560 lines
14 KiB
C
560 lines
14 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) 1996-2010, 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 1.65 2010/01/02 16:57:45 momjian 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 "access/heapam.h"
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#include "access/sysattr.h"
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#include "catalog/pg_type.h"
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#include "executor/execdebug.h"
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#include "executor/nodeTidscan.h"
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#include "optimizer/clauses.h"
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#include "storage/bufmgr.h"
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#include "utils/array.h"
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#define IsCTIDVar(node) \
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((node) != NULL && \
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IsA((node), Var) && \
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((Var *) (node))->varattno == SelfItemPointerAttributeNumber && \
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((Var *) (node))->varlevelsup == 0)
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static void TidListCreate(TidScanState *tidstate);
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static int itemptr_comparator(const void *a, const void *b);
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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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* (The result is actually an array, not a list.)
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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_tidquals;
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ExprContext *econtext = tidstate->ss.ps.ps_ExprContext;
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BlockNumber nblocks;
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ItemPointerData *tidList;
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int numAllocTids;
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int numTids;
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ListCell *l;
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/*
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* We silently discard any TIDs that are out of range at the time of scan
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* start. (Since we hold at least AccessShareLock on the table, it won't
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* be possible for someone to truncate away the blocks we intend to
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* visit.)
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*/
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nblocks = RelationGetNumberOfBlocks(tidstate->ss.ss_currentRelation);
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/*
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* We initialize the array with enough slots for the case that all quals
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* are simple OpExprs or CurrentOfExprs. If there are any
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* ScalarArrayOpExprs, we may have to enlarge the array.
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*/
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numAllocTids = list_length(evalList);
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tidList = (ItemPointerData *)
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palloc(numAllocTids * sizeof(ItemPointerData));
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numTids = 0;
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tidstate->tss_isCurrentOf = false;
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foreach(l, evalList)
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{
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ExprState *exstate = (ExprState *) lfirst(l);
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Expr *expr = exstate->expr;
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ItemPointer itemptr;
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bool isNull;
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if (is_opclause(expr))
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{
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FuncExprState *fexstate = (FuncExprState *) exstate;
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Node *arg1;
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Node *arg2;
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arg1 = get_leftop(expr);
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arg2 = get_rightop(expr);
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if (IsCTIDVar(arg1))
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exstate = (ExprState *) lsecond(fexstate->args);
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else if (IsCTIDVar(arg2))
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exstate = (ExprState *) linitial(fexstate->args);
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else
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elog(ERROR, "could not identify CTID variable");
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itemptr = (ItemPointer)
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DatumGetPointer(ExecEvalExprSwitchContext(exstate,
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econtext,
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&isNull,
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NULL));
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if (!isNull &&
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ItemPointerIsValid(itemptr) &&
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ItemPointerGetBlockNumber(itemptr) < nblocks)
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{
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if (numTids >= numAllocTids)
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{
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numAllocTids *= 2;
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tidList = (ItemPointerData *)
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repalloc(tidList,
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numAllocTids * sizeof(ItemPointerData));
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}
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tidList[numTids++] = *itemptr;
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}
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}
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else if (expr && IsA(expr, ScalarArrayOpExpr))
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{
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ScalarArrayOpExprState *saexstate = (ScalarArrayOpExprState *) exstate;
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Datum arraydatum;
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ArrayType *itemarray;
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Datum *ipdatums;
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bool *ipnulls;
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int ndatums;
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int i;
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exstate = (ExprState *) lsecond(saexstate->fxprstate.args);
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arraydatum = ExecEvalExprSwitchContext(exstate,
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econtext,
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&isNull,
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NULL);
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if (isNull)
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continue;
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itemarray = DatumGetArrayTypeP(arraydatum);
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deconstruct_array(itemarray,
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TIDOID, SizeOfIptrData, false, 's',
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&ipdatums, &ipnulls, &ndatums);
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if (numTids + ndatums > numAllocTids)
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{
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numAllocTids = numTids + ndatums;
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tidList = (ItemPointerData *)
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repalloc(tidList,
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numAllocTids * sizeof(ItemPointerData));
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}
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for (i = 0; i < ndatums; i++)
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{
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if (!ipnulls[i])
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{
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itemptr = (ItemPointer) DatumGetPointer(ipdatums[i]);
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if (ItemPointerIsValid(itemptr) &&
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ItemPointerGetBlockNumber(itemptr) < nblocks)
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tidList[numTids++] = *itemptr;
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}
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}
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pfree(ipdatums);
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pfree(ipnulls);
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}
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else if (expr && IsA(expr, CurrentOfExpr))
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{
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CurrentOfExpr *cexpr = (CurrentOfExpr *) expr;
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ItemPointerData cursor_tid;
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if (execCurrentOf(cexpr, econtext,
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RelationGetRelid(tidstate->ss.ss_currentRelation),
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&cursor_tid))
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{
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if (numTids >= numAllocTids)
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{
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numAllocTids *= 2;
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tidList = (ItemPointerData *)
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repalloc(tidList,
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numAllocTids * sizeof(ItemPointerData));
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}
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tidList[numTids++] = cursor_tid;
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tidstate->tss_isCurrentOf = true;
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}
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}
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else
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elog(ERROR, "could not identify CTID expression");
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}
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/*
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* Sort the array of TIDs into order, and eliminate duplicates.
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* Eliminating duplicates is necessary since we want OR semantics across
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* the list. Sorting makes it easier to detect duplicates, and as a bonus
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* ensures that we will visit the heap in the most efficient way.
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*/
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if (numTids > 1)
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{
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int lastTid;
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int i;
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/* CurrentOfExpr could never appear OR'd with something else */
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Assert(!tidstate->tss_isCurrentOf);
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qsort((void *) tidList, numTids, sizeof(ItemPointerData),
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itemptr_comparator);
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lastTid = 0;
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for (i = 1; i < numTids; i++)
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{
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if (!ItemPointerEquals(&tidList[lastTid], &tidList[i]))
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tidList[++lastTid] = tidList[i];
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}
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numTids = lastTid + 1;
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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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* qsort comparator for ItemPointerData items
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*/
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static int
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itemptr_comparator(const void *a, const void *b)
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{
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const ItemPointerData *ipa = (const ItemPointerData *) a;
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const ItemPointerData *ipb = (const ItemPointerData *) b;
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BlockNumber ba = ItemPointerGetBlockNumber(ipa);
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BlockNumber bb = ItemPointerGetBlockNumber(ipb);
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OffsetNumber oa = ItemPointerGetOffsetNumber(ipa);
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OffsetNumber ob = ItemPointerGetOffsetNumber(ipb);
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if (ba < bb)
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return -1;
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if (ba > bb)
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return 1;
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if (oa < ob)
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return -1;
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if (oa > ob)
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return 1;
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return 0;
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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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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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/*
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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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/*
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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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* Initialize or advance scan position, depending on direction.
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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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if (node->tss_TidPtr < 0)
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{
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/* initialize for backward scan */
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node->tss_TidPtr = numTids - 1;
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}
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else
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node->tss_TidPtr--;
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}
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else
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{
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if (node->tss_TidPtr < 0)
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{
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/* initialize for forward scan */
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node->tss_TidPtr = 0;
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}
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else
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node->tss_TidPtr++;
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}
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while (node->tss_TidPtr >= 0 && node->tss_TidPtr < numTids)
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{
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tuple->t_self = tidList[node->tss_TidPtr];
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/*
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* For WHERE CURRENT OF, the tuple retrieved from the cursor might
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* since have been updated; if so, we should fetch the version that is
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* current according to our snapshot.
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*/
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if (node->tss_isCurrentOf)
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heap_get_latest_tid(heapRelation, snapshot, &tuple->t_self);
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if (heap_fetch(heapRelation, snapshot, tuple, &buffer, false, NULL))
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{
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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 tuple.
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* Note: we pass 'false' because tuples returned by amgetnext are
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* pointers onto disk pages and were not created with palloc() and
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* 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 pin.
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*/
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ReleaseBuffer(buffer);
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return slot;
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}
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/* Bad TID or failed snapshot qual; try next */
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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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}
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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 the
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* scan..
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*/
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return ExecClearTuple(slot);
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}
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/*
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* TidRecheck -- access method routine to recheck a tuple in EvalPlanQual
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*/
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static bool
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TidRecheck(TidScanState *node, TupleTableSlot *slot)
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{
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/*
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* XXX shouldn't we check here to make sure tuple matches TID list? In
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* runtime-key case this is not certain, is it? However, in the WHERE
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* CURRENT OF case it might not match anyway ...
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*/
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return true;
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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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* We call the ExecScan() routine and pass it the appropriate
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* access method functions.
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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 is -1.
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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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return ExecScan(&node->ss,
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(ExecScanAccessMtd) TidNext,
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(ExecScanRecheckMtd) TidRecheck);
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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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/* 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 (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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ExecScanReScan(&node->ss);
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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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ExecCloseScanRelation(node->ss.ss_currentRelation);
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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, int eflags)
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{
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TidScanState *tidstate;
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Relation currentRelation;
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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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tidstate->ss.ps.ps_TupFromTlist = false;
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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_tidquals = (List *)
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ExecInitExpr((Expr *) node->tidquals,
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(PlanState *) tidstate);
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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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* open the base relation and acquire appropriate lock on it.
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*/
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currentRelation = ExecOpenScanRelation(estate, node->scan.scanrelid);
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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));
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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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