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/*-------------------------------------------------------------------------
*
* hashscan.c
* manage scans on hash tables
*
* Portions Copyright (c) 1996-2001, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/hash/hashscan.c,v 1.24 2001/01/24 19:42:47 momjian Exp $
*
* NOTES
* Because we can be doing an index scan on a relation while we
* update it, we need to avoid missing data that moves around in
* the index. The routines and global variables in this file
* guarantee that all scans in the local address space stay
* correctly positioned. This is all we need to worry about, since
* write locking guarantees that no one else will be on the same
* page at the same time as we are.
*
* The scheme is to manage a list of active scans in the current
* backend. Whenever we add or remove records from an index, we
* check the list of active scans to see if any has been affected.
* A scan is affected only if it is on the same relation, and the
* same page, as the update.
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "access/hash.h"
static void _hash_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno);
static bool _hash_scantouched(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno);
typedef struct HashScanListData
{
IndexScanDesc hashsl_scan;
struct HashScanListData *hashsl_next;
} HashScanListData;
typedef HashScanListData *HashScanList;
static HashScanList HashScans = (HashScanList) NULL;
/*
* _Hash_regscan() -- register a new scan.
*/
void
_hash_regscan(IndexScanDesc scan)
{
HashScanList new_el;
new_el = (HashScanList) palloc(sizeof(HashScanListData));
new_el->hashsl_scan = scan;
new_el->hashsl_next = HashScans;
HashScans = new_el;
}
/*
* _hash_dropscan() -- drop a scan from the scan list
*/
void
_hash_dropscan(IndexScanDesc scan)
{
HashScanList chk,
last;
last = (HashScanList) NULL;
for (chk = HashScans;
chk != (HashScanList) NULL && chk->hashsl_scan != scan;
chk = chk->hashsl_next)
last = chk;
if (chk == (HashScanList) NULL)
elog(ERROR, "hash scan list trashed; can't find 0x%p", (void *) scan);
if (last == (HashScanList) NULL)
HashScans = chk->hashsl_next;
else
last->hashsl_next = chk->hashsl_next;
pfree(chk);
}
void
_hash_adjscans(Relation rel, ItemPointer tid)
{
HashScanList l;
Oid relid;
relid = RelationGetRelid(rel);
for (l = HashScans; l != (HashScanList) NULL; l = l->hashsl_next)
{
if (relid == l->hashsl_scan->relation->rd_id)
_hash_scandel(l->hashsl_scan, ItemPointerGetBlockNumber(tid),
ItemPointerGetOffsetNumber(tid));
}
}
static void
_hash_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno)
{
ItemPointer current;
Buffer buf;
Buffer metabuf;
HashScanOpaque so;
if (!_hash_scantouched(scan, blkno, offno))
return;
metabuf = _hash_getbuf(scan->relation, HASH_METAPAGE, HASH_READ);
so = (HashScanOpaque) scan->opaque;
buf = so->hashso_curbuf;
current = &(scan->currentItemData);
if (ItemPointerIsValid(current)
&& ItemPointerGetBlockNumber(current) == blkno
&& ItemPointerGetOffsetNumber(current) >= offno)
{
_hash_step(scan, &buf, BackwardScanDirection, metabuf);
so->hashso_curbuf = buf;
}
current = &(scan->currentMarkData);
if (ItemPointerIsValid(current)
&& ItemPointerGetBlockNumber(current) == blkno
&& ItemPointerGetOffsetNumber(current) >= offno)
{
ItemPointerData tmp;
tmp = *current;
*current = scan->currentItemData;
scan->currentItemData = tmp;
_hash_step(scan, &buf, BackwardScanDirection, metabuf);
so->hashso_mrkbuf = buf;
tmp = *current;
*current = scan->currentItemData;
scan->currentItemData = tmp;
}
}
static bool
_hash_scantouched(IndexScanDesc scan,
BlockNumber blkno,
OffsetNumber offno)
{
ItemPointer current;
current = &(scan->currentItemData);
if (ItemPointerIsValid(current)
&& ItemPointerGetBlockNumber(current) == blkno
&& ItemPointerGetOffsetNumber(current) >= offno)
return true;
current = &(scan->currentMarkData);
if (ItemPointerIsValid(current)
&& ItemPointerGetBlockNumber(current) == blkno
&& ItemPointerGetOffsetNumber(current) >= offno)
return true;
return false;
}
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