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Commit4974d7f

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Handle parallel index builds on mapped relations.
Commit9da0cc3, which introduced parallel CREATE INDEX, failed topropagate relmapper.c backend local cache state to parallel workerprocesses. This could result in parallel index builds against mappedcatalog relations where the leader process (participating as a worker)scans the new, pristine relfilenode, while worker processes scan theobsolescent relfilenode. When this happened, the final index structurewas typically not consistent with the owning table's structure. Thefinal index structure could contain entries formed from both heaprelfilenodes. Only rebuilds on mapped catalog relations that occur aspart of a VACUUM FULL or CLUSTER could become corrupt in practice, sincetheir mapped relation relfilenode swap is what allows the inconsistencyto arise.On master, fix the problem by propagating the required relmapper.cbackend state as part of standard parallel initialization (Cf. commit29d58fd). On v11, simply disallow builds against mapped catalogrelations by deeming them parallel unsafe.Author: Peter GeogheganReported-By: "death lock"Reviewed-By: Tom Lane, Amit KapilaBug: #15309Discussion:https://postgr.es/m/153329671686.1405.18298309097348420351@wrigleys.postgresql.orgBackpatch: 11-, where parallel CREATE INDEX was introduced.
1 parentd4a9004 commit4974d7f

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5 files changed

+107
-10
lines changed

5 files changed

+107
-10
lines changed

‎src/backend/access/transam/README.parallel

Lines changed: 4 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -125,6 +125,10 @@ worker. This includes:
125125
- State related to pending REINDEX operations, which prevents access to
126126
an index that is currently being rebuilt.
127127

128+
- Active relmapper.c mapping state. This is needed to allow consistent
129+
answers when fetching the current relfilenode for relation oids of
130+
mapped relations.
131+
128132
To prevent unprincipled deadlocks when running in parallel mode, this code
129133
also arranges for the leader and all workers to participate in group
130134
locking. See src/backend/storage/lmgr/README for more details.

‎src/backend/access/transam/parallel.c

Lines changed: 18 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -37,6 +37,7 @@
3737
#include"utils/guc.h"
3838
#include"utils/inval.h"
3939
#include"utils/memutils.h"
40+
#include"utils/relmapper.h"
4041
#include"utils/snapmgr.h"
4142
#include"utils/typcache.h"
4243

@@ -69,6 +70,7 @@
6970
#definePARALLEL_KEY_ENTRYPOINTUINT64CONST(0xFFFFFFFFFFFF0009)
7071
#definePARALLEL_KEY_SESSION_DSMUINT64CONST(0xFFFFFFFFFFFF000A)
7172
#definePARALLEL_KEY_REINDEX_STATEUINT64CONST(0xFFFFFFFFFFFF000B)
73+
#definePARALLEL_KEY_RELMAPPER_STATEUINT64CONST(0xFFFFFFFFFFFF000C)
7274

7375
/* Fixed-size parallel state. */
7476
typedefstructFixedParallelState
@@ -205,6 +207,7 @@ InitializeParallelDSM(ParallelContext *pcxt)
205207
Sizeasnaplen=0;
206208
Sizetstatelen=0;
207209
Sizereindexlen=0;
210+
Sizerelmapperlen=0;
208211
Sizesegsize=0;
209212
inti;
210213
FixedParallelState*fps;
@@ -256,8 +259,10 @@ InitializeParallelDSM(ParallelContext *pcxt)
256259
shm_toc_estimate_chunk(&pcxt->estimator,sizeof(dsm_handle));
257260
reindexlen=EstimateReindexStateSpace();
258261
shm_toc_estimate_chunk(&pcxt->estimator,reindexlen);
262+
relmapperlen=EstimateRelationMapSpace();
263+
shm_toc_estimate_chunk(&pcxt->estimator,relmapperlen);
259264
/* If you add more chunks here, you probably need to add keys. */
260-
shm_toc_estimate_keys(&pcxt->estimator,8);
265+
shm_toc_estimate_keys(&pcxt->estimator,9);
261266

262267
/* Estimate space need for error queues. */
263268
StaticAssertStmt(BUFFERALIGN(PARALLEL_ERROR_QUEUE_SIZE)==
@@ -327,6 +332,7 @@ InitializeParallelDSM(ParallelContext *pcxt)
327332
char*asnapspace;
328333
char*tstatespace;
329334
char*reindexspace;
335+
char*relmapperspace;
330336
char*error_queue_space;
331337
char*session_dsm_handle_space;
332338
char*entrypointstate;
@@ -373,6 +379,12 @@ InitializeParallelDSM(ParallelContext *pcxt)
373379
SerializeReindexState(reindexlen,reindexspace);
374380
shm_toc_insert(pcxt->toc,PARALLEL_KEY_REINDEX_STATE,reindexspace);
375381

382+
/* Serialize relmapper state. */
383+
relmapperspace=shm_toc_allocate(pcxt->toc,relmapperlen);
384+
SerializeRelationMap(relmapperlen,relmapperspace);
385+
shm_toc_insert(pcxt->toc,PARALLEL_KEY_RELMAPPER_STATE,
386+
relmapperspace);
387+
376388
/* Allocate space for worker information. */
377389
pcxt->worker=palloc0(sizeof(ParallelWorkerInfo)*pcxt->nworkers);
378390

@@ -1205,6 +1217,7 @@ ParallelWorkerMain(Datum main_arg)
12051217
char*asnapspace;
12061218
char*tstatespace;
12071219
char*reindexspace;
1220+
char*relmapperspace;
12081221
StringInfoDatamsgbuf;
12091222
char*session_dsm_handle_space;
12101223

@@ -1380,6 +1393,10 @@ ParallelWorkerMain(Datum main_arg)
13801393
reindexspace=shm_toc_lookup(toc,PARALLEL_KEY_REINDEX_STATE, false);
13811394
RestoreReindexState(reindexspace);
13821395

1396+
/* Restore relmapper state. */
1397+
relmapperspace=shm_toc_lookup(toc,PARALLEL_KEY_RELMAPPER_STATE, false);
1398+
RestoreRelationMap(relmapperspace);
1399+
13831400
/*
13841401
* We've initialized all of our state now; nothing should change
13851402
* hereafter.

‎src/backend/access/transam/xact.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -2018,7 +2018,7 @@ CommitTransaction(void)
20182018
HOLD_INTERRUPTS();
20192019

20202020
/* Commit updates to the relation map --- do this as late as possible */
2021-
AtEOXact_RelationMap(true);
2021+
AtEOXact_RelationMap(true,is_parallel_worker);
20222022

20232023
/*
20242024
* set the current transaction state information appropriately during
@@ -2539,7 +2539,7 @@ AbortTransaction(void)
25392539
AtAbort_Portals();
25402540
AtEOXact_LargeObject(false);
25412541
AtAbort_Notify();
2542-
AtEOXact_RelationMap(false);
2542+
AtEOXact_RelationMap(false,is_parallel_worker);
25432543
AtAbort_Twophase();
25442544

25452545
/*

‎src/backend/utils/cache/relmapper.c

Lines changed: 78 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -91,6 +91,16 @@ typedef struct RelMapFile
9191
int32pad;/* to make the struct size be 512 exactly */
9292
}RelMapFile;
9393

94+
/*
95+
* State for serializing local and shared relmappings for parallel workers
96+
* (active states only). See notes on active_* and pending_* updates state.
97+
*/
98+
typedefstructSerializedActiveRelMaps
99+
{
100+
RelMapFileactive_shared_updates;
101+
RelMapFileactive_local_updates;
102+
}SerializedActiveRelMaps;
103+
94104
/*
95105
* The currently known contents of the shared map file and our database's
96106
* local map file are stored here. These can be reloaded from disk
@@ -111,6 +121,9 @@ static RelMapFile local_map;
111121
* they will become active at the next CommandCounterIncrement. This setup
112122
* lets map updates act similarly to updates of pg_class rows, ie, they
113123
* become visible only at the next CommandCounterIncrement boundary.
124+
*
125+
* Active shared and active local updates are serialized by the parallel
126+
* infrastructure, and deserialized within parallel workers.
114127
*/
115128
staticRelMapFileactive_shared_updates;
116129
staticRelMapFileactive_local_updates;
@@ -263,13 +276,16 @@ RelationMapUpdateMap(Oid relationId, Oid fileNode, bool shared,
263276
else
264277
{
265278
/*
266-
* We don't currently support map changes within subtransactions. This
267-
* could be done with more bookkeeping infrastructure, but it doesn't
268-
* presently seem worth it.
279+
* We don't currently support map changes within subtransactions, or
280+
*when in parallel mode. Thiscould be done with more bookkeeping
281+
*infrastructure, but it doesn'tpresently seem worth it.
269282
*/
270283
if (GetCurrentTransactionNestLevel()>1)
271284
elog(ERROR,"cannot change relation mapping within subtransaction");
272285

286+
if (IsInParallelMode())
287+
elog(ERROR,"cannot change relation mapping in parallel mode");
288+
273289
if (immediate)
274290
{
275291
/* Make it active, but only locally */
@@ -452,11 +468,14 @@ AtCCI_RelationMap(void)
452468
*
453469
* During abort, we just have to throw away any pending map changes.
454470
* Normal post-abort cleanup will take care of fixing relcache entries.
471+
* Parallel worker commit/abort is handled by resetting active mappings
472+
* that may have been received from the leader process. (There should be
473+
* no pending updates in parallel workers.)
455474
*/
456475
void
457-
AtEOXact_RelationMap(boolisCommit)
476+
AtEOXact_RelationMap(boolisCommit,boolisParallelWorker)
458477
{
459-
if (isCommit)
478+
if (isCommit&& !isParallelWorker)
460479
{
461480
/*
462481
* We should not get here with any "pending" updates. (We could
@@ -482,7 +501,10 @@ AtEOXact_RelationMap(bool isCommit)
482501
}
483502
else
484503
{
485-
/* Abort --- drop all local and pending updates */
504+
/* Abort or parallel worker --- drop all local and pending updates */
505+
Assert(!isParallelWorker||pending_shared_updates.num_mappings==0);
506+
Assert(!isParallelWorker||pending_local_updates.num_mappings==0);
507+
486508
active_shared_updates.num_mappings=0;
487509
active_local_updates.num_mappings=0;
488510
pending_shared_updates.num_mappings=0;
@@ -614,6 +636,56 @@ RelationMapInitializePhase3(void)
614636
load_relmap_file(false);
615637
}
616638

639+
/*
640+
* EstimateRelationMapSpace
641+
*
642+
* Estimate space needed to pass active shared and local relmaps to parallel
643+
* workers.
644+
*/
645+
Size
646+
EstimateRelationMapSpace(void)
647+
{
648+
returnsizeof(SerializedActiveRelMaps);
649+
}
650+
651+
/*
652+
* SerializeRelationMap
653+
*
654+
* Serialize active shared and local relmap state for parallel workers.
655+
*/
656+
void
657+
SerializeRelationMap(SizemaxSize,char*startAddress)
658+
{
659+
SerializedActiveRelMaps*relmaps;
660+
661+
Assert(maxSize >=EstimateRelationMapSpace());
662+
663+
relmaps= (SerializedActiveRelMaps*)startAddress;
664+
relmaps->active_shared_updates=active_shared_updates;
665+
relmaps->active_local_updates=active_local_updates;
666+
}
667+
668+
/*
669+
* RestoreRelationMap
670+
*
671+
* Restore active shared and local relmap state within a parallel worker.
672+
*/
673+
void
674+
RestoreRelationMap(char*startAddress)
675+
{
676+
SerializedActiveRelMaps*relmaps;
677+
678+
if (active_shared_updates.num_mappings!=0||
679+
active_local_updates.num_mappings!=0||
680+
pending_shared_updates.num_mappings!=0||
681+
pending_local_updates.num_mappings!=0)
682+
elog(ERROR,"parallel worker has existing mappings");
683+
684+
relmaps= (SerializedActiveRelMaps*)startAddress;
685+
active_shared_updates=relmaps->active_shared_updates;
686+
active_local_updates=relmaps->active_local_updates;
687+
}
688+
617689
/*
618690
* load_relmap_file -- load data from the shared or local map file
619691
*

‎src/include/utils/relmapper.h

Lines changed: 5 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -48,7 +48,7 @@ extern void RelationMapInvalidate(bool shared);
4848
externvoidRelationMapInvalidateAll(void);
4949

5050
externvoidAtCCI_RelationMap(void);
51-
externvoidAtEOXact_RelationMap(boolisCommit);
51+
externvoidAtEOXact_RelationMap(boolisCommit,boolisParallelWorker);
5252
externvoidAtPrepare_RelationMap(void);
5353

5454
externvoidCheckPointRelationMap(void);
@@ -59,6 +59,10 @@ extern void RelationMapInitialize(void);
5959
externvoidRelationMapInitializePhase2(void);
6060
externvoidRelationMapInitializePhase3(void);
6161

62+
externSizeEstimateRelationMapSpace(void);
63+
externvoidSerializeRelationMap(SizemaxSize,char*startAddress);
64+
externvoidRestoreRelationMap(char*startAddress);
65+
6266
externvoidrelmap_redo(XLogReaderState*record);
6367
externvoidrelmap_desc(StringInfobuf,XLogReaderState*record);
6468
externconstchar*relmap_identify(uint8info);

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