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272 lines
6.8 KiB
C
272 lines
6.8 KiB
C
/*-------------------------------------------------------------------------
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*
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* genam.c
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* general index access method routines
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*
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* 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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* $Header: /cvsroot/pgsql/src/backend/access/index/genam.c,v 1.19 1999/07/15 23:02:58 momjian Exp $
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*
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* NOTES
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* many of the old access method routines have been turned into
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* macros and moved to genam.h -cim 4/30/91
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*
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*-------------------------------------------------------------------------
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*/
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/*
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* OLD COMMENTS
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* Scans are implemented as follows:
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*
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* `0' represents an invalid item pointer.
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* `-' represents an unknown item pointer.
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* `X' represents a known item pointers.
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* `+' represents known or invalid item pointers.
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* `*' represents any item pointers.
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*
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* State is represented by a triple of these symbols in the order of
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* previous, current, next. Note that the case of reverse scans works
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* identically.
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*
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* State Result
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* (1) + + - + 0 0 (if the next item pointer is invalid)
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* (2) + X - (otherwise)
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* (3) * 0 0 * 0 0 (no change)
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* (4) + X 0 X 0 0 (shift)
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* (5) * + X + X - (shift, add unknown)
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*
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* All other states cannot occur.
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*
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* Note:
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*It would be possible to cache the status of the previous and
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* next item pointer using the flags.
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* ----------------------------------------------------------------
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*/
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#include "postgres.h"
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#include "access/genam.h"
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#ifndef HAVE_MEMMOVE
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#else
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#include <string.h>
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#endif
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/* ----------------------------------------------------------------
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* general access method routines
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*
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* All indexed access methods use an identical scan structure.
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* We don't know how the various AMs do locking, however, so we don't
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* do anything about that here.
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*
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* The intent is that an AM implementor will define a front-end routine
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* that calls this one, to fill in the scan, and then does whatever kind
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* of locking he wants.
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* ----------------------------------------------------------------
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*/
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/* ----------------
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* RelationGetIndexScan -- Create and fill an IndexScanDesc.
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*
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* This routine creates an index scan structure and sets its contents
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* up correctly. This routine calls AMrescan to set up the scan with
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* the passed key.
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*
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* Parameters:
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* relation -- index relation for scan.
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* scanFromEnd -- if true, begin scan at one of the index's
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* endpoints.
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* numberOfKeys -- count of scan keys (more than one won't
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* necessarily do anything useful, yet).
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* key -- the ScanKey for the starting position of the scan.
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*
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* Returns:
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* An initialized IndexScanDesc.
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*
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* Side Effects:
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* Bumps the ref count on the relation to keep it in the cache.
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*
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* ----------------
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*/
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IndexScanDesc
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RelationGetIndexScan(Relation relation,
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bool scanFromEnd,
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uint16 numberOfKeys,
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ScanKey key)
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{
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IndexScanDesc scan;
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if (!RelationIsValid(relation))
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elog(ERROR, "RelationGetIndexScan: relation invalid");
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scan = (IndexScanDesc) palloc(sizeof(IndexScanDescData));
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scan->relation = relation;
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scan->opaque = NULL;
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scan->numberOfKeys = numberOfKeys;
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ItemPointerSetInvalid(&scan->previousItemData);
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ItemPointerSetInvalid(&scan->currentItemData);
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ItemPointerSetInvalid(&scan->nextItemData);
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ItemPointerSetInvalid(&scan->previousMarkData);
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ItemPointerSetInvalid(&scan->currentMarkData);
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ItemPointerSetInvalid(&scan->nextMarkData);
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if (numberOfKeys > 0)
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scan->keyData = (ScanKey) palloc(sizeof(ScanKeyData) * numberOfKeys);
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else
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scan->keyData = NULL;
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index_rescan(scan, scanFromEnd, key);
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return scan;
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}
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#ifdef NOT_USED
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/* ----------------
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* IndexScanRestart -- Restart an index scan.
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*
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* This routine isn't used by any existing access method. It's
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* appropriate if relation level locks are what you want.
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*
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* Returns:
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* None.
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*
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* Side Effects:
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* None.
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* ----------------
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*/
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void
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IndexScanRestart(IndexScanDesc scan,
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bool scanFromEnd,
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ScanKey key)
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{
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if (!IndexScanIsValid(scan))
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elog(ERROR, "IndexScanRestart: invalid scan");
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ItemPointerSetInvalid(&scan->previousItemData);
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ItemPointerSetInvalid(&scan->currentItemData);
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ItemPointerSetInvalid(&scan->nextItemData);
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if (RelationGetNumberOfBlocks(scan->relation) == 0)
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scan->flags = ScanUnmarked;
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else if (scanFromEnd)
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scan->flags = ScanUnmarked | ScanUncheckedPrevious;
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else
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scan->flags = ScanUnmarked | ScanUncheckedNext;
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scan->scanFromEnd = (bool) scanFromEnd;
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if (scan->numberOfKeys > 0)
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memmove(scan->keyData,
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key,
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scan->numberOfKeys * sizeof(ScanKeyData));
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}
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/* ----------------
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* IndexScanEnd -- End and index scan.
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*
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* This routine is not used by any existing access method, but is
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* suitable for use if you don't want to do sophisticated locking.
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*
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* Returns:
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* None.
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*
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* Side Effects:
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* None.
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* ----------------
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*/
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void
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IndexScanEnd(IndexScanDesc scan)
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{
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if (!IndexScanIsValid(scan))
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elog(ERROR, "IndexScanEnd: invalid scan");
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pfree(scan);
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}
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/* ----------------
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* IndexScanMarkPosition -- Mark current position in a scan.
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*
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* This routine isn't used by any existing access method, but is the
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* one that AM implementors should use, if they don't want to do any
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* special locking. If relation-level locking is sufficient, this is
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* the routine for you.
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*
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* Returns:
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* None.
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*
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* Side Effects:
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* None.
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* ----------------
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*/
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void
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IndexScanMarkPosition(IndexScanDesc scan)
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{
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RetrieveIndexResult result;
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if (scan->flags & ScanUncheckedPrevious)
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{
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result = index_getnext(scan, BackwardScanDirection);
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if (result != NULL)
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{
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scan->previousItemData = result->index_iptr;
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pfree(result);
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}
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else
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ItemPointerSetInvalid(&scan->previousItemData);
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}
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else if (scan->flags & ScanUncheckedNext)
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{
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result = (RetrieveIndexResult)
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index_getnext(scan, ForwardScanDirection);
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if (result != NULL)
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{
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scan->nextItemData = result->index_iptr;
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pfree(result);
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}
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else
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ItemPointerSetInvalid(&scan->nextItemData);
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}
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scan->previousMarkData = scan->previousItemData;
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scan->currentMarkData = scan->currentItemData;
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scan->nextMarkData = scan->nextItemData;
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scan->flags = 0x0; /* XXX should have a symbolic name */
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}
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/* ----------------
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* IndexScanRestorePosition -- Restore position on a marked scan.
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*
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* This routine isn't used by any existing access method, but is the
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* one that AM implementors should use if they don't want to do any
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* special locking. If relation-level locking is sufficient, then
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* this is the one you want.
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*
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* Returns:
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* None.
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*
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* Side Effects:
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* None.
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* ----------------
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*/
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void
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IndexScanRestorePosition(IndexScanDesc scan)
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{
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if (scan->flags & ScanUnmarked)
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elog(ERROR, "IndexScanRestorePosition: no mark to restore");
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scan->previousItemData = scan->previousMarkData;
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scan->currentItemData = scan->currentMarkData;
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scan->nextItemData = scan->nextMarkData;
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scan->flags = 0x0; /* XXX should have a symbolic name */
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}
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#endif
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