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37fa3b6c89
the next are handled by ReleaseAndReadBuffer rather than separate ReleaseBuffer and ReadBuffer calls. This cuts the number of acquisitions of the BufMgrLock by a factor of 2 (possibly more, if an indexscan happens to pull successive rows from the same heap page). Unfortunately this doesn't seem enough to get us out of the recently discussed context-switch storm problem, but it's surely worth doing anyway.
472 lines
12 KiB
C
472 lines
12 KiB
C
/*-------------------------------------------------------------------------
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*
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* nodeTidscan.c
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* Routines to support direct tid scans of relations
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*
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* Portions Copyright (c) 1996-2003, 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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* $PostgreSQL: pgsql/src/backend/executor/nodeTidscan.c,v 1.37 2004/04/21 18:24:26 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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/*
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* INTERFACE ROUTINES
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*
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* ExecTidScan scans a relation using tids
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* ExecInitTidScan creates and initializes state info.
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* ExecTidReScan rescans the tid relation.
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* ExecEndTidScan releases all storage.
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* ExecTidMarkPos marks scan position.
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* ExecTidRestrPos restores scan position.
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*/
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#include "postgres.h"
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#include "executor/execdebug.h"
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#include "executor/nodeTidscan.h"
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#include "access/heapam.h"
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#include "parser/parsetree.h"
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static void TidListCreate(TidScanState *tidstate);
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static TupleTableSlot *TidNext(TidScanState *node);
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/*
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* Compute the list of TIDs to be visited, by evaluating the expressions
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* for them.
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*/
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static void
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TidListCreate(TidScanState *tidstate)
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{
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List *evalList = tidstate->tss_tideval;
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ExprContext *econtext = tidstate->ss.ps.ps_ExprContext;
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ItemPointerData *tidList;
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int numTids = 0;
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List *lst;
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tidList = (ItemPointerData *)
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palloc(length(tidstate->tss_tideval) * sizeof(ItemPointerData));
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foreach(lst, evalList)
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{
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ItemPointer itemptr;
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bool isNull;
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itemptr = (ItemPointer)
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DatumGetPointer(ExecEvalExprSwitchContext(lfirst(lst),
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econtext,
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&isNull,
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NULL));
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if (!isNull && itemptr && ItemPointerIsValid(itemptr))
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{
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tidList[numTids] = *itemptr;
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numTids++;
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}
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}
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tidstate->tss_TidList = tidList;
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tidstate->tss_NumTids = numTids;
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tidstate->tss_TidPtr = -1;
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}
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/* ----------------------------------------------------------------
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* TidNext
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*
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* Retrieve a tuple from the TidScan node's currentRelation
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* using the tids in the TidScanState information.
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*
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* ----------------------------------------------------------------
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*/
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static TupleTableSlot *
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TidNext(TidScanState *node)
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{
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EState *estate;
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ScanDirection direction;
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Snapshot snapshot;
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Relation heapRelation;
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HeapTuple tuple;
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TupleTableSlot *slot;
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Index scanrelid;
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Buffer buffer = InvalidBuffer;
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ItemPointerData *tidList;
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int numTids;
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bool bBackward;
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int tidNumber;
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/*
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* extract necessary information from tid scan node
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*/
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estate = node->ss.ps.state;
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direction = estate->es_direction;
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snapshot = estate->es_snapshot;
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heapRelation = node->ss.ss_currentRelation;
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slot = node->ss.ss_ScanTupleSlot;
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scanrelid = ((TidScan *) node->ss.ps.plan)->scan.scanrelid;
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/*
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* Clear any reference to the previously returned tuple. This doesn't
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* offer any great performance benefit, but it keeps this code in sync
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* with SeqNext and IndexNext.
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*/
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ExecClearTuple(slot);
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/*
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* Check if we are evaluating PlanQual for tuple of this relation.
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* Additional checking is not good, but no other way for now. We could
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* introduce new nodes for this case and handle TidScan --> NewNode
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* switching in Init/ReScan plan...
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*/
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if (estate->es_evTuple != NULL &&
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estate->es_evTuple[scanrelid - 1] != NULL)
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{
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if (estate->es_evTupleNull[scanrelid - 1])
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return slot; /* return empty slot */
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/*
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* XXX shouldn't we check here to make sure tuple matches TID
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* list? In runtime-key case this is not certain, is it?
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*/
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ExecStoreTuple(estate->es_evTuple[scanrelid - 1],
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slot, InvalidBuffer, false);
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/* Flag for the next call that no more tuples */
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estate->es_evTupleNull[scanrelid - 1] = true;
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return (slot);
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}
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/*
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* First time through, compute the list of TIDs to be visited
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*/
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if (node->tss_TidList == NULL)
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TidListCreate(node);
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tidList = node->tss_TidList;
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numTids = node->tss_NumTids;
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tuple = &(node->tss_htup);
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/*
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* ok, now that we have what we need, fetch an tid tuple. if scanning
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* this tid succeeded then return the appropriate heap tuple.. else
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* return NULL.
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*/
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bBackward = ScanDirectionIsBackward(direction);
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if (bBackward)
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{
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tidNumber = numTids - node->tss_TidPtr - 1;
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if (tidNumber < 0)
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{
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tidNumber = 0;
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node->tss_TidPtr = numTids - 1;
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}
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}
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else
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{
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if ((tidNumber = node->tss_TidPtr) < 0)
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{
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tidNumber = 0;
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node->tss_TidPtr = 0;
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}
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}
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while (tidNumber < numTids)
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{
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bool slot_is_valid = false;
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tuple->t_self = tidList[node->tss_TidPtr];
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if (heap_fetch(heapRelation, snapshot, tuple, &buffer, false, NULL))
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{
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bool prev_matches = false;
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int prev_tid;
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/*
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* store the scanned tuple in the scan tuple slot of the scan
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* state. Eventually we will only do this and not return a
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* tuple. Note: we pass 'false' because tuples returned by
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* amgetnext are pointers onto disk pages and were not created
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* with palloc() and so should not be pfree()'d.
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*/
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ExecStoreTuple(tuple, /* tuple to store */
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slot, /* slot to store in */
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buffer, /* buffer associated with tuple */
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false); /* don't pfree */
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/*
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* At this point we have an extra pin on the buffer, because
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* ExecStoreTuple incremented the pin count. Drop our local
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* pin.
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*/
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ReleaseBuffer(buffer);
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/*
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* We must check to see if the current tuple would have been
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* matched by an earlier tid, so we don't double report it.
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*/
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for (prev_tid = 0; prev_tid < node->tss_TidPtr;
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prev_tid++)
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{
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if (ItemPointerEquals(&tidList[prev_tid], &tuple->t_self))
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{
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prev_matches = true;
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break;
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}
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}
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if (!prev_matches)
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slot_is_valid = true;
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else
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ExecClearTuple(slot);
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}
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tidNumber++;
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if (bBackward)
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node->tss_TidPtr--;
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else
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node->tss_TidPtr++;
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if (slot_is_valid)
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return slot;
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}
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/*
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* if we get here it means the tid scan failed so we are at the end of
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* the scan..
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*/
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return ExecClearTuple(slot);
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}
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/* ----------------------------------------------------------------
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* ExecTidScan(node)
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*
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* Scans the relation using tids and returns
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* the next qualifying tuple in the direction specified.
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* It calls ExecScan() and passes it the access methods which returns
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* the next tuple using the tids.
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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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* -- tidPtr points to the first tid.
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* -- state variable ruleFlag = nil.
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* ----------------------------------------------------------------
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*/
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TupleTableSlot *
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ExecTidScan(TidScanState *node)
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{
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/*
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* use TidNext as access method
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*/
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return ExecScan(&node->ss, (ExecScanAccessMtd) TidNext);
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}
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/* ----------------------------------------------------------------
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* ExecTidReScan(node)
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* ----------------------------------------------------------------
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*/
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void
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ExecTidReScan(TidScanState *node, ExprContext *exprCtxt)
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{
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EState *estate;
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Index scanrelid;
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estate = node->ss.ps.state;
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scanrelid = ((TidScan *) node->ss.ps.plan)->scan.scanrelid;
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/* If we are being passed an outer tuple, save it for runtime key calc */
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if (exprCtxt != NULL)
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node->ss.ps.ps_ExprContext->ecxt_outertuple =
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exprCtxt->ecxt_outertuple;
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/* If this is re-scanning of PlanQual ... */
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if (estate->es_evTuple != NULL &&
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estate->es_evTuple[scanrelid - 1] != NULL)
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{
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estate->es_evTupleNull[scanrelid - 1] = false;
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return;
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}
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if (node->tss_TidList)
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pfree(node->tss_TidList);
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node->tss_TidList = NULL;
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node->tss_NumTids = 0;
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node->tss_TidPtr = -1;
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}
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/* ----------------------------------------------------------------
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* ExecEndTidScan
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*
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* Releases any storage allocated through C routines.
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* Returns nothing.
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* ----------------------------------------------------------------
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*/
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void
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ExecEndTidScan(TidScanState *node)
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{
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/*
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* Free the exprcontext
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*/
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ExecFreeExprContext(&node->ss.ps);
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/*
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* clear out tuple table slots
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*/
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ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);
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ExecClearTuple(node->ss.ss_ScanTupleSlot);
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/*
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* close the heap relation.
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*
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* Currently, we do not release the AccessShareLock acquired by
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* ExecInitTidScan. This lock should be held till end of transaction.
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* (There is a faction that considers this too much locking, however.)
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*/
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heap_close(node->ss.ss_currentRelation, NoLock);
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}
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/* ----------------------------------------------------------------
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* ExecTidMarkPos
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*
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* Marks scan position by marking the current tid.
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* Returns nothing.
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* ----------------------------------------------------------------
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*/
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void
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ExecTidMarkPos(TidScanState *node)
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{
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node->tss_MarkTidPtr = node->tss_TidPtr;
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}
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/* ----------------------------------------------------------------
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* ExecTidRestrPos
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*
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* Restores scan position by restoring the current tid.
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* Returns nothing.
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*
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* XXX Assumes previously marked scan position belongs to current tid
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* ----------------------------------------------------------------
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*/
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void
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ExecTidRestrPos(TidScanState *node)
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{
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node->tss_TidPtr = node->tss_MarkTidPtr;
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}
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/* ----------------------------------------------------------------
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* ExecInitTidScan
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*
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* Initializes the tid scan's state information, creates
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* scan keys, and opens the base and tid relations.
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*
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* Parameters:
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* node: TidNode node produced by the planner.
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* estate: the execution state initialized in InitPlan.
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* ----------------------------------------------------------------
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*/
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TidScanState *
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ExecInitTidScan(TidScan *node, EState *estate)
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{
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TidScanState *tidstate;
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List *rangeTable;
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RangeTblEntry *rtentry;
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Oid relid;
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Oid reloid;
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Relation currentRelation;
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Bitmapset *execParam = NULL;
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/*
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* create state structure
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*/
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tidstate = makeNode(TidScanState);
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tidstate->ss.ps.plan = (Plan *) node;
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tidstate->ss.ps.state = estate;
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/*
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* Miscellaneous initialization
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*
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* create expression context for node
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*/
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ExecAssignExprContext(estate, &tidstate->ss.ps);
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/*
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* initialize child expressions
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*/
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tidstate->ss.ps.targetlist = (List *)
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ExecInitExpr((Expr *) node->scan.plan.targetlist,
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(PlanState *) tidstate);
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tidstate->ss.ps.qual = (List *)
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ExecInitExpr((Expr *) node->scan.plan.qual,
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(PlanState *) tidstate);
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tidstate->tss_tideval = (List *)
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ExecInitExpr((Expr *) node->tideval,
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(PlanState *) tidstate);
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#define TIDSCAN_NSLOTS 2
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/*
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* tuple table initialization
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*/
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ExecInitResultTupleSlot(estate, &tidstate->ss.ps);
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ExecInitScanTupleSlot(estate, &tidstate->ss);
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/*
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* mark tid list as not computed yet
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*/
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tidstate->tss_TidList = NULL;
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tidstate->tss_NumTids = 0;
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tidstate->tss_TidPtr = -1;
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/*
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* get the range table and direction information from the execution
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* state (these are needed to open the relations).
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*/
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rangeTable = estate->es_range_table;
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/*
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* open the base relation
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*
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* We acquire AccessShareLock for the duration of the scan.
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*/
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relid = node->scan.scanrelid;
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rtentry = rt_fetch(relid, rangeTable);
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reloid = rtentry->relid;
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currentRelation = heap_open(reloid, AccessShareLock);
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tidstate->ss.ss_currentRelation = currentRelation;
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tidstate->ss.ss_currentScanDesc = NULL; /* no heap scan here */
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/*
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* get the scan type from the relation descriptor.
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*/
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ExecAssignScanType(&tidstate->ss, RelationGetDescr(currentRelation), false);
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/*
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* if there are some PARAM_EXEC in skankeys then force tid rescan on
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* first scan.
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*/
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tidstate->ss.ps.chgParam = execParam;
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/*
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* Initialize result tuple type and projection info.
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*/
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ExecAssignResultTypeFromTL(&tidstate->ss.ps);
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ExecAssignScanProjectionInfo(&tidstate->ss);
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/*
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* all done.
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*/
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return tidstate;
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}
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int
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ExecCountSlotsTidScan(TidScan *node)
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{
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return ExecCountSlotsNode(outerPlan((Plan *) node)) +
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ExecCountSlotsNode(innerPlan((Plan *) node)) + TIDSCAN_NSLOTS;
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}
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