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Add vacuum_truncate configuration parameter.

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This new parameter works just like the storage parameter of the
same name: if set to true (which is the default), autovacuum and
VACUUM attempt to truncate any empty pages at the end of the table.
It is primarily intended to help users avoid locking issues on hot
standbys.  The setting can be overridden with the storage parameter
or VACUUM's TRUNCATE option.

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 also introduces an isset_offset member
to relopt_parse_elt.

Suggested-by: Will Storey <will@summercat.com>
Author: Nathan Bossart <nathandbossart@gmail.com>
Co-authored-by: Gurjeet Singh <gurjeet@singh.im>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Reviewed-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Reviewed-by: Robert Treat <rob@xzilla.net>
Discussion: https://postgr.es/m/Z2DE4lDX4tHqNGZt%40dev.null
This commit is contained in:
Nathan Bossart 2025-03-20 10:16:50 -05:00
parent 618c64ffd3
commit 0164a0f9ee
13 changed files with 116 additions and 15 deletions
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29
doc/src/sgml/config.sgml
View File

@ -9311,6 +9311,35 @@ COPY postgres_log FROM '/full/path/to/logfile.csv' WITH csv;
</note>
</sect2>
<sect2 id="runtime-config-vacuum-default">
<title>Default Behavior</title>
<variablelist>
<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
also be overridden for individual tables by changing table storage
parameters.
</para>
</listitem>
</varlistentry>
</variablelist>
</sect2>
<sect2 id="runtime-config-vacuum-freezing">
<title>Freezing</title>

13
doc/src/sgml/ref/create_table.sgml
View File

@ -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>

3
doc/src/sgml/ref/vacuum.sgml
View File

@ -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

14
src/backend/access/common/reloptions.c
View File

@ -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 relopts yet */
i++;
}

17
src/backend/commands/vacuum.c
View File

@ -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;

10
src/backend/utils/misc/guc_tables.c
View File

@ -712,6 +712,7 @@ const char *const config_group_names[] =
[STATS_CUMULATIVE] = gettext_noop("Statistics / Cumulative Query and Index Statistics"),
[VACUUM_AUTOVACUUM] = gettext_noop("Vacuuming / Automatic Vacuuming"),
[VACUUM_COST_DELAY] = gettext_noop("Vacuuming / Cost-Based Vacuum Delay"),
[VACUUM_DEFAULT] = gettext_noop("Vacuuming / Default Behavior"),
[VACUUM_FREEZING] = gettext_noop("Vacuuming / Freezing"),
[CLIENT_CONN_STATEMENT] = gettext_noop("Client Connection Defaults / Statement Behavior"),
[CLIENT_CONN_LOCALE] = gettext_noop("Client Connection Defaults / Locale and Formatting"),
@ -2131,6 +2132,15 @@ struct config_bool ConfigureNamesBool[] =
NULL, NULL, NULL
},
{
{"vacuum_truncate", PGC_USERSET, VACUUM_DEFAULT,
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

4
src/backend/utils/misc/postgresql.conf.sample
View File

@ -714,6 +714,10 @@ autovacuum_worker_slots = 16 # autovacuum worker slots to allocate
#vacuum_cost_page_dirty = 20 # 0-10000 credits
#vacuum_cost_limit = 200 # 1-10000 credits
# - Default Behavior -
#vacuum_truncate = on # enable truncation after vacuum
# - Freezing -
#vacuum_freeze_table_age = 150000000

1
src/include/access/reloptions.h
View File

@ -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 "is set" field */
} relopt_parse_elt;
/* Local reloption definition */

1
src/include/commands/vacuum.h
View File

@ -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

1
src/include/utils/guc_tables.h
View File

@ -89,6 +89,7 @@ enum config_group
STATS_CUMULATIVE,
VACUUM_AUTOVACUUM,
VACUUM_COST_DELAY,
VACUUM_DEFAULT,
VACUUM_FREEZING,
CLIENT_CONN_STATEMENT,
CLIENT_CONN_LOCALE,

1
src/include/utils/rel.h
View File

@ -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

27
src/test/regress/expected/vacuum.out
View File

@ -236,6 +236,7 @@ SELECT pg_relation_size('vac_truncate_test') > 0;
t
(1 row)
SET vacuum_truncate = false;
VACUUM (DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') = 0;
?column?
@ -244,6 +245,32 @@ SELECT pg_relation_size('vac_truncate_test') = 0;
(1 row)
VACUUM (TRUNCATE FALSE, FULL TRUE) vac_truncate_test;
ALTER TABLE vac_truncate_test RESET (vacuum_truncate);
INSERT INTO vac_truncate_test VALUES (1, NULL), (NULL, NULL);
ERROR: null value in column "i" of relation "vac_truncate_test" violates not-null constraint
DETAIL: Failing row contains (null, null).
VACUUM (DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') > 0;
?column?
----------
t
(1 row)
RESET vacuum_truncate;
VACUUM (TRUNCATE FALSE, DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') > 0;
?column?
----------
t
(1 row)
VACUUM (DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') = 0;
?column?
----------
t
(1 row)
DROP TABLE vac_truncate_test;
-- partitioned table
CREATE TABLE vacparted (a int, b char) PARTITION BY LIST (a);

10
src/test/regress/sql/vacuum.sql
View File

@ -194,9 +194,19 @@ CREATE TEMP TABLE vac_truncate_test(i INT NOT NULL, j text)
INSERT INTO vac_truncate_test VALUES (1, NULL), (NULL, NULL);
VACUUM (TRUNCATE FALSE, DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') > 0;
SET vacuum_truncate = false;
VACUUM (DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') = 0;
VACUUM (TRUNCATE FALSE, FULL TRUE) vac_truncate_test;
ALTER TABLE vac_truncate_test RESET (vacuum_truncate);
INSERT INTO vac_truncate_test VALUES (1, NULL), (NULL, NULL);
VACUUM (DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') > 0;
RESET vacuum_truncate;
VACUUM (TRUNCATE FALSE, DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') > 0;
VACUUM (DISABLE_PAGE_SKIPPING) vac_truncate_test;
SELECT pg_relation_size('vac_truncate_test') = 0;
DROP TABLE vac_truncate_test;
-- partitioned table