From cd224c1524d60c9b5679a853358b59dad00a35ca Mon Sep 17 00:00:00 2001 From: Justin Pryzby Date: Sat, 3 Apr 2021 19:24:50 -0500 Subject: [PATCH 4/4] Change force_parallel_mode to a DEVELOPER GUC, and remove it from sample config.. ..to help avoid users finding this option and changing it in hopes that it'll make their queries faster, but without reading the documentation or understanding what it does. --- doc/src/sgml/config.sgml | 90 +++++++++---------- src/backend/utils/misc/guc.c | 2 +- src/backend/utils/misc/postgresql.conf.sample | 1 - 3 files changed, 46 insertions(+), 47 deletions(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index c4d5126c2a..5c7c5a39ca 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -5788,51 +5788,6 @@ SELECT * FROM parent WHERE key = 2400; - - force_parallel_mode (enum) - - force_parallel_mode configuration parameter - - - - - Allows the use of parallel queries for testing purposes even in cases - where no performance benefit is expected. - The allowed values of force_parallel_mode are - off (use parallel mode only when it is expected to improve - performance), on (force parallel query for all queries - for which it is thought to be safe), and regress (like - on, but with additional behavior changes as explained - below). - - - - More specifically, setting this value to on will add - a Gather node to the top of any query plan for which this - appears to be safe, so that the query runs inside of a parallel worker. - Even when a parallel worker is not available or cannot be used, - operations such as starting a subtransaction that would be prohibited - in a parallel query context will be prohibited unless the planner - believes that this will cause the query to fail. If failures or - unexpected results occur when this option is set, some functions used - by the query may need to be marked PARALLEL UNSAFE - (or, possibly, PARALLEL RESTRICTED). - - - - Setting this value to regress has all of the same effects - as setting it to on plus some additional effects that are - intended to facilitate automated regression testing. Normally, - messages from a parallel worker include a context line indicating that, - but a setting of regress suppresses this line so that the - output is the same as in non-parallel execution. Also, - the Gather nodes added to plans by this setting are hidden - in EXPLAIN output so that the output matches what - would be obtained if this setting were turned off. - - - - plan_cache_mode (enum) @@ -10231,6 +10186,51 @@ dynamic_library_path = 'C:\tools\postgresql;H:\my_project\lib;$libdir' + + force_parallel_mode (enum) + + force_parallel_mode configuration parameter + + + + + Allows the use of parallel queries for testing purposes even in cases + where no performance benefit is expected. + The allowed values of force_parallel_mode are + off (use parallel mode only when it is expected to improve + performance), on (force parallel query for all queries + for which it is thought to be safe), and regress (like + on, but with additional behavior changes as explained + below). + + + + More specifically, setting this value to on will add + a Gather node to the top of any query plan for which this + appears to be safe, so that the query runs inside of a parallel worker. + Even when a parallel worker is not available or cannot be used, + operations such as starting a subtransaction that would be prohibited + in a parallel query context will be prohibited unless the planner + believes that this will cause the query to fail. If failures or + unexpected results occur when this option is set, some functions used + by the query may need to be marked PARALLEL UNSAFE + (or, possibly, PARALLEL RESTRICTED). + + + + Setting this value to regress has all of the same effects + as setting it to on plus some additional effects that are + intended to facilitate automated regression testing. Normally, + messages from a parallel worker include a context line indicating that, + but a setting of regress suppresses this line so that the + output is the same as in non-parallel execution. Also, + the Gather nodes added to plans by this setting are hidden + in EXPLAIN output so that the output matches what + would be obtained if this setting were turned off. + + + + ignore_system_indexes (boolean) diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c index 27287599ad..06de7c0308 100644 --- a/src/backend/utils/misc/guc.c +++ b/src/backend/utils/misc/guc.c @@ -4840,7 +4840,7 @@ static struct config_enum ConfigureNamesEnum[] = }, { - {"force_parallel_mode", PGC_USERSET, QUERY_TUNING_OTHER, + {"force_parallel_mode", PGC_USERSET, DEVELOPER_OPTIONS, gettext_noop("Forces use of parallel query facilities."), gettext_noop("If possible, run query using a parallel worker and with parallel restrictions."), GUC_EXPLAIN diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample index 52c4373a79..50faa50462 100644 --- a/src/backend/utils/misc/postgresql.conf.sample +++ b/src/backend/utils/misc/postgresql.conf.sample @@ -415,7 +415,6 @@ #from_collapse_limit = 8 #join_collapse_limit = 8 # 1 disables collapsing of explicit # JOIN clauses -#force_parallel_mode = off #jit = on # allow JIT compilation #plan_cache_mode = auto # auto, force_generic_plan or # force_custom_plan -- 2.17.0