On Sun, Mar 16, 2025 at 06:24:59PM -0400, Robert Treat wrote: > So if the general idea is a guc "vacuum_truncate" which sets a global > default for whether vacuums and autovacuums should do truncation, and > we then have the storage parameter which would override the global > setting. And to be clear, there is also the decision on whether the > VACUUM commands default should default to truncate=on (like the > existing behavior) or truncate == vacuum_truncate guc, unless > explicitly set. I think the latter is probably the right way to go.
Thank you all for the discussion. I've attempted to address the outstanding feedback into the new version of the patch. -- nathan
>From 8d367eb19f4adf01410d5f6b96ee36f15fb345ad Mon Sep 17 00:00:00 2001 From: Nathan Bossart <nat...@postgresql.org> Date: Mon, 17 Mar 2025 10:11:56 -0500 Subject: [PATCH v4 1/1] Add vacuum_truncate configuration parameter. This new parameter works just like the eponymous storage parameter: if set to true (which is the default), autovacuum and VACUUM attempt to truncate any empty pages at the end of the table. The setting can be overridden for individual tables with the storage parameter or VACUUM's TRUNCATE option. It is primarily intended to help users avoid locking issues on hot standbys. Since there's presently no way to determine whether a Boolean storage parameter is explicitly set or has just picked up the default value, this commit introduces an optional isset_offset member to relopt_parse_elt. Suggested-by: Will Storey <w...@summercat.com> Author: Nathan Bossart <nathandboss...@gmail.com> Co-authored-by: Gurjeet Singh <gurj...@singh.im> Reviewed-by: Laurenz Albe <laurenz.a...@cybertec.at> Reviewed-by: Robert Haas <robertmh...@gmail.com> Reviewed-by: Fujii Masao <masao.fu...@oss.nttdata.com> Reviewed-by: Robert Treat <r...@xzilla.net> Discussion: https://postgr.es/m/Z2DE4lDX4tHqNGZt%40dev.null --- doc/src/sgml/config.sgml | 22 +++++++++++++++++++ doc/src/sgml/ref/create_table.sgml | 13 ++++------- doc/src/sgml/ref/vacuum.sgml | 3 ++- src/backend/access/common/reloptions.c | 14 +++++++++++- src/backend/commands/vacuum.c | 17 ++++++++++---- src/backend/utils/misc/guc_tables.c | 9 ++++++++ src/backend/utils/misc/postgresql.conf.sample | 4 ++++ src/include/access/reloptions.h | 1 + src/include/commands/vacuum.h | 1 + src/include/utils/rel.h | 1 + 10 files changed, 70 insertions(+), 15 deletions(-) diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml index 3d62c8bd274..18c11e284e4 100644 --- a/doc/src/sgml/config.sgml +++ b/doc/src/sgml/config.sgml @@ -9399,6 +9399,28 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv; </listitem> </varlistentry> + <varlistentry id="guc-vacuum-truncate" xreflabel="vacuum_truncate"> + <term><varname>vacuum_truncate</varname> (<type>boolean</type>) + <indexterm> + <primary><varname>vacuum_truncate</varname> configuration parameter</primary> + </indexterm> + </term> + <listitem> + <para> + Enables or disables vacuum to try to truncate off any empty pages at + the end of the table. The default value is <literal>true</literal>. + If <literal>true</literal>, <command>VACUUM</command> and autovacuum + do the truncation and the disk space for the truncated pages is + returned to the operating system. Note that the truncation requires + an <literal>ACCESS EXCLUSIVE</literal> lock on the table. The + <literal>TRUNCATE</literal> parameter of + <link linkend="sql-vacuum"><command>VACUUM</command></link>, if + specified, overrides the value of this parameter. The setting can be + overridden for individual tables by changing table storage parameters. + </para> + </listitem> + </varlistentry> + </variablelist> </sect2> </sect1> diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml index 5304b738322..e5c034d724e 100644 --- a/doc/src/sgml/ref/create_table.sgml +++ b/doc/src/sgml/ref/create_table.sgml @@ -1692,15 +1692,10 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM </term> <listitem> <para> - Enables or disables vacuum to try to truncate off any empty pages - at the end of this table. The default value is <literal>true</literal>. - If <literal>true</literal>, <command>VACUUM</command> and - autovacuum do the truncation and the disk space for - the truncated pages is returned to the operating system. - Note that the truncation requires <literal>ACCESS EXCLUSIVE</literal> - lock on the table. The <literal>TRUNCATE</literal> parameter - of <link linkend="sql-vacuum"><command>VACUUM</command></link>, if specified, overrides the value - of this option. + Per-table value for <xref linkend="guc-vacuum-truncate"/> parameter. The + <literal>TRUNCATE</literal> parameter of + <link linkend="sql-vacuum"><command>VACUUM</command></link>, if + specified, overrides the value of this option. </para> </listitem> </varlistentry> diff --git a/doc/src/sgml/ref/vacuum.sgml b/doc/src/sgml/ref/vacuum.sgml index 971b1237d47..bd5dcaf86a5 100644 --- a/doc/src/sgml/ref/vacuum.sgml +++ b/doc/src/sgml/ref/vacuum.sgml @@ -265,7 +265,8 @@ VACUUM [ ( <replaceable class="parameter">option</replaceable> [, ...] ) ] [ <re truncate off any empty pages at the end of the table and allow the disk space for the truncated pages to be returned to the operating system. This is normally the desired behavior - and is the default unless the <literal>vacuum_truncate</literal> + and is the default unless <xref linkend="guc-vacuum-truncate"/> + is set to false or the <literal>vacuum_truncate</literal> option has been set to false for the table to be vacuumed. Setting this option to false may be useful to avoid <literal>ACCESS EXCLUSIVE</literal> lock on the table that diff --git a/src/backend/access/common/reloptions.c b/src/backend/access/common/reloptions.c index 59fb53e7707..ccbc673b228 100644 --- a/src/backend/access/common/reloptions.c +++ b/src/backend/access/common/reloptions.c @@ -1779,6 +1779,17 @@ fillRelOptions(void *rdopts, Size basesize, char *itempos = ((char *) rdopts) + elems[j].offset; char *string_val; + /* + * If isset_offset is provided, store whether the reloption is + * set there. + */ + if (elems[j].isset_offset > 0) + { + char *setpos = ((char *) rdopts) + elems[j].isset_offset; + + *(bool *) setpos = options[i].isset; + } + switch (options[i].gen->type) { case RELOPT_TYPE_BOOL: @@ -1901,7 +1912,7 @@ default_reloptions(Datum reloptions, bool validate, relopt_kind kind) {"vacuum_index_cleanup", RELOPT_TYPE_ENUM, offsetof(StdRdOptions, vacuum_index_cleanup)}, {"vacuum_truncate", RELOPT_TYPE_BOOL, - offsetof(StdRdOptions, vacuum_truncate)}, + offsetof(StdRdOptions, vacuum_truncate), offsetof(StdRdOptions, vacuum_truncate_set)}, {"vacuum_max_eager_freeze_failure_rate", RELOPT_TYPE_REAL, offsetof(StdRdOptions, vacuum_max_eager_freeze_failure_rate)} }; @@ -1981,6 +1992,7 @@ build_local_reloptions(local_relopts *relopts, Datum options, bool validate) elems[i].optname = opt->option->name; elems[i].opttype = opt->option->type; elems[i].offset = opt->offset; + elems[i].isset_offset = 0; /* not supported for local reloptions */ i++; } diff --git a/src/backend/commands/vacuum.c b/src/backend/commands/vacuum.c index e81c9a8aba3..f0a7b87808d 100644 --- a/src/backend/commands/vacuum.c +++ b/src/backend/commands/vacuum.c @@ -78,6 +78,7 @@ int vacuum_failsafe_age; int vacuum_multixact_failsafe_age; double vacuum_max_eager_freeze_failure_rate; bool track_cost_delay_timing; +bool vacuum_truncate; /* * Variables for cost-based vacuum delay. The defaults differ between @@ -2198,13 +2199,21 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params, ((StdRdOptions *) rel->rd_options)->vacuum_max_eager_freeze_failure_rate; /* - * Set truncate option based on truncate reloption if it wasn't specified - * in VACUUM command, or when running in an autovacuum worker + * Set truncate option based on truncate reloption or GUC if it wasn't + * specified in VACUUM command, or when running in an autovacuum worker */ if (params->truncate == VACOPTVALUE_UNSPECIFIED) { - if (rel->rd_options == NULL || - ((StdRdOptions *) rel->rd_options)->vacuum_truncate) + StdRdOptions *opts = (StdRdOptions *) rel->rd_options; + + if (opts && opts->vacuum_truncate_set) + { + if (opts->vacuum_truncate) + params->truncate = VACOPTVALUE_ENABLED; + else + params->truncate = VACOPTVALUE_DISABLED; + } + else if (vacuum_truncate) params->truncate = VACOPTVALUE_ENABLED; else params->truncate = VACOPTVALUE_DISABLED; diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c index 9c0b10ad4dc..56dcda9546c 100644 --- a/src/backend/utils/misc/guc_tables.c +++ b/src/backend/utils/misc/guc_tables.c @@ -2118,6 +2118,15 @@ struct config_bool ConfigureNamesBool[] = NULL, NULL, NULL }, + { + {"vacuum_truncate", PGC_USERSET, VACUUM_AUTOVACUUM, + gettext_noop("Enables vacuum to truncate empty pages at the end of the table."), + }, + &vacuum_truncate, + true, + 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 8de86e0c945..103894f3a55 100644 --- a/src/backend/utils/misc/postgresql.conf.sample +++ b/src/backend/utils/misc/postgresql.conf.sample @@ -714,6 +714,10 @@ autovacuum_worker_slots = 16 # autovacuum worker slots to allocate #vacuum_multixact_failsafe_age = 1600000000 #vacuum_max_eager_freeze_failure_rate = 0.03 # 0 disables eager scanning +# - Default Behavior - + +#vacuum_truncate = on # enable truncation after vacuum + #------------------------------------------------------------------------------ # CLIENT CONNECTION DEFAULTS #------------------------------------------------------------------------------ diff --git a/src/include/access/reloptions.h b/src/include/access/reloptions.h index 43445cdcc6c..61e58a5daa3 100644 --- a/src/include/access/reloptions.h +++ b/src/include/access/reloptions.h @@ -152,6 +152,7 @@ typedef struct const char *optname; /* option's name */ relopt_type opttype; /* option's datatype */ int offset; /* offset of field in result struct */ + int isset_offset; /* if > 0, offset of "set" field */ } relopt_parse_elt; /* Local reloption definition */ diff --git a/src/include/commands/vacuum.h b/src/include/commands/vacuum.h index baacc63f590..bc37a80dc74 100644 --- a/src/include/commands/vacuum.h +++ b/src/include/commands/vacuum.h @@ -304,6 +304,7 @@ extern PGDLLIMPORT int vacuum_multixact_freeze_table_age; extern PGDLLIMPORT int vacuum_failsafe_age; extern PGDLLIMPORT int vacuum_multixact_failsafe_age; extern PGDLLIMPORT bool track_cost_delay_timing; +extern PGDLLIMPORT bool vacuum_truncate; /* * Relevant for vacuums implementing eager scanning. Normal vacuums may diff --git a/src/include/utils/rel.h b/src/include/utils/rel.h index db3e504c3d2..d94fddd7cef 100644 --- a/src/include/utils/rel.h +++ b/src/include/utils/rel.h @@ -344,6 +344,7 @@ typedef struct StdRdOptions int parallel_workers; /* max number of parallel workers */ StdRdOptIndexCleanup vacuum_index_cleanup; /* controls index vacuuming */ bool vacuum_truncate; /* enables vacuum to truncate a relation */ + bool vacuum_truncate_set; /* whether vacuum_truncate is set */ /* * Fraction of pages in a relation that vacuum can eagerly scan and fail -- 2.39.5 (Apple Git-154)
