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-rw-r--r--src/backend/executor/execScan.c342
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+/*-------------------------------------------------------------------------
+ *
+ * execScan.c
+ * This code provides support for generalized relation scans. ExecScan
+ * is passed a node and a pointer to a function to "do the right thing"
+ * and return a tuple from the relation. ExecScan then does the tedious
+ * stuff - checking the qualification and projecting the tuple
+ * appropriately.
+ *
+ * Portions Copyright (c) 1996-2021, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ *
+ * IDENTIFICATION
+ * src/backend/executor/execScan.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "executor/executor.h"
+#include "miscadmin.h"
+#include "utils/memutils.h"
+
+
+
+/*
+ * ExecScanFetch -- check interrupts & fetch next potential tuple
+ *
+ * This routine is concerned with substituting a test tuple if we are
+ * inside an EvalPlanQual recheck. If we aren't, just execute
+ * the access method's next-tuple routine.
+ */
+static inline TupleTableSlot *
+ExecScanFetch(ScanState *node,
+ ExecScanAccessMtd accessMtd,
+ ExecScanRecheckMtd recheckMtd)
+{
+ EState *estate = node->ps.state;
+
+ CHECK_FOR_INTERRUPTS();
+
+ if (estate->es_epq_active != NULL)
+ {
+ EPQState *epqstate = estate->es_epq_active;
+
+ /*
+ * We are inside an EvalPlanQual recheck. Return the test tuple if
+ * one is available, after rechecking any access-method-specific
+ * conditions.
+ */
+ Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
+
+ if (scanrelid == 0)
+ {
+ /*
+ * This is a ForeignScan or CustomScan which has pushed down a
+ * join to the remote side. The recheck method is responsible not
+ * only for rechecking the scan/join quals but also for storing
+ * the correct tuple in the slot.
+ */
+
+ TupleTableSlot *slot = node->ss_ScanTupleSlot;
+
+ if (!(*recheckMtd) (node, slot))
+ ExecClearTuple(slot); /* would not be returned by scan */
+ return slot;
+ }
+ else if (epqstate->relsubs_done[scanrelid - 1])
+ {
+ /*
+ * Return empty slot, as we already performed an EPQ substitution
+ * for this relation.
+ */
+
+ TupleTableSlot *slot = node->ss_ScanTupleSlot;
+
+ /* Return empty slot, as we already returned a tuple */
+ return ExecClearTuple(slot);
+ }
+ else if (epqstate->relsubs_slot[scanrelid - 1] != NULL)
+ {
+ /*
+ * Return replacement tuple provided by the EPQ caller.
+ */
+
+ TupleTableSlot *slot = epqstate->relsubs_slot[scanrelid - 1];
+
+ Assert(epqstate->relsubs_rowmark[scanrelid - 1] == NULL);
+
+ /* Mark to remember that we shouldn't return more */
+ epqstate->relsubs_done[scanrelid - 1] = true;
+
+ /* Return empty slot if we haven't got a test tuple */
+ if (TupIsNull(slot))
+ return NULL;
+
+ /* Check if it meets the access-method conditions */
+ if (!(*recheckMtd) (node, slot))
+ return ExecClearTuple(slot); /* would not be returned by
+ * scan */
+ return slot;
+ }
+ else if (epqstate->relsubs_rowmark[scanrelid - 1] != NULL)
+ {
+ /*
+ * Fetch and return replacement tuple using a non-locking rowmark.
+ */
+
+ TupleTableSlot *slot = node->ss_ScanTupleSlot;
+
+ /* Mark to remember that we shouldn't return more */
+ epqstate->relsubs_done[scanrelid - 1] = true;
+
+ if (!EvalPlanQualFetchRowMark(epqstate, scanrelid, slot))
+ return NULL;
+
+ /* Return empty slot if we haven't got a test tuple */
+ if (TupIsNull(slot))
+ return NULL;
+
+ /* Check if it meets the access-method conditions */
+ if (!(*recheckMtd) (node, slot))
+ return ExecClearTuple(slot); /* would not be returned by
+ * scan */
+ return slot;
+ }
+ }
+
+ /*
+ * Run the node-type-specific access method function to get the next tuple
+ */
+ return (*accessMtd) (node);
+}
+
+/* ----------------------------------------------------------------
+ * ExecScan
+ *
+ * Scans the relation using the 'access method' indicated and
+ * returns the next qualifying tuple.
+ * The access method returns the next tuple and ExecScan() is
+ * responsible for checking the tuple returned against the qual-clause.
+ *
+ * A 'recheck method' must also be provided that can check an
+ * arbitrary tuple of the relation against any qual conditions
+ * that are implemented internal to the access method.
+ *
+ * Conditions:
+ * -- the "cursor" maintained by the AMI is positioned at the tuple
+ * returned previously.
+ *
+ * Initial States:
+ * -- the relation indicated is opened for scanning so that the
+ * "cursor" is positioned before the first qualifying tuple.
+ * ----------------------------------------------------------------
+ */
+TupleTableSlot *
+ExecScan(ScanState *node,
+ ExecScanAccessMtd accessMtd, /* function returning a tuple */
+ ExecScanRecheckMtd recheckMtd)
+{
+ ExprContext *econtext;
+ ExprState *qual;
+ ProjectionInfo *projInfo;
+
+ /*
+ * Fetch data from node
+ */
+ qual = node->ps.qual;
+ projInfo = node->ps.ps_ProjInfo;
+ econtext = node->ps.ps_ExprContext;
+
+ /* interrupt checks are in ExecScanFetch */
+
+ /*
+ * If we have neither a qual to check nor a projection to do, just skip
+ * all the overhead and return the raw scan tuple.
+ */
+ if (!qual && !projInfo)
+ {
+ ResetExprContext(econtext);
+ return ExecScanFetch(node, accessMtd, recheckMtd);
+ }
+
+ /*
+ * Reset per-tuple memory context to free any expression evaluation
+ * storage allocated in the previous tuple cycle.
+ */
+ ResetExprContext(econtext);
+
+ /*
+ * get a tuple from the access method. Loop until we obtain a tuple that
+ * passes the qualification.
+ */
+ for (;;)
+ {
+ TupleTableSlot *slot;
+
+ slot = ExecScanFetch(node, accessMtd, recheckMtd);
+
+ /*
+ * if the slot returned by the accessMtd contains NULL, then it means
+ * there is nothing more to scan so we just return an empty slot,
+ * being careful to use the projection result slot so it has correct
+ * tupleDesc.
+ */
+ if (TupIsNull(slot))
+ {
+ if (projInfo)
+ return ExecClearTuple(projInfo->pi_state.resultslot);
+ else
+ return slot;
+ }
+
+ /*
+ * place the current tuple into the expr context
+ */
+ econtext->ecxt_scantuple = slot;
+
+ /*
+ * check that the current tuple satisfies the qual-clause
+ *
+ * check for non-null qual here to avoid a function call to ExecQual()
+ * when the qual is null ... saves only a few cycles, but they add up
+ * ...
+ */
+ if (qual == NULL || ExecQual(qual, econtext))
+ {
+ /*
+ * Found a satisfactory scan tuple.
+ */
+ if (projInfo)
+ {
+ /*
+ * Form a projection tuple, store it in the result tuple slot
+ * and return it.
+ */
+ return ExecProject(projInfo);
+ }
+ else
+ {
+ /*
+ * Here, we aren't projecting, so just return scan tuple.
+ */
+ return slot;
+ }
+ }
+ else
+ InstrCountFiltered1(node, 1);
+
+ /*
+ * Tuple fails qual, so free per-tuple memory and try again.
+ */
+ ResetExprContext(econtext);
+ }
+}
+
+/*
+ * ExecAssignScanProjectionInfo
+ * Set up projection info for a scan node, if necessary.
+ *
+ * We can avoid a projection step if the requested tlist exactly matches
+ * the underlying tuple type. If so, we just set ps_ProjInfo to NULL.
+ * Note that this case occurs not only for simple "SELECT * FROM ...", but
+ * also in most cases where there are joins or other processing nodes above
+ * the scan node, because the planner will preferentially generate a matching
+ * tlist.
+ *
+ * The scan slot's descriptor must have been set already.
+ */
+void
+ExecAssignScanProjectionInfo(ScanState *node)
+{
+ Scan *scan = (Scan *) node->ps.plan;
+ TupleDesc tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
+
+ ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, scan->scanrelid);
+}
+
+/*
+ * ExecAssignScanProjectionInfoWithVarno
+ * As above, but caller can specify varno expected in Vars in the tlist.
+ */
+void
+ExecAssignScanProjectionInfoWithVarno(ScanState *node, Index varno)
+{
+ TupleDesc tupdesc = node->ss_ScanTupleSlot->tts_tupleDescriptor;
+
+ ExecConditionalAssignProjectionInfo(&node->ps, tupdesc, varno);
+}
+
+/*
+ * ExecScanReScan
+ *
+ * This must be called within the ReScan function of any plan node type
+ * that uses ExecScan().
+ */
+void
+ExecScanReScan(ScanState *node)
+{
+ EState *estate = node->ps.state;
+
+ /*
+ * We must clear the scan tuple so that observers (e.g., execCurrent.c)
+ * can tell that this plan node is not positioned on a tuple.
+ */
+ ExecClearTuple(node->ss_ScanTupleSlot);
+
+ /* Rescan EvalPlanQual tuple if we're inside an EvalPlanQual recheck */
+ if (estate->es_epq_active != NULL)
+ {
+ EPQState *epqstate = estate->es_epq_active;
+ Index scanrelid = ((Scan *) node->ps.plan)->scanrelid;
+
+ if (scanrelid > 0)
+ epqstate->relsubs_done[scanrelid - 1] = false;
+ else
+ {
+ Bitmapset *relids;
+ int rtindex = -1;
+
+ /*
+ * If an FDW or custom scan provider has replaced the join with a
+ * scan, there are multiple RTIs; reset the epqScanDone flag for
+ * all of them.
+ */
+ if (IsA(node->ps.plan, ForeignScan))
+ relids = ((ForeignScan *) node->ps.plan)->fs_relids;
+ else if (IsA(node->ps.plan, CustomScan))
+ relids = ((CustomScan *) node->ps.plan)->custom_relids;
+ else
+ elog(ERROR, "unexpected scan node: %d",
+ (int) nodeTag(node->ps.plan));
+
+ while ((rtindex = bms_next_member(relids, rtindex)) >= 0)
+ {
+ Assert(rtindex > 0);
+ epqstate->relsubs_done[rtindex - 1] = false;
+ }
+ }
+ }
+}
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