From 4974d7f87e62a58e80c6524e49677cb25cc10e12 Mon Sep 17 00:00:00 2001 From: Peter Geoghegan Date: Fri, 10 Aug 2018 13:01:34 -0700 Subject: [PATCH] Handle parallel index builds on mapped relations. Commit 9da0cc35284, which introduced parallel CREATE INDEX, failed to propagate relmapper.c backend local cache state to parallel worker processes. This could result in parallel index builds against mapped catalog relations where the leader process (participating as a worker) scans the new, pristine relfilenode, while worker processes scan the obsolescent relfilenode. When this happened, the final index structure was typically not consistent with the owning table's structure. The final index structure could contain entries formed from both heap relfilenodes. Only rebuilds on mapped catalog relations that occur as part of a VACUUM FULL or CLUSTER could become corrupt in practice, since their mapped relation relfilenode swap is what allows the inconsistency to arise. On master, fix the problem by propagating the required relmapper.c backend state as part of standard parallel initialization (Cf. commit 29d58fd3). On v11, simply disallow builds against mapped catalog relations by deeming them parallel unsafe. Author: Peter Geoghegan Reported-By: "death lock" Reviewed-By: Tom Lane, Amit Kapila Bug: #15309 Discussion: https://postgr.es/m/153329671686.1405.18298309097348420351@wrigleys.postgresql.org Backpatch: 11-, where parallel CREATE INDEX was introduced. --- src/backend/access/transam/README.parallel | 4 ++ src/backend/access/transam/parallel.c | 19 ++++- src/backend/access/transam/xact.c | 4 +- src/backend/utils/cache/relmapper.c | 84 ++++++++++++++++++++-- src/include/utils/relmapper.h | 6 +- 5 files changed, 107 insertions(+), 10 deletions(-) diff --git a/src/backend/access/transam/README.parallel b/src/backend/access/transam/README.parallel index f09a580634..85e5840feb 100644 --- a/src/backend/access/transam/README.parallel +++ b/src/backend/access/transam/README.parallel @@ -125,6 +125,10 @@ worker. This includes: - State related to pending REINDEX operations, which prevents access to an index that is currently being rebuilt. + - Active relmapper.c mapping state. This is needed to allow consistent + answers when fetching the current relfilenode for relation oids of + mapped relations. + To prevent unprincipled deadlocks when running in parallel mode, this code also arranges for the leader and all workers to participate in group locking. See src/backend/storage/lmgr/README for more details. diff --git a/src/backend/access/transam/parallel.c b/src/backend/access/transam/parallel.c index 30ddf94c95..c168118467 100644 --- a/src/backend/access/transam/parallel.c +++ b/src/backend/access/transam/parallel.c @@ -37,6 +37,7 @@ #include "utils/guc.h" #include "utils/inval.h" #include "utils/memutils.h" +#include "utils/relmapper.h" #include "utils/snapmgr.h" #include "utils/typcache.h" @@ -69,6 +70,7 @@ #define PARALLEL_KEY_ENTRYPOINT UINT64CONST(0xFFFFFFFFFFFF0009) #define PARALLEL_KEY_SESSION_DSM UINT64CONST(0xFFFFFFFFFFFF000A) #define PARALLEL_KEY_REINDEX_STATE UINT64CONST(0xFFFFFFFFFFFF000B) +#define PARALLEL_KEY_RELMAPPER_STATE UINT64CONST(0xFFFFFFFFFFFF000C) /* Fixed-size parallel state. */ typedef struct FixedParallelState @@ -205,6 +207,7 @@ InitializeParallelDSM(ParallelContext *pcxt) Size asnaplen = 0; Size tstatelen = 0; Size reindexlen = 0; + Size relmapperlen = 0; Size segsize = 0; int i; FixedParallelState *fps; @@ -256,8 +259,10 @@ InitializeParallelDSM(ParallelContext *pcxt) shm_toc_estimate_chunk(&pcxt->estimator, sizeof(dsm_handle)); reindexlen = EstimateReindexStateSpace(); shm_toc_estimate_chunk(&pcxt->estimator, reindexlen); + relmapperlen = EstimateRelationMapSpace(); + shm_toc_estimate_chunk(&pcxt->estimator, relmapperlen); /* If you add more chunks here, you probably need to add keys. */ - shm_toc_estimate_keys(&pcxt->estimator, 8); + shm_toc_estimate_keys(&pcxt->estimator, 9); /* Estimate space need for error queues. */ StaticAssertStmt(BUFFERALIGN(PARALLEL_ERROR_QUEUE_SIZE) == @@ -327,6 +332,7 @@ InitializeParallelDSM(ParallelContext *pcxt) char *asnapspace; char *tstatespace; char *reindexspace; + char *relmapperspace; char *error_queue_space; char *session_dsm_handle_space; char *entrypointstate; @@ -373,6 +379,12 @@ InitializeParallelDSM(ParallelContext *pcxt) SerializeReindexState(reindexlen, reindexspace); shm_toc_insert(pcxt->toc, PARALLEL_KEY_REINDEX_STATE, reindexspace); + /* Serialize relmapper state. */ + relmapperspace = shm_toc_allocate(pcxt->toc, relmapperlen); + SerializeRelationMap(relmapperlen, relmapperspace); + shm_toc_insert(pcxt->toc, PARALLEL_KEY_RELMAPPER_STATE, + relmapperspace); + /* Allocate space for worker information. */ pcxt->worker = palloc0(sizeof(ParallelWorkerInfo) * pcxt->nworkers); @@ -1205,6 +1217,7 @@ ParallelWorkerMain(Datum main_arg) char *asnapspace; char *tstatespace; char *reindexspace; + char *relmapperspace; StringInfoData msgbuf; char *session_dsm_handle_space; @@ -1380,6 +1393,10 @@ ParallelWorkerMain(Datum main_arg) reindexspace = shm_toc_lookup(toc, PARALLEL_KEY_REINDEX_STATE, false); RestoreReindexState(reindexspace); + /* Restore relmapper state. */ + relmapperspace = shm_toc_lookup(toc, PARALLEL_KEY_RELMAPPER_STATE, false); + RestoreRelationMap(relmapperspace); + /* * We've initialized all of our state now; nothing should change * hereafter. diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c index 9aa63c8792..cd8270d5fb 100644 --- a/src/backend/access/transam/xact.c +++ b/src/backend/access/transam/xact.c @@ -2018,7 +2018,7 @@ CommitTransaction(void) HOLD_INTERRUPTS(); /* Commit updates to the relation map --- do this as late as possible */ - AtEOXact_RelationMap(true); + AtEOXact_RelationMap(true, is_parallel_worker); /* * set the current transaction state information appropriately during @@ -2539,7 +2539,7 @@ AbortTransaction(void) AtAbort_Portals(); AtEOXact_LargeObject(false); AtAbort_Notify(); - AtEOXact_RelationMap(false); + AtEOXact_RelationMap(false, is_parallel_worker); AtAbort_Twophase(); /* diff --git a/src/backend/utils/cache/relmapper.c b/src/backend/utils/cache/relmapper.c index c7f0e6f6d4..905867dc76 100644 --- a/src/backend/utils/cache/relmapper.c +++ b/src/backend/utils/cache/relmapper.c @@ -91,6 +91,16 @@ typedef struct RelMapFile int32 pad; /* to make the struct size be 512 exactly */ } RelMapFile; +/* + * State for serializing local and shared relmappings for parallel workers + * (active states only). See notes on active_* and pending_* updates state. + */ +typedef struct SerializedActiveRelMaps +{ + RelMapFile active_shared_updates; + RelMapFile active_local_updates; +} SerializedActiveRelMaps; + /* * The currently known contents of the shared map file and our database's * local map file are stored here. These can be reloaded from disk @@ -111,6 +121,9 @@ static RelMapFile local_map; * they will become active at the next CommandCounterIncrement. This setup * lets map updates act similarly to updates of pg_class rows, ie, they * become visible only at the next CommandCounterIncrement boundary. + * + * Active shared and active local updates are serialized by the parallel + * infrastructure, and deserialized within parallel workers. */ static RelMapFile active_shared_updates; static RelMapFile active_local_updates; @@ -263,13 +276,16 @@ RelationMapUpdateMap(Oid relationId, Oid fileNode, bool shared, else { /* - * We don't currently support map changes within subtransactions. This - * could be done with more bookkeeping infrastructure, but it doesn't - * presently seem worth it. + * We don't currently support map changes within subtransactions, or + * when in parallel mode. This could be done with more bookkeeping + * infrastructure, but it doesn't presently seem worth it. */ if (GetCurrentTransactionNestLevel() > 1) elog(ERROR, "cannot change relation mapping within subtransaction"); + if (IsInParallelMode()) + elog(ERROR, "cannot change relation mapping in parallel mode"); + if (immediate) { /* Make it active, but only locally */ @@ -452,11 +468,14 @@ AtCCI_RelationMap(void) * * During abort, we just have to throw away any pending map changes. * Normal post-abort cleanup will take care of fixing relcache entries. + * Parallel worker commit/abort is handled by resetting active mappings + * that may have been received from the leader process. (There should be + * no pending updates in parallel workers.) */ void -AtEOXact_RelationMap(bool isCommit) +AtEOXact_RelationMap(bool isCommit, bool isParallelWorker) { - if (isCommit) + if (isCommit && !isParallelWorker) { /* * We should not get here with any "pending" updates. (We could @@ -482,7 +501,10 @@ AtEOXact_RelationMap(bool isCommit) } else { - /* Abort --- drop all local and pending updates */ + /* Abort or parallel worker --- drop all local and pending updates */ + Assert(!isParallelWorker || pending_shared_updates.num_mappings == 0); + Assert(!isParallelWorker || pending_local_updates.num_mappings == 0); + active_shared_updates.num_mappings = 0; active_local_updates.num_mappings = 0; pending_shared_updates.num_mappings = 0; @@ -614,6 +636,56 @@ RelationMapInitializePhase3(void) load_relmap_file(false); } +/* + * EstimateRelationMapSpace + * + * Estimate space needed to pass active shared and local relmaps to parallel + * workers. + */ +Size +EstimateRelationMapSpace(void) +{ + return sizeof(SerializedActiveRelMaps); +} + +/* + * SerializeRelationMap + * + * Serialize active shared and local relmap state for parallel workers. + */ +void +SerializeRelationMap(Size maxSize, char *startAddress) +{ + SerializedActiveRelMaps *relmaps; + + Assert(maxSize >= EstimateRelationMapSpace()); + + relmaps = (SerializedActiveRelMaps *) startAddress; + relmaps->active_shared_updates = active_shared_updates; + relmaps->active_local_updates = active_local_updates; +} + +/* + * RestoreRelationMap + * + * Restore active shared and local relmap state within a parallel worker. + */ +void +RestoreRelationMap(char *startAddress) +{ + SerializedActiveRelMaps *relmaps; + + if (active_shared_updates.num_mappings != 0 || + active_local_updates.num_mappings != 0 || + pending_shared_updates.num_mappings != 0 || + pending_local_updates.num_mappings != 0) + elog(ERROR, "parallel worker has existing mappings"); + + relmaps = (SerializedActiveRelMaps *) startAddress; + active_shared_updates = relmaps->active_shared_updates; + active_local_updates = relmaps->active_local_updates; +} + /* * load_relmap_file -- load data from the shared or local map file * diff --git a/src/include/utils/relmapper.h b/src/include/utils/relmapper.h index f69b1006bf..fb51943498 100644 --- a/src/include/utils/relmapper.h +++ b/src/include/utils/relmapper.h @@ -48,7 +48,7 @@ extern void RelationMapInvalidate(bool shared); extern void RelationMapInvalidateAll(void); extern void AtCCI_RelationMap(void); -extern void AtEOXact_RelationMap(bool isCommit); +extern void AtEOXact_RelationMap(bool isCommit, bool isParallelWorker); extern void AtPrepare_RelationMap(void); extern void CheckPointRelationMap(void); @@ -59,6 +59,10 @@ extern void RelationMapInitialize(void); extern void RelationMapInitializePhase2(void); extern void RelationMapInitializePhase3(void); +extern Size EstimateRelationMapSpace(void); +extern void SerializeRelationMap(Size maxSize, char *startAddress); +extern void RestoreRelationMap(char *startAddress); + extern void relmap_redo(XLogReaderState *record); extern void relmap_desc(StringInfo buf, XLogReaderState *record); extern const char *relmap_identify(uint8 info); -- 2.40.0