From 5330f1df94b1549cef7de1a4d9be2b88a7d2866b Mon Sep 17 00:00:00 2001 From: houzj Date: Thu, 18 Feb 2021 10:02:06 +0800 Subject: [PATCH 1/4] Add new GUC option: enable_parallel_dml (boolean) The current implementation of parallel "INSERT ... SELECT ..." may incur non-negligible overhead in the additional parallel-safety checks that it performs, even when, in the end, those checks determine that parallelism can't be used. This is normally only ever a problem for large complex tables, particularly in the case of when the target table has a large number of partitions. To address this potential isse, a new GUC option "enable_parallel_dml" is added, to allow parallel DML to be enabled/disabled. The default is false. --- src/backend/optimizer/path/costsize.c | 2 ++ src/backend/optimizer/util/clauses.c | 8 ++++++-- src/backend/utils/misc/guc.c | 11 +++++++++++ src/backend/utils/misc/postgresql.conf.sample | 1 + src/include/optimizer/cost.h | 1 + 5 files changed, 21 insertions(+), 2 deletions(-) diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index f7c13be..778f71b 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -129,6 +129,8 @@ Cost disable_cost = 1.0e10; int max_parallel_workers_per_gather = 2; +bool enable_parallel_dml = false; + bool enable_seqscan = true; bool enable_indexscan = true; bool enable_indexonlyscan = true; diff --git a/src/backend/optimizer/util/clauses.c b/src/backend/optimizer/util/clauses.c index de16a28..eb6eee5 100644 --- a/src/backend/optimizer/util/clauses.c +++ b/src/backend/optimizer/util/clauses.c @@ -1219,8 +1219,9 @@ target_rel_max_parallel_hazard_recurse(Relation rel, * table-modification statement. * It's not possible in the following cases: * - * 1) INSERT...ON CONFLICT...DO UPDATE - * 2) INSERT without SELECT + * 1) enable_parallel_dml is off + * 2) INSERT...ON CONFLICT...DO UPDATE + * 3) INSERT without SELECT * * (Note: we don't do in-depth parallel-safety checks here, we do only the * cheaper tests that can quickly exclude obvious cases for which @@ -1236,6 +1237,9 @@ is_parallel_possible_for_modify(Query *parse) Assert(IsModifySupportedInParallelMode(parse->commandType)); + if (!enable_parallel_dml) + return false; + /* * UPDATE is not currently supported in parallel-mode, so prohibit * INSERT...ON CONFLICT...DO UPDATE... diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c index eafdb11..6fdb991 100644 --- a/src/backend/utils/misc/guc.c +++ b/src/backend/utils/misc/guc.c @@ -2048,6 +2048,17 @@ static struct config_bool ConfigureNamesBool[] = NULL, NULL, NULL }, + { + {"enable_parallel_dml", PGC_USERSET, QUERY_TUNING_METHOD, + gettext_noop("Enables the planner's use of parallel plans for table-modification commands."), + NULL, + GUC_EXPLAIN + }, + &enable_parallel_dml, + false, + NULL, NULL, NULL + }, + /* End-of-list marker */ { {NULL, 0, 0, NULL, NULL}, NULL, false, NULL, NULL, NULL diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample index db6db37..fdd1fce 100644 --- a/src/backend/utils/misc/postgresql.conf.sample +++ b/src/backend/utils/misc/postgresql.conf.sample @@ -370,6 +370,7 @@ #enable_partitionwise_aggregate = off #enable_parallel_hash = on #enable_partition_pruning = on +#enable_parallel_dml = off # - Planner Cost Constants - diff --git a/src/include/optimizer/cost.h b/src/include/optimizer/cost.h index 9f15fcb..4af0beb 100644 --- a/src/include/optimizer/cost.h +++ b/src/include/optimizer/cost.h @@ -47,6 +47,7 @@ typedef enum /* parameter variables and flags (see also optimizer.h) */ extern PGDLLIMPORT Cost disable_cost; extern PGDLLIMPORT int max_parallel_workers_per_gather; +extern PGDLLIMPORT bool enable_parallel_dml; extern PGDLLIMPORT bool enable_seqscan; extern PGDLLIMPORT bool enable_indexscan; extern PGDLLIMPORT bool enable_indexonlyscan; -- 2.7.2.windows.1