/nodeFuncs.h"
#include "nodes/pathnodes.h"
#include "utils/rel.h"
#include "utils/syscache.h"

static bool IndexSupportsBackwardScan(Oid indexid);


/*
 * ExecReScan
 *      Reset a plan node so that its output can be re-scanned.
 *
 * Note that if the plan node has parameters that have changed value,
 * the output might be different from last time.
 */
void
ExecReScan(PlanState *node)
{
    /* If collecting timing stats, update them */
    if (node->instrument)
        InstrEndLoop(node->instrument);

    /*
     * If we have changed parameters, propagate that info.
     *
     * Note: ExecReScanSetParamPlan() can add bits to node->chgParam,
     * corresponding to the output param(s) that the InitPlan will update.
     * Since we make only one pass over the list, that means that an InitPlan
     * can depend on the output param(s) of a sibling InitPlan only if that
     * sibling appears earlier in the list.  This is workable for now given
     * the limited ways in which one InitPlan could depend on another, but
     * eventually we might need to work harder (or else make the planner
     * enlarge the extParam/allParam sets to include the params of depended-on
     * InitPlans).
     */
    if (node->chgParam != NULL)
    {
        ListCell   *l;

        foreach(l, node->initPlan)
        {
            SubPlanState *sstate = (SubPlanState *) lfirst(l);
            PlanState  *splan = sstate->planstate;

            if (splan->plan->extParam != NULL)  /* don't care about child
                                                 * local Params */
                UpdateChangedParamSet(splan, node->chgParam);
            if (splan->chgParam != NULL)
                ExecReScanSetParamPlan(sstate, node);
        }
        foreach(l, node->subPlan)
        {
            SubPlanState *sstate = (SubPlanState *) lfirst(l);
            PlanState  *splan = sstate->planstate;

            if (splan->plan->extParam != NULL)
                UpdateChangedParamSet(splan, node->chgParam);
        }
        /* Well. Now set chgParam for left/right trees. */
        if (node->lefttree != NULL)
            UpdateChangedParamSet(node->lefttree, node->chgParam);
        if (node->righttree != NULL)
            UpdateChangedParamSet(node->righttree, node->chgParam);
    }

    /* Call expression callbacks */
    if (node->ps_ExprContext)
        ReScanExprContext(node->ps_ExprContext);

    /* And do node-type-specific processing */
    switch (nodeTag(node))
    {
        case T_ResultState:
            ExecReScanResult((ResultState *) node);
            break;

        case T_ProjectSetState:
            ExecReScanProjectSet((ProjectSetState *) node);
            break;

        case T_ModifyTableState:
            ExecReScanModifyTable((ModifyTableState *) node);
            break;

        case T_AppendState:
            ExecReScanAppend((AppendState *) node);
            break;

        case T_MergeAppendState:
            ExecReScanMergeAppend((MergeAppendState *) node);
            break;

        case T_RecursiveUnionState:
            ExecReScanRecursiveUnion((RecursiveUnionState *) node);
            break;

        case T_BitmapAndState:
            ExecReScanBitmapAnd((BitmapAndState *) node);
            break;

        case T_BitmapOrState:
            ExecReScanBitmapOr((BitmapOrState *) node);
            break;

        case T_SeqScanState:
            ExecReScanSeqScan((SeqScanState *) node);
            break;

        case T_SampleScanState:
            ExecReScanSampleScan((SampleScanState *) node);
            break;

        case T_GatherState:
            ExecReScanGather((GatherState *) node);
            break;

        case T_GatherMergeState:
            ExecReScanGatherMerge((GatherMergeState *) node);
            break;

        case T_IndexScanState:
            ExecReScanIndexScan((IndexScanState *) node);
            break;

        case T_IndexOnlyScanState:
            ExecReScanIndexOnlyScan((IndexOnlyScanState *) node);
            break;

        case T_BitmapIndexScanState:
            ExecReScanBitmapIndexScan((BitmapIndexScanState *) node);
            break;

        case T_BitmapHeapScanState:
            ExecReScanBitmapHeapScan((BitmapHeapScanState *) node);
            break;

        case T_TidScanState:
            ExecReScanTidScan((TidScanState *) node);
            break;

        case T_SubqueryScanState:
            ExecReScanSubqueryScan((SubqueryScanState *) node);
            break;

        case T_FunctionScanState:
            ExecReScanFunctionScan((FunctionScanState *) node);
            break;

        case T_TableFuncScanState:
            ExecReScanTableFuncScan((TableFuncScanState *) node);
            break;

        case T_ValuesScanState:
            ExecReScanValuesScan((ValuesScanState *) node);
            break;

        case T_CteScanState:
            ExecReScanCteScan((CteScanState *) node);
            break;

        case T_NamedTuplestoreScanState:
            ExecReScanNamedTuplestoreScan((NamedTuplestoreScanState *) node);
            break;

        case T_WorkTableScanState:
            ExecReScanWorkTableScan((WorkTableScanState *) node);
            break;

        case T_ForeignScanState:
            ExecReScanForeignScan((ForeignScanState *) node);
            break;

        case T_CustomScanState:
            ExecReScanCustomScan((CustomScanState *) node);
            break;

        case T_NestLoopState:
            ExecReScanNestLoop((NestLoopState *) node);
            break;

        case T_MergeJoinState:
            ExecReScanMergeJoin((MergeJoinState *) node);
            break;

        case T_HashJoinState:
            ExecReScanHashJoin((HashJoinState *) node);
            break;

        case T_MaterialState:
            ExecReScanMaterial((MaterialState *) node);
            break;

        case T_SortState:
            ExecReScanSort((SortState *) node);
            break;

        case T_GroupState:
            ExecReScanGroup((GroupState *) node);
            break;

        case T_AggState:
            ExecReScanAgg((AggState *) node);
            break;

        case T_WindowAggState:
            ExecReScanWindowAgg((WindowAggState *) node);
            break;

        case T_UniqueState:
            ExecReScanUnique((UniqueState *) node);
            break;

        case T_HashState:
            ExecReScanHash((HashState *) node);
            break;

        case T_SetOpState:
            ExecReScanSetOp((SetOpState *) node);
            break;

        case T_LockRowsState:
            ExecReScanLockRows((LockRowsState *) node);
            break;

        case T_LimitState:
            ExecReScanLimit((LimitState *) node);
            break;

        default:
            elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node));
            break;
    }

    if (node->chgParam != NULL)
    {
        bms_free(node->chgParam);
        node->chgParam = NULL;
    }
}

/*
 * ExecMarkPos
 *
 * Marks the current scan position.
 *
 * NOTE: mark/restore capability is currently needed only for plan nodes
 * that are the immediate inner child of a MergeJoin node.  Since MergeJoin
 * requires sorted input, there is never any need to support mark/restore in
 * node types that cannot produce sorted output.  There are some cases in
 * which a node can pass through sorted data from its child; if we don't
 * implement mark/restore for such a node type, the planner compensates by
 * inserting a Material node above that node.
 */
void
ExecMarkPos(PlanState *node)
{
    switch (nodeTag(node))
    {
        case T_IndexScanState:
            ExecIndexMarkPos((IndexScanState *) node);
            break;

        case T_IndexOnlyScanState:
            ExecIndexOnlyMarkPos((IndexOnlyScanState *) node);
            break;

        case T_CustomScanState:
            ExecCustomMarkPos((CustomScanState *) node);
            break;

        case T_MaterialState:
            ExecMaterialMarkPos((MaterialState *) node);
            break;

        case T_SortState:
            ExecSortMarkPos((SortState *) node);
            break;

        case T_ResultState:
            ExecResultMarkPos((ResultState *) node);
            break;

        default:
            /* don't make hard error unless caller asks to restore... */
            elog(DEBUG2, "unrecognized node type: %d", (int) nodeTag(node));
            break;
    }
}

/*
 * ExecRestrPos
 *
 * restores the scan position previously saved with ExecMarkPos()
 *
 * NOTE: the semantics of this are that the first ExecProcNode following
 * the restore operation will yield the same tuple as the first one following
 * the mark operation.  It is unspecified what happens to the plan node's
 * result TupleTableSlot.  (In most cases the result slot is unchanged by
 * a restore, but the node may choose to clear it or to load it with the
 * restored-to tuple.)  Hence the caller should discard any previously
 * returned TupleTableSlot after doing a restore.
 */
void
ExecRestrPos(PlanState *node)
{
    switch (nodeTag(node))
    {
        case T_IndexScanState:
            ExecIndexRestrPos((IndexScanState *) node);
            break;

        case T_IndexOnlyScanState:
            ExecIndexOnlyRestrPos((IndexOnlyScanState *) node);
            break;

        case T_CustomScanState:
            ExecCustomRestrPos((CustomScanState *) node);
            break;

        case T_MaterialState:
            ExecMaterialRestrPos((MaterialState *) node);
            break;

        case T_SortState:
            ExecSortRestrPos((SortState *) node);
            break;

        case T_ResultState:
            ExecResultRestrPos((ResultState *) node);
            break;

        default:
            elog(ERROR, "unrecognized node type: %d", (int) nodeTag(node));
            break;
    }
}

/*
 * ExecSupportsMarkRestore - does a Path support mark/restore?
 *
 * This is used during planning and so must accept a Path, not a Plan.
 * We keep it here to be adjacent to the routines above, which also must
 * know which plan types support mark/restore.
 */
bool
ExecSupportsMarkRestore(Path *pathnode)
{
    /*
     * For consistency with the routines above, we do not examine the nodeTag
     * but rather the pathtype, which is the Plan node type the Path would
     * produce.
     */
    switch (pathnode->pathtype)
    {
        case T_IndexScan:
        case T_IndexOnlyScan:
        case T_Material:
        case T_Sort:
            return true;

        case T_CustomScan:
            {
                CustomPath *customPath = castNode(CustomPath, pathnode);

                if (customPath->flags & CUSTOMPATH_SUPPORT_MARK_RESTORE)
                    return true;
                return false;
            }
        case T_Result:

            /*
             * Result supports mark/restore iff it has a child plan that does.
             *
             * We have to be careful here because there is more than one Path
             * type that can produce a Result plan node.
             */
            if (IsA(pathnode, ProjectionPath))
                return ExecSupportsMarkRestore(((ProjectionPath *) pathnode)->subpath);
            else if (IsA(pathnode, MinMaxAggPath))
                return false;   /* childless Result */
            else if (IsA(pathnode, GroupResultPath))
                return false;   /* childless Result */
            else
            {
                /* Simple RTE_RESULT base relation */
                Assert(IsA(pathnode, Path));
                return false;   /* childless Result */
            }

        case T_Append:
            {
                AppendPath *appendPath = castNode(AppendPath, pathnode);

                /*
                 * If there's exactly one child, then there will be no Append
                 * in the final plan, so we can handle mark/restore if the
                 * child plan node can.
                 */
                if (list_length(appendPath->subpaths) == 1)
                    return ExecSupportsMarkRestore((Path *) linitial(appendPath->subpaths));
                /* Otherwise, Append can't handle it */
                return false;
            }

        case T_MergeAppend:
            {
                MergeAppendPath *mapath = castNode(MergeAppendPath, pathnode);

                /*
                 * Like the Append case above, single-subpath MergeAppends
                 * won't be in the final plan, so just return the child's
                 * mark/restore ability.
                 */
                if (list_length(mapath->subpaths) == 1)
                    return ExecSupportsMarkRestore((Path *) linitial(mapath->subpaths));
                /* Otherwise, MergeAppend can't handle it */
                return false;
            }

        default:
            break;
    }

    return false;
}

/*
 * ExecSupportsBackwardScan - does a plan type support backwards scanning?
 *
 * Ideally, all plan types would support backwards scan, but that seems
 * unlikely to happen soon.  In some cases, a plan node passes the backwards
 * scan down to its children, and so supports backwards scan only if its
 * children do.  Therefore, this routine must be passed a complete plan tree.
 */
bool
ExecSupportsBackwardScan(Plan *node)
{
    if (node == NULL)
        return false;

    /*
     * Parallel-aware nodes return a subset of the tuples in each worker, and
     * in general we can't expect to have enough bookkeeping state to know
     * which ones we returned in this worker as opposed to some other worker.
     */
    if (node->parallel_aware)
        return false;

    switch (nodeTag(node))
    {
        case T_Result:
            if (outerPlan(node) != NULL)
                return ExecSupportsBackwardScan(outerPlan(node));
            else
                return false;

        case T_Append:
            {
                ListCell   *l;

                foreach(l, ((Append *) node)->appendplans)
                {
                    if (!ExecSupportsBackwardScan((Plan *) lfirst(l)))
                        return false;
                }
                /* need not check tlist because Append doesn't evaluate it */
                return true;
            }

        case T_SampleScan:
            /* Simplify life for tablesample methods by disallowing this */
            return false;

        case T_Gather:
            return false;

        case T_IndexScan:
            return IndexSupportsBackwardScan(((IndexScan *) node)->indexid);

        case T_IndexOnlyScan:
            return IndexSupportsBackwardScan(((IndexOnlyScan *) node)->indexid);

        case T_SubqueryScan:
            return ExecSupportsBackwardScan(((SubqueryScan *) node)->subplan);

        case T_CustomScan:
            {
                uint32      flags = ((CustomScan *) node)->flags;

                if (flags & CUSTOMPATH_SUPPORT_BACKWARD_SCAN)
                    return true;
            }
            return false;

        case T_SeqScan:
        case T_TidScan:
        case T_FunctionScan:
        case T_ValuesScan:
        case T_CteScan:
        case T_Material:
        case T_Sort:
            return true;

        case T_LockRows:
        case T_Limit:
            return ExecSupportsBackwardScan(outerPlan(node));

        default:
            return false;
    }
}

/*
 * An IndexScan or IndexOnlyScan node supports backward scan only if the
 * index's AM does.
 */
static bool
IndexSupportsBackwardScan(Oid indexid)
{
    bool        result;
    HeapTuple   ht_idxrel;
    Form_pg_class idxrelrec;
    IndexAmRoutine *amroutine;

    /* Fetch the pg_class tuple of the index relation */
    ht_idxrel = SearchSysCache1(RELOID, ObjectIdGetDatum(indexid));
    if (!HeapTupleIsValid(ht_idxrel))
        elog(ERROR, "cache lookup failed for relation %u", indexid);
    idxrelrec = (Form_pg_class) GETSTRUCT(ht_idxrel);

    /* Fetch the index AM's API struct */
    amroutine = GetIndexAmRoutineByAmId(idxrelrec->relam, false);

    result = amroutine->amcanbackward;

    pfree(amroutine);
    ReleaseSysCache(ht_idxrel);

    return result;
}

/*
 * ExecMaterializesOutput - does a plan type materialize its output?
 *
 * Returns true if the plan node type is one that automatically materializes
 * its output (typically by keeping it in a tuplestore).  For such plans,
 * a rescan without any parameter change will have zero startup cost and
 * very low per-tuple cost.
 */
bool
ExecMaterializesOutput(NodeTag plantype)
{
    switch (plantype)
    {
        case T_Material:
        case T_FunctionScan:
        case T_TableFuncScan:
        case T_CteScan:
        case T_NamedTuplestoreScan:
        case T_WorkTableScan:
        case T_Sort:
            return true;

        default:
            break;
    }

    return false;
}