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Reimplement hash index locking algorithms, per my recent proposal to

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pghackers.  This fixes the problem recently reported by Markus KrÌutner
(hash bucket split corrupts the state of scans being done concurrently),
and I believe it also fixes all the known problems with deadlocks in
hash index operations.  Hash indexes are still not really ready for prime
time (since they aren't WAL-logged), but this is a step forward.
This commit is contained in:
Tom Lane
2003-09-04 22:06:27 +00:00
parent ca43f71ca5
commit 7a3693716d
11 changed files with 1052 additions and 1036 deletions
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100
src/backend/access/hash/hashscan.c
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@@ -8,22 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/access/hash/hashscan.c,v 1.30 2003/08/04 02:39:57 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.
* $Header: /cvsroot/pgsql/src/backend/access/hash/hashscan.c,v 1.31 2003/09/04 22:06:27 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -44,10 +29,6 @@ typedef HashScanListData *HashScanList;
static HashScanList HashScans = (HashScanList) NULL;
static void _hash_scandel(IndexScanDesc scan,
BlockNumber blkno, OffsetNumber offno);
/*
* AtEOXact_hash() --- clean up hash subsystem at xact abort or commit.
*
@@ -67,9 +48,6 @@ AtEOXact_hash(void)
* at end of transaction anyway.
*/
HashScans = NULL;
/* If we were building a hash, we ain't anymore. */
BuildingHash = false;
}
/*
@@ -112,70 +90,26 @@ _hash_dropscan(IndexScanDesc scan)
pfree(chk);
}
void
_hash_adjscans(Relation rel, ItemPointer tid)
/*
* Is there an active scan in this bucket?
*/
bool
_hash_has_active_scan(Relation rel, Bucket bucket)
{
Oid relid = RelationGetRelid(rel);
HashScanList l;
Oid relid;
relid = RelationGetRelid(rel);
for (l = HashScans; l != (HashScanList) NULL; l = l->hashsl_next)
for (l = HashScans; l != NULL; l = l->hashsl_next)
{
if (relid == l->hashsl_scan->indexRelation->rd_id)
_hash_scandel(l->hashsl_scan, ItemPointerGetBlockNumber(tid),
ItemPointerGetOffsetNumber(tid));
}
}
static void
_hash_scandel(IndexScanDesc scan, BlockNumber blkno, OffsetNumber offno)
{
ItemPointer current;
ItemPointer mark;
Buffer buf;
Buffer metabuf;
HashScanOpaque so;
so = (HashScanOpaque) scan->opaque;
current = &(scan->currentItemData);
mark = &(scan->currentMarkData);
if (ItemPointerIsValid(current)
&& ItemPointerGetBlockNumber(current) == blkno
&& ItemPointerGetOffsetNumber(current) >= offno)
{
metabuf = _hash_getbuf(scan->indexRelation, HASH_METAPAGE, HASH_READ);
buf = so->hashso_curbuf;
_hash_step(scan, &buf, BackwardScanDirection, metabuf);
}
if (ItemPointerIsValid(mark)
&& ItemPointerGetBlockNumber(mark) == blkno
&& ItemPointerGetOffsetNumber(mark) >= offno)
{
/*
* The idea here is to exchange the current and mark positions,
* then step backwards (affecting current), then exchange again.
*/
ItemPointerData tmpitem;
Buffer tmpbuf;
tmpitem = *mark;
*mark = *current;
*current = tmpitem;
tmpbuf = so->hashso_mrkbuf;
so->hashso_mrkbuf = so->hashso_curbuf;
so->hashso_curbuf = tmpbuf;
metabuf = _hash_getbuf(scan->indexRelation, HASH_METAPAGE, HASH_READ);
buf = so->hashso_curbuf;
_hash_step(scan, &buf, BackwardScanDirection, metabuf);
tmpitem = *mark;
*mark = *current;
*current = tmpitem;
tmpbuf = so->hashso_mrkbuf;
so->hashso_mrkbuf = so->hashso_curbuf;
so->hashso_curbuf = tmpbuf;
{
HashScanOpaque so = (HashScanOpaque) l->hashsl_scan->opaque;
if (so->hashso_bucket_valid &&
so->hashso_bucket == bucket)
return true;
}
}
return false;
}