304 lines
8.2 KiB
C
304 lines
8.2 KiB
C
/*-------------------------------------------------------------------------
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*
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* execScan.c
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* This code provides support for generalized relation scans. ExecScan
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* is passed a node and a pointer to a function to "do the right thing"
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* and return a tuple from the relation. ExecScan then does the tedious
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* stuff - checking the qualification and projecting the tuple
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* appropriately.
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*
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* Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* src/backend/executor/execScan.c
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*
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*-------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "executor/executor.h"
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#include "miscadmin.h"
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#include "utils/memutils.h"
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/*
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* ExecScanFetch -- check interrupts & fetch next potential tuple
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*
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* This routine is concerned with substituting a test tuple if we are
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* inside an EvalPlanQual recheck. If we aren't, just execute
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* the access method's next-tuple routine.
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*/
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static inline TupleTableSlot *
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ExecScanFetch(ScanState *node,
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ExecScanAccessMtd accessMtd,
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ExecScanRecheckMtd recheckMtd)
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{
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EState *estate = node->ps.state;
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CHECK_FOR_INTERRUPTS();
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if (estate->es_epqTupleSlot != NULL)
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{
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/*
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* We are inside an EvalPlanQual recheck. Return the test tuple if
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* one is available, after rechecking any access-method-specific
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* conditions.
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*/
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Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
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if (scanrelid == 0)
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{
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TupleTableSlot *slot = node->ss_ScanTupleSlot;
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/*
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* This is a ForeignScan or CustomScan which has pushed down a
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* join to the remote side. The recheck method is responsible not
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* only for rechecking the scan/join quals but also for storing
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* the correct tuple in the slot.
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*/
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if (!(*recheckMtd) (node, slot))
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ExecClearTuple(slot); /* would not be returned by scan */
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return slot;
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}
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else if (estate->es_epqTupleSlot[scanrelid - 1] != NULL)
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{
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TupleTableSlot *slot = node->ss_ScanTupleSlot;
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/* Return empty slot if we already returned a tuple */
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if (estate->es_epqScanDone[scanrelid - 1])
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return ExecClearTuple(slot);
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/* Else mark to remember that we shouldn't return more */
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estate->es_epqScanDone[scanrelid - 1] = true;
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slot = estate->es_epqTupleSlot[scanrelid - 1];
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/* Return empty slot if we haven't got a test tuple */
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if (TupIsNull(slot))
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return NULL;
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/* Check if it meets the access-method conditions */
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if (!(*recheckMtd) (node, slot))
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return ExecClearTuple(slot); /* would not be returned by
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* scan */
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return slot;
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}
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}
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/*
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* Run the node-type-specific access method function to get the next tuple
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*/
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return (*accessMtd) (node);
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}
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/* ----------------------------------------------------------------
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* ExecScan
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*
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* Scans the relation using the 'access method' indicated and
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* returns the next qualifying tuple in the direction specified
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* in the global variable ExecDirection.
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* The access method returns the next tuple and ExecScan() is
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* responsible for checking the tuple returned against the qual-clause.
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*
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* A 'recheck method' must also be provided that can check an
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* arbitrary tuple of the relation against any qual conditions
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* that are implemented internal to the access method.
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*
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* Conditions:
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* -- the "cursor" maintained by the AMI is positioned at the tuple
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* returned previously.
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*
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* Initial States:
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* -- the relation indicated is opened for scanning so that the
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* "cursor" is positioned before the first qualifying tuple.
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* ----------------------------------------------------------------
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*/
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TupleTableSlot *
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ExecScan(ScanState *node,
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ExecScanAccessMtd accessMtd, /* function returning a tuple */
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ExecScanRecheckMtd recheckMtd)
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{
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ExprContext *econtext;
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ExprState *qual;
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ProjectionInfo *projInfo;
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/*
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* Fetch data from node
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*/
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qual = node->ps.qual;
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projInfo = node->ps.ps_ProjInfo;
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econtext = node->ps.ps_ExprContext;
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/* interrupt checks are in ExecScanFetch */
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/*
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* If we have neither a qual to check nor a projection to do, just skip
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* all the overhead and return the raw scan tuple.
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*/
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if (!qual && !projInfo)
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{
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ResetExprContext(econtext);
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return ExecScanFetch(node, accessMtd, recheckMtd);
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}
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/*
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* Reset per-tuple memory context to free any expression evaluation
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* storage allocated in the previous tuple cycle.
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*/
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ResetExprContext(econtext);
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/*
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* get a tuple from the access method. Loop until we obtain a tuple that
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* passes the qualification.
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*/
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for (;;)
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{
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TupleTableSlot *slot;
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slot = ExecScanFetch(node, accessMtd, recheckMtd);
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/*
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* if the slot returned by the accessMtd contains NULL, then it means
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* there is nothing more to scan so we just return an empty slot,
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* being careful to use the projection result slot so it has correct
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* tupleDesc.
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*/
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if (TupIsNull(slot))
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{
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if (projInfo)
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return ExecClearTuple(projInfo->pi_state.resultslot);
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else
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return slot;
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}
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/*
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* place the current tuple into the expr context
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*/
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econtext->ecxt_scantuple = slot;
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/*
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* check that the current tuple satisfies the qual-clause
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*
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* check for non-null qual here to avoid a function call to ExecQual()
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* when the qual is null ... saves only a few cycles, but they add up
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* ...
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*/
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if (qual == NULL || ExecQual(qual, econtext))
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{
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/*
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* Found a satisfactory scan tuple.
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*/
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if (projInfo)
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{
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/*
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* Form a projection tuple, store it in the result tuple slot
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* and return it.
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*/
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return ExecProject(projInfo);
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}
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else
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{
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/*
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* Here, we aren't projecting, so just return scan tuple.
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*/
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return slot;
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}
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}
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else
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InstrCountFiltered1(node, 1);
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/*
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* Tuple fails qual, so free per-tuple memory and try again.
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*/
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ResetExprContext(econtext);
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}
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}
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/*
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* ExecAssignScanProjectionInfo
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* Set up projection info for a scan node, if necessary.
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*
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* We can avoid a projection step if the requested tlist exactly matches
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* the underlying tuple type. If so, we just set ps_ProjInfo to NULL.
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* Note that this case occurs not only for simple "SELECT * FROM ...", but
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* also in most cases where there are joins or other processing nodes above
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* the scan node, because the planner will preferentially generate a matching
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* tlist.
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*
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* The scan slot's descriptor must have been set already.
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*/
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void
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ExecAssignScanProjectionInfo(ScanState *node)
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{
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Scan *scan = (Scan *) node->ps.plan;
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TupleDesc tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
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ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, scan->scanrelid);
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}
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/*
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* ExecAssignScanProjectionInfoWithVarno
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* As above, but caller can specify varno expected in Vars in the tlist.
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*/
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void
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ExecAssignScanProjectionInfoWithVarno(ScanState *node, Index varno)
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{
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TupleDesc tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
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ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, varno);
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}
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/*
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* ExecScanReScan
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*
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* This must be called within the ReScan function of any plan node type
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* that uses ExecScan().
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*/
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void
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ExecScanReScan(ScanState *node)
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{
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EState *estate = node->ps.state;
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/*
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* We must clear the scan tuple so that observers (e.g., execCurrent.c)
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* can tell that this plan node is not positioned on a tuple.
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*/
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ExecClearTuple(node->ss_ScanTupleSlot);
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/* Rescan EvalPlanQual tuple if we're inside an EvalPlanQual recheck */
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if (estate->es_epqScanDone != NULL)
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{
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Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
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if (scanrelid > 0)
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estate->es_epqScanDone[scanrelid - 1] = false;
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else
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{
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Bitmapset *relids;
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int rtindex = -1;
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/*
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* If an FDW or custom scan provider has replaced the join with a
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* scan, there are multiple RTIs; reset the epqScanDone flag for
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* all of them.
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*/
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if (IsA(node->ps.plan, ForeignScan))
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relids = ((ForeignScan *) node->ps.plan)->fs_relids;
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else if (IsA(node->ps.plan, CustomScan))
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relids = ((CustomScan *) node->ps.plan)->custom_relids;
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else
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elog(ERROR, "unexpected scan node: %d",
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(int) nodeTag(node->ps.plan));
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while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
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{
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Assert(rtindex > 0);
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estate->es_epqScanDone[rtindex - 1] = false;
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}
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}
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}
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}
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