From 77cd477c4ba885cfa1ba67beaa82e06f2e182b85 Mon Sep 17 00:00:00 2001 From: Robert Haas Date: Tue, 26 Apr 2016 08:31:38 -0400 Subject: [PATCH] Enable parallel query by default. Change max_parallel_degree default from 0 to 2. It is possible that this is not a good idea, or that we should go with 1 worker rather than 2, but we won't find out without trying it. Along the way, reword the documentation for max_parallel_degree a little bit to hopefully make it more clear. Discussion: 20160420174631.3qjjhpwsvvx5bau5@alap3.anarazel.de --- doc/src/sgml/config.sgml | 12 ++++++++---- src/backend/optimizer/path/costsize.c | 2 +- src/backend/utils/misc/guc.c | 2 +- src/backend/utils/misc/postgresql.conf.sample | 2 +- 4 files changed, 11 insertions(+), 7 deletions(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 909b3e23c5..dce1daa73a 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -2005,10 +2005,14 @@ include_dir 'conf.d' - Sets the maximum degree of parallelism for an individual parallel - operation. Note that the requested number of workers may not actually - be available at runtime. Parallel workers are taken from the pool - of processes established by . + Sets the maximum number of workers that can be started for an + individual parallel operation. Parallel workers are taken from the + pool of processes established by + . Note that the requested + number of workers may not actually be available at runtime. If this + occurs, the plan will run with fewer workers than expected, which may + be inefficient. The default value is 2. Setting this value to 0 + disables parallel query. diff --git a/src/backend/optimizer/path/costsize.c b/src/backend/optimizer/path/costsize.c index 4917922ab5..fcb18732d8 100644 --- a/src/backend/optimizer/path/costsize.c +++ b/src/backend/optimizer/path/costsize.c @@ -113,7 +113,7 @@ int effective_cache_size = DEFAULT_EFFECTIVE_CACHE_SIZE; Cost disable_cost = 1.0e10; -int max_parallel_degree = 0; +int max_parallel_degree = 2; bool enable_seqscan = true; bool enable_indexscan = true; diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c index 60856dda19..26ca06cfc2 100644 --- a/src/backend/utils/misc/guc.c +++ b/src/backend/utils/misc/guc.c @@ -2662,7 +2662,7 @@ static struct config_int ConfigureNamesInt[] = NULL }, &max_parallel_degree, - 0, 0, MAX_BACKENDS, + 2, 0, MAX_BACKENDS, NULL, NULL, NULL }, diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample index 14b537ffb1..f3e3de0568 100644 --- a/src/backend/utils/misc/postgresql.conf.sample +++ b/src/backend/utils/misc/postgresql.conf.sample @@ -167,7 +167,7 @@ #effective_io_concurrency = 1 # 1-1000; 0 disables prefetching #max_worker_processes = 8 -#max_parallel_degree = 0 # max number of worker processes per node +#max_parallel_degree = 2 # max number of worker processes per node #old_snapshot_threshold = -1 # 1min-60d; -1 disables; 0 is immediate # (change requires restart) #backend_flush_after = 0 # 0 disables, -- 2.40.0