execAmi.c

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/*-------------------------------------------------------------------------
 *
 * execAmi.c
 *    miscellaneous executor access method routines
 *
 * Portions Copyright (c) 1996-2013, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *  src/backend/executor/execAmi.c
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.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/nodeForeignscan.h"
#include "executor/nodeFunctionscan.h"
#include "executor/nodeGroup.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/nodeNestloop.h"
#include "executor/nodeRecursiveunion.h"
#include "executor/nodeResult.h"
#include "executor/nodeSeqscan.h"
#include "executor/nodeSetOp.h"
#include "executor/nodeSort.h"
#include "executor/nodeSubplan.h"
#include "executor/nodeSubqueryscan.h"
#include "executor/nodeTidscan.h"
#include "executor/nodeUnique.h"
#include "executor/nodeValuesscan.h"
#include "executor/nodeWindowAgg.h"
#include "executor/nodeWorktablescan.h"
#include "nodes/nodeFuncs.h"
#include "utils/rel.h"
#include "utils/syscache.h"


static bool TargetListSupportsBackwardScan(List *targetlist);
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);
    }

    /* Shut down any SRFs in the plan node's targetlist */
    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_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_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_ValuesScanState:
            ExecReScanValuesScan((ValuesScanState *) node);
            break;

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

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

        case T_ForeignScanState:
            ExecReScanForeignScan((ForeignScanState *) 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.
 */
void
ExecMarkPos(PlanState *node)
{
    switch (nodeTag(node))
    {
        case T_SeqScanState:
            ExecSeqMarkPos((SeqScanState *) node);
            break;

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

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

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

        case T_ValuesScanState:
            ExecValuesMarkPos((ValuesScanState *) 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_SeqScanState:
            ExecSeqRestrPos((SeqScanState *) node);
            break;

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

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

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

        case T_ValuesScanState:
            ExecValuesRestrPos((ValuesScanState *) 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 plan type support mark/restore?
 *
 * XXX Ideally, all plan node types would support mark/restore, and this
 * wouldn't be needed.  For now, this had better match the routines above.
 * But note the test is on Plan nodetype, not PlanState nodetype.
 *
 * (However, since the only present use of mark/restore is in mergejoin,
 * there is no need to support mark/restore in any plan type that is not
 * capable of generating ordered output.  So the seqscan, tidscan,
 * and valuesscan support is actually useless code at present.)
 */
bool
ExecSupportsMarkRestore(NodeTag plantype)
{
    switch (plantype)
    {
        case T_SeqScan:
        case T_IndexScan:
        case T_IndexOnlyScan:
        case T_TidScan:
        case T_ValuesScan:
        case T_Material:
        case T_Sort:
            return true;

        case T_Result:

            /*
             * T_Result only supports mark/restore if it has a child plan that
             * does, so we do not have enough information to give a really
             * correct answer.  However, for current uses it's enough to
             * always say "false", because this routine is not asked about
             * gating Result plans, only base-case Results.
             */
            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;

    switch (nodeTag(node))
    {
        case T_Result:
            if (outerPlan(node) != NULL)
                return ExecSupportsBackwardScan(outerPlan(node)) &&
                    TargetListSupportsBackwardScan(node->targetlist);
            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_SeqScan:
        case T_TidScan:
        case T_FunctionScan:
        case T_ValuesScan:
        case T_CteScan:
            return TargetListSupportsBackwardScan(node->targetlist);

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

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

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

        case T_Material:
        case T_Sort:
            /* these don't evaluate tlist */
            return true;

        case T_LockRows:
        case T_Limit:
            /* these don't evaluate tlist */
            return ExecSupportsBackwardScan(outerPlan(node));

        default:
            return false;
    }
}

/*
 * If the tlist contains set-returning functions, we can't support backward
 * scan, because the TupFromTlist code is direction-ignorant.
 */
static bool
TargetListSupportsBackwardScan(List *targetlist)
{
    if (expression_returns_set((Node *) targetlist))
        return false;
    return true;
}

/*
 * 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;
    HeapTuple   ht_am;
    Form_pg_class idxrelrec;
    Form_pg_am  amrec;

    /* 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 pg_am tuple of the index' access method */
    ht_am = SearchSysCache1(AMOID, ObjectIdGetDatum(idxrelrec->relam));
    if (!HeapTupleIsValid(ht_am))
        elog(ERROR, "cache lookup failed for access method %u",
             idxrelrec->relam);
    amrec = (Form_pg_am) GETSTRUCT(ht_am);

    result = amrec->amcanbackward;

    ReleaseSysCache(ht_idxrel);
    ReleaseSysCache(ht_am);

    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_CteScan:
        case T_WorkTableScan:
        case T_Sort:
            return true;

        default:
            break;
    }

    return false;
}