385 lines
14 KiB
C++
385 lines
14 KiB
C++
/* -------------------------------------------------------------------------
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*
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* execScan.cpp
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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) 2020 Huawei Technologies Co.,Ltd.
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* Portions Copyright (c) 1996-2012, 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/gausskernel/runtime/executor/execScan.cpp
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*
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* -------------------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "knl/knl_variable.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 -- 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 TupleTableSlot* ExecScanFetch(ScanState* node, ExecScanAccessMtd access_mtd, ExecScanRecheckMtd recheck_mtd)
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{
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EState* estate = node->ps.state;
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if (estate->es_epqTuple != NULL) {
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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 scan_rel_id = ((Scan*)node->ps.plan)->scanrelid;
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Assert(scan_rel_id > 0);
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if (estate->es_epqTupleSet[scan_rel_id - 1]) {
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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[scan_rel_id - 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[scan_rel_id - 1] = true;
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/* Return empty slot if we haven't got a test tuple */
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if (estate->es_epqTuple[scan_rel_id - 1] == NULL)
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return ExecClearTuple(slot);
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/* Store test tuple in the plan node's scan slot */
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(void)ExecStoreTuple(estate->es_epqTuple[scan_rel_id - 1], slot, InvalidBuffer, false);
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/* Check if it meets the access-method conditions */
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if (!(*recheck_mtd)(node, slot))
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(void)ExecClearTuple(slot); /* would not be returned by 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 (*access_mtd)(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* ExecScan(ScanState* node, ExecScanAccessMtd access_mtd, /* function returning a tuple */
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ExecScanRecheckMtd recheck_mtd)
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{
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ExprContext* econtext = NULL;
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List* qual = NIL;
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ProjectionInfo* proj_info = NULL;
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ExprDoneCond is_done;
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TupleTableSlot* result_slot = NULL;
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if (node->isPartTbl && !PointerIsValid(node->partitions))
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return NULL;
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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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proj_info = node->ps.ps_ProjInfo;
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econtext = node->ps.ps_ExprContext;
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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 == NULL && proj_info == NULL) {
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ResetExprContext(econtext);
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return ExecScanFetch(node, access_mtd, recheck_mtd);
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}
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/*
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* Check to see if we're still projecting out tuples from a previous scan
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* tuple (because there is a function-returning-set in the projection
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* expressions). If so, try to project another one.
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*/
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if (node->ps.ps_TupFromTlist) {
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Assert(proj_info); /* can't get here if not projecting */
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result_slot = ExecProject(proj_info, &is_done);
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if (is_done == ExprMultipleResult)
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return result_slot;
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/* Done with that source tuple... */
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node->ps.ps_TupFromTlist = false;
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}
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/*
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* @hdfs
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* Optimize scan bu using informational constraint.
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* if the is_scan_false is true, the iteration is over.
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*/
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if (node->is_scan_end) {
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return NULL;
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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. Note this can't happen
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* until we're done projecting out tuples from a scan tuple.
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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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TupleTableSlot* slot = NULL;
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CHECK_FOR_INTERRUPTS();
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slot = ExecScanFetch(node, access_mtd, recheck_mtd);
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/* refresh qual every loop */
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qual = node->ps.qual;
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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) || unlikely(executorEarlyStop())) {
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if (proj_info != NULL)
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return ExecClearTuple(proj_info->pi_slot);
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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-nil qual here to avoid a function call to ExecQual()
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* when the qual is nil ... 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, false)) {
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/*
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* Found a satisfactory scan tuple.
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*/
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if (proj_info != NULL) {
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if (node->ps.state && node->ps.state->es_plannedstmt) {
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econtext->can_ignore = node->ps.state->es_plannedstmt->hasIgnore;
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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 --- unless we find we can project no tuples
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* from this scan tuple, in which case continue scan.
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*/
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result_slot = ExecProject(proj_info, &is_done);
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#ifdef PGXC
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/* Copy the xcnodeoid if underlying scanned slot has one */
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result_slot->tts_xcnodeoid = slot->tts_xcnodeoid;
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#endif /* PGXC */
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if (is_done != ExprEndResult) {
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node->ps.ps_TupFromTlist = (is_done == ExprMultipleResult);
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/*
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* @hdfs
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* Optimize foreign scan by using informational constraint.
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*/
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if (IsA(node->ps.plan, ForeignScan)) {
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ForeignScan* foreign_scan = (ForeignScan*)(node->ps.plan);
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if (foreign_scan->scan.scan_qual_optimized) {
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/*
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* If we find a suitable tuple, set is_scan_end value is true.
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* It means that we do not find suitable tuple in the next iteration,
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* the iteration is over.
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*/
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node->is_scan_end = true;
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}
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}
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return result_slot;
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}
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} else {
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/*
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* Optimize foreign scan by using informational constraint.
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*/
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if (IsA(node->ps.plan, ForeignScan)) {
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ForeignScan* foreign_scan = (ForeignScan*)(node->ps.plan);
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if (foreign_scan->scan.scan_qual_optimized) {
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/*
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* If we find a suitable tuple, set is_scan_end value is true.
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* It means that we do not find suitable tuple in the next iteration,
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* the iteration is over.
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*/
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node->is_scan_end = true;
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}
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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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} 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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* ExecAssignScanType must have been called already.
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*/
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void ExecAssignScanProjectionInfo(ScanState* node)
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{
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Scan* scan = (Scan*)node->ps.plan;
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Index var_no;
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/* Vars in an index-only scan's tlist should be INDEX_VAR */
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if (IsA(scan, IndexOnlyScan))
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var_no = INDEX_VAR;
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else
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var_no = scan->scanrelid;
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if (tlist_matches_tupdesc(&node->ps, scan->plan.targetlist, var_no, node->ss_ScanTupleSlot->tts_tupleDescriptor))
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node->ps.ps_ProjInfo = NULL;
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else
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ExecAssignProjectionInfo(&node->ps, node->ss_ScanTupleSlot->tts_tupleDescriptor);
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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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* This function is called by ExecInitExtensiblePlan to initialize projection info.
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* Usually the caller provides a targetlist describing the scan tuples, so we can
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* avoid a projection step by setting ps_ProjInfo to NULL. Such as "SELECT * FROM ...".
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*/
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void ExecAssignScanProjectionInfoWithVarno(ScanState* node, Index var_no)
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{
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Scan* scan = (Scan*)node->ps.plan;
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if (tlist_matches_tupdesc(&node->ps, scan->plan.targetlist, var_no, node->ss_ScanTupleSlot->tts_tupleDescriptor))
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node->ps.ps_ProjInfo = NULL;
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else
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ExecAssignProjectionInfo(&node->ps, node->ss_ScanTupleSlot->tts_tupleDescriptor);
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}
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bool tlist_matches_tupdesc(PlanState* ps, List* tlist, Index var_no, TupleDesc tup_desc)
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{
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int num_attrs = tup_desc->natts;
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int attr_no;
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bool has_oid = false;
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ListCell* tlist_item = list_head(tlist);
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/* Check the tlist attributes */
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for (attr_no = 1; attr_no <= num_attrs; attr_no++) {
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Form_pg_attribute att_tup = tup_desc->attrs[attr_no - 1];
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Var* var = NULL;
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if (tlist_item == NULL)
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return false; /* tlist too short */
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var = (Var*)((TargetEntry*)lfirst(tlist_item))->expr;
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if (var == NULL || !IsA(var, Var))
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return false; /* tlist item not a Var */
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/* if these Asserts fail, planner messed up */
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Assert(var->varno == var_no);
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Assert(var->varlevelsup == 0);
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if (var->varattno != attr_no)
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return false; /* out of order */
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if (att_tup->attisdropped)
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return false; /* table contains dropped columns */
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/*
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* Note: usually the Var's type should match the tupdesc exactly, but
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* in situations involving unions of columns that have different
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* typmods, the Var may have come from above the union and hence have
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* typmod -1. This is a legitimate situation since the Var still
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* describes the column, just not as exactly as the tupdesc does. We
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* could change the planner to prevent it, but it'd then insert
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* projection steps just to convert from specific typmod to typmod -1,
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* which is pretty silly.
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*/
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if (var->vartype != att_tup->atttypid || (var->vartypmod != att_tup->atttypmod && var->vartypmod != -1))
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return false; /* type mismatch */
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tlist_item = lnext(tlist_item);
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}
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if (tlist_item != NULL)
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return false; /* tlist too long */
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/*
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* If the plan context requires a particular hasoid setting, then that has
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* to match, too.
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*/
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if (ExecContextForcesOids(ps, &has_oid) && has_oid != tup_desc->tdhasoid)
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return false;
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return true;
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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 ExecScanReScan(ScanState* node)
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{
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EState* estate = node->ps.state;
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/* Stop projecting any tuples from SRFs in the targetlist */
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node->ps.ps_TupFromTlist = false;
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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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Index scan_rel_id = ((Scan*)node->ps.plan)->scanrelid;
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Assert(scan_rel_id > 0);
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estate->es_epqScanDone[scan_rel_id - 1] = false;
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}
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}
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