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Commit7a36937

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Reimplement hash index locking algorithms, per my recent proposal to
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 inhash index operations. Hash indexes are still not really ready for primetime (since they aren't WAL-logged), but this is a step forward.
1 parentca43f71 commit7a36937

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11 files changed

+1039
-1023
lines changed

11 files changed

+1039
-1023
lines changed

‎src/backend/access/hash/README‎

Lines changed: 2 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -1,4 +1,4 @@
1-
$Header: /cvsroot/pgsql/src/backend/access/hash/README,v 1.2 2003/09/02 03:29:01 tgl Exp $
1+
$Header: /cvsroot/pgsql/src/backend/access/hash/README,v 1.3 2003/09/04 22:06:27 tgl Exp $
22

33
This directory contains an implementation of hash indexing for Postgres.
44

@@ -229,8 +229,8 @@ existing bucket in two, thereby lowering the fill ratio:
229229
check split still needed
230230
if split not needed anymore, drop locks and exit
231231
decide which bucket to split
232-
Attempt to X-lock new bucket number (shouldn't fail, but...)
233232
Attempt to X-lock old bucket number (definitely could fail)
233+
Attempt to X-lock new bucket number (shouldn't fail, but...)
234234
if above fail, drop locks and exit
235235
update meta page to reflect new number of buckets
236236
write/release meta page
@@ -261,12 +261,6 @@ not be overfull and split attempts will stop. (We could make a successful
261261
splitter loop to see if the index is still overfull, but it seems better to
262262
distribute the split overhead across successive insertions.)
263263

264-
It may be wise to make the initial exclusive-lock-page-zero operation a
265-
conditional one as well, although the odds of a deadlock failure are quite
266-
low. (AFAICS it could only deadlock against a VACUUM operation that is
267-
trying to X-lock a bucket that the current process has a stopped indexscan
268-
in.)
269-
270264
A problem is that if a split fails partway through (eg due to insufficient
271265
disk space) the index is left corrupt. The probability of that could be
272266
made quite low if we grab a free page or two before we update the meta

‎src/backend/access/hash/hash.c‎

Lines changed: 88 additions & 86 deletions
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,7 @@
88
*
99
*
1010
* IDENTIFICATION
11-
* $Header: /cvsroot/pgsql/src/backend/access/hash/hash.c,v 1.67 2003/09/02 18:13:29 tgl Exp $
11+
* $Header: /cvsroot/pgsql/src/backend/access/hash/hash.c,v 1.68 2003/09/04 22:06:27 tgl Exp $
1212
*
1313
* NOTES
1414
* This file contains only the public interface routines.
@@ -27,9 +27,6 @@
2727
#include"miscadmin.h"
2828

2929

30-
boolBuildingHash= false;
31-
32-
3330
/* Working state for hashbuild and its callback */
3431
typedefstruct
3532
{
@@ -61,9 +58,6 @@ hashbuild(PG_FUNCTION_ARGS)
6158
doublereltuples;
6259
HashBuildStatebuildstate;
6360

64-
/* set flag to disable locking */
65-
BuildingHash= true;
66-
6761
/*
6862
* We expect to be called exactly once for any index relation. If
6963
* that's not the case, big trouble's what we have.
@@ -82,9 +76,6 @@ hashbuild(PG_FUNCTION_ARGS)
8276
reltuples=IndexBuildHeapScan(heap,index,indexInfo,
8377
hashbuildCallback, (void*)&buildstate);
8478

85-
/* all done */
86-
BuildingHash= false;
87-
8879
/*
8980
* Since we just counted the tuples in the heap, we update its stats
9081
* in pg_class to guarantee that the planner takes advantage of the
@@ -212,10 +203,18 @@ hashgettuple(PG_FUNCTION_ARGS)
212203
IndexScanDescscan= (IndexScanDesc)PG_GETARG_POINTER(0);
213204
ScanDirectiondir= (ScanDirection)PG_GETARG_INT32(1);
214205
HashScanOpaqueso= (HashScanOpaque)scan->opaque;
206+
Relationrel=scan->indexRelation;
215207
Pagepage;
216208
OffsetNumberoffnum;
217209
boolres;
218210

211+
/*
212+
* We hold pin but not lock on current buffer while outside the hash AM.
213+
* Reacquire the read lock here.
214+
*/
215+
if (BufferIsValid(so->hashso_curbuf))
216+
_hash_chgbufaccess(rel,so->hashso_curbuf,HASH_NOLOCK,HASH_READ);
217+
219218
/*
220219
* If we've already initialized this scan, we can just advance it in
221220
* the appropriate direction. If we haven't done so yet, we call a
@@ -267,6 +266,10 @@ hashgettuple(PG_FUNCTION_ARGS)
267266
}
268267
}
269268

269+
/* Release read lock on current buffer, but keep it pinned */
270+
if (BufferIsValid(so->hashso_curbuf))
271+
_hash_chgbufaccess(rel,so->hashso_curbuf,HASH_READ,HASH_NOLOCK);
272+
270273
PG_RETURN_BOOL(res);
271274
}
272275

@@ -285,6 +288,8 @@ hashbeginscan(PG_FUNCTION_ARGS)
285288

286289
scan=RelationGetIndexScan(rel,keysz,scankey);
287290
so= (HashScanOpaque)palloc(sizeof(HashScanOpaqueData));
291+
so->hashso_bucket_valid= false;
292+
so->hashso_bucket_blkno=0;
288293
so->hashso_curbuf=so->hashso_mrkbuf=InvalidBuffer;
289294
scan->opaque=so;
290295

@@ -303,28 +308,38 @@ hashrescan(PG_FUNCTION_ARGS)
303308
IndexScanDescscan= (IndexScanDesc)PG_GETARG_POINTER(0);
304309
ScanKeyscankey= (ScanKey)PG_GETARG_POINTER(1);
305310
HashScanOpaqueso= (HashScanOpaque)scan->opaque;
306-
ItemPointeriptr;
311+
Relationrel=scan->indexRelation;
307312

308-
/* wehold a read lock on the current page in the scan */
309-
if (ItemPointerIsValid(iptr=&(scan->currentItemData)))
313+
/*ifweare called from beginscan, so is still NULL */
314+
if (so)
310315
{
311-
_hash_relbuf(scan->indexRelation,so->hashso_curbuf,HASH_READ);
316+
/* release any pins we still hold */
317+
if (BufferIsValid(so->hashso_curbuf))
318+
_hash_dropbuf(rel,so->hashso_curbuf);
312319
so->hashso_curbuf=InvalidBuffer;
313-
ItemPointerSetInvalid(iptr);
314-
}
315-
if (ItemPointerIsValid(iptr=&(scan->currentMarkData)))
316-
{
317-
_hash_relbuf(scan->indexRelation,so->hashso_mrkbuf,HASH_READ);
320+
321+
if (BufferIsValid(so->hashso_mrkbuf))
322+
_hash_dropbuf(rel,so->hashso_mrkbuf);
318323
so->hashso_mrkbuf=InvalidBuffer;
319-
ItemPointerSetInvalid(iptr);
324+
325+
/* release lock on bucket, too */
326+
if (so->hashso_bucket_blkno)
327+
_hash_droplock(rel,so->hashso_bucket_blkno,HASH_SHARE);
328+
so->hashso_bucket_blkno=0;
320329
}
321330

331+
/* set positions invalid (this will cause _hash_first call) */
332+
ItemPointerSetInvalid(&(scan->currentItemData));
333+
ItemPointerSetInvalid(&(scan->currentMarkData));
334+
322335
/* Update scan key, if a new one is given */
323336
if (scankey&&scan->numberOfKeys>0)
324337
{
325338
memmove(scan->keyData,
326339
scankey,
327340
scan->numberOfKeys*sizeof(ScanKeyData));
341+
if (so)
342+
so->hashso_bucket_valid= false;
328343
}
329344

330345
PG_RETURN_VOID();
@@ -337,32 +352,32 @@ Datum
337352
hashendscan(PG_FUNCTION_ARGS)
338353
{
339354
IndexScanDescscan= (IndexScanDesc)PG_GETARG_POINTER(0);
340-
ItemPointeriptr;
341-
HashScanOpaqueso;
355+
HashScanOpaqueso= (HashScanOpaque)scan->opaque;
356+
Relationrel=scan->indexRelation;
342357

343-
so= (HashScanOpaque)scan->opaque;
358+
/* don't need scan registered anymore */
359+
_hash_dropscan(scan);
344360

345-
/* release any locks we still hold */
346-
if (ItemPointerIsValid(iptr=&(scan->currentItemData)))
347-
{
348-
_hash_relbuf(scan->indexRelation,so->hashso_curbuf,HASH_READ);
349-
so->hashso_curbuf=InvalidBuffer;
350-
ItemPointerSetInvalid(iptr);
351-
}
361+
/* release any pins we still hold */
362+
if (BufferIsValid(so->hashso_curbuf))
363+
_hash_dropbuf(rel,so->hashso_curbuf);
364+
so->hashso_curbuf=InvalidBuffer;
352365

353-
if (ItemPointerIsValid(iptr=&(scan->currentMarkData)))
354-
{
355-
if (BufferIsValid(so->hashso_mrkbuf))
356-
_hash_relbuf(scan->indexRelation,so->hashso_mrkbuf,HASH_READ);
357-
so->hashso_mrkbuf=InvalidBuffer;
358-
ItemPointerSetInvalid(iptr);
359-
}
366+
if (BufferIsValid(so->hashso_mrkbuf))
367+
_hash_dropbuf(rel,so->hashso_mrkbuf);
368+
so->hashso_mrkbuf=InvalidBuffer;
360369

361-
/* don't need scan registered anymore */
362-
_hash_dropscan(scan);
370+
/* release lock on bucket, too */
371+
if (so->hashso_bucket_blkno)
372+
_hash_droplock(rel,so->hashso_bucket_blkno,HASH_SHARE);
373+
so->hashso_bucket_blkno=0;
363374

364375
/* be tidy */
365-
pfree(scan->opaque);
376+
ItemPointerSetInvalid(&(scan->currentItemData));
377+
ItemPointerSetInvalid(&(scan->currentMarkData));
378+
379+
pfree(so);
380+
scan->opaque=NULL;
366381

367382
PG_RETURN_VOID();
368383
}
@@ -374,25 +389,21 @@ Datum
374389
hashmarkpos(PG_FUNCTION_ARGS)
375390
{
376391
IndexScanDescscan= (IndexScanDesc)PG_GETARG_POINTER(0);
377-
ItemPointeriptr;
378-
HashScanOpaqueso;
379-
380-
so= (HashScanOpaque)scan->opaque;
392+
HashScanOpaqueso= (HashScanOpaque)scan->opaque;
393+
Relationrel=scan->indexRelation;
381394

382-
/* release lock on old marked data, if any */
383-
if (ItemPointerIsValid(iptr=&(scan->currentMarkData)))
384-
{
385-
_hash_relbuf(scan->indexRelation,so->hashso_mrkbuf,HASH_READ);
386-
so->hashso_mrkbuf=InvalidBuffer;
387-
ItemPointerSetInvalid(iptr);
388-
}
395+
/* release pin on old marked data, if any */
396+
if (BufferIsValid(so->hashso_mrkbuf))
397+
_hash_dropbuf(rel,so->hashso_mrkbuf);
398+
so->hashso_mrkbuf=InvalidBuffer;
399+
ItemPointerSetInvalid(&(scan->currentMarkData));
389400

390-
/* bumplock on currentItemData and copy to currentMarkData */
401+
/* bumppin count on currentItemData and copy to currentMarkData */
391402
if (ItemPointerIsValid(&(scan->currentItemData)))
392403
{
393-
so->hashso_mrkbuf=_hash_getbuf(scan->indexRelation,
404+
so->hashso_mrkbuf=_hash_getbuf(rel,
394405
BufferGetBlockNumber(so->hashso_curbuf),
395-
HASH_READ);
406+
HASH_NOLOCK);
396407
scan->currentMarkData=scan->currentItemData;
397408
}
398409

@@ -406,26 +417,21 @@ Datum
406417
hashrestrpos(PG_FUNCTION_ARGS)
407418
{
408419
IndexScanDescscan= (IndexScanDesc)PG_GETARG_POINTER(0);
409-
ItemPointeriptr;
410-
HashScanOpaqueso;
420+
HashScanOpaqueso= (HashScanOpaque)scan->opaque;
421+
Relationrel=scan->indexRelation;
411422

412-
so= (HashScanOpaque)scan->opaque;
423+
/* release pin on current data, if any */
424+
if (BufferIsValid(so->hashso_curbuf))
425+
_hash_dropbuf(rel,so->hashso_curbuf);
426+
so->hashso_curbuf=InvalidBuffer;
427+
ItemPointerSetInvalid(&(scan->currentItemData));
413428

414-
/* release lock on current data, if any */
415-
if (ItemPointerIsValid(iptr=&(scan->currentItemData)))
416-
{
417-
_hash_relbuf(scan->indexRelation,so->hashso_curbuf,HASH_READ);
418-
so->hashso_curbuf=InvalidBuffer;
419-
ItemPointerSetInvalid(iptr);
420-
}
421-
422-
/* bump lock on currentMarkData and copy to currentItemData */
429+
/* bump pin count on currentMarkData and copy to currentItemData */
423430
if (ItemPointerIsValid(&(scan->currentMarkData)))
424431
{
425-
so->hashso_curbuf=_hash_getbuf(scan->indexRelation,
432+
so->hashso_curbuf=_hash_getbuf(rel,
426433
BufferGetBlockNumber(so->hashso_mrkbuf),
427-
HASH_READ);
428-
434+
HASH_NOLOCK);
429435
scan->currentItemData=scan->currentMarkData;
430436
}
431437

@@ -474,7 +480,7 @@ hashbulkdelete(PG_FUNCTION_ARGS)
474480
orig_maxbucket=metap->hashm_maxbucket;
475481
orig_ntuples=metap->hashm_ntuples;
476482
memcpy(&local_metapage,metap,sizeof(local_metapage));
477-
_hash_relbuf(rel,metabuf,HASH_READ);
483+
_hash_relbuf(rel,metabuf);
478484

479485
/* Scan the buckets that we know exist */
480486
cur_bucket=0;
@@ -490,7 +496,12 @@ hashbulkdelete(PG_FUNCTION_ARGS)
490496
/* Get address of bucket's start page */
491497
bucket_blkno=BUCKET_TO_BLKNO(&local_metapage,cur_bucket);
492498

493-
/* XXX lock bucket here */
499+
/* Exclusive-lock the bucket so we can shrink it */
500+
_hash_getlock(rel,bucket_blkno,HASH_EXCLUSIVE);
501+
502+
/* Shouldn't have any active scans locally, either */
503+
if (_hash_has_active_scan(rel,cur_bucket))
504+
elog(ERROR,"hash index has active scan during VACUUM");
494505

495506
/* Scan each page in bucket */
496507
blkno=bucket_blkno;
@@ -522,13 +533,6 @@ hashbulkdelete(PG_FUNCTION_ARGS)
522533
htup=&(hitem->hash_itup.t_tid);
523534
if (callback(htup,callback_state))
524535
{
525-
ItemPointerDataindextup;
526-
527-
/* adjust any active scans that will be affected */
528-
/* (this should be unnecessary) */
529-
ItemPointerSet(&indextup,blkno,offno);
530-
_hash_adjscans(rel,&indextup);
531-
532536
/* delete the item from the page */
533537
PageIndexTupleDelete(page,offno);
534538
bucket_dirty=page_dirty= true;
@@ -547,24 +551,22 @@ hashbulkdelete(PG_FUNCTION_ARGS)
547551
}
548552

549553
/*
550-
* Write or free page if needed, advance to next page. We want
551-
* to preserve the invariant that overflow pages are nonempty.
554+
* Write page if needed, advance to next page.
552555
*/
553556
blkno=opaque->hasho_nextblkno;
554557

555-
if (PageIsEmpty(page)&& (opaque->hasho_flag&LH_OVERFLOW_PAGE))
556-
_hash_freeovflpage(rel,buf);
557-
elseif (page_dirty)
558+
if (page_dirty)
558559
_hash_wrtbuf(rel,buf);
559560
else
560-
_hash_relbuf(rel,buf,HASH_WRITE);
561+
_hash_relbuf(rel,buf);
561562
}
562563

563564
/* If we deleted anything, try to compact free space */
564565
if (bucket_dirty)
565566
_hash_squeezebucket(rel,cur_bucket,bucket_blkno);
566567

567-
/* XXX unlock bucket here */
568+
/* Release bucket lock */
569+
_hash_droplock(rel,bucket_blkno,HASH_EXCLUSIVE);
568570

569571
/* Advance to next bucket */
570572
cur_bucket++;
@@ -580,7 +582,7 @@ hashbulkdelete(PG_FUNCTION_ARGS)
580582
/* There's been a split, so process the additional bucket(s) */
581583
cur_maxbucket=metap->hashm_maxbucket;
582584
memcpy(&local_metapage,metap,sizeof(local_metapage));
583-
_hash_relbuf(rel,metabuf,HASH_WRITE);
585+
_hash_relbuf(rel,metabuf);
584586
gotoloop_top;
585587
}
586588

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