Add TRUNCATE parameter to VACUUM.

This commit adds new parameter to VACUUM command, TRUNCATE,
which specifies that VACUUM should attempt to 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 parameter, if specified, overrides the vacuum_truncate
reloption. If neither the reloption nor the VACUUM option is
used, the default is true, as before.

Author: Fujii Masao
Reviewed-by: Julien Rouhaud, Masahiko Sawada
Discussion: https://postgr.es/m/CAD21AoD+qtrSDL=GSma4Wd3kLYLeRC0hPna-YAdkDeV4z156vg@mail.gmail.com

doc/src/sgml/ref/create_table.sgml

@@ -1418,7 +1418,7 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       Disabling index cleanup can speed up <command>VACUUM</command> very
       significantly, but may also lead to severely bloated indexes if table
       modifications are frequent.  The <literal>INDEX_CLEANUP</literal>
-      parameter to <xref linkend="sql-vacuum"/>, if specified, overrides
+      parameter of <xref linkend="sql-vacuum"/>, if specified, overrides
       the value of this option.
      </para>
     </listitem>
@@ -1438,7 +1438,9 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
       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.
+      lock on the table. The <literal>TRUNCATE</literal> parameter
+      of <xref linkend="sql-vacuum"/>, if specified, overrides the value
+      of this option.
      </para>
     </listitem>
    </varlistentry>

doc/src/sgml/ref/vacuum.sgml

@@ -33,6 +33,7 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     DISABLE_PAGE_SKIPPING [ <replaceable class="parameter">boolean</replaceable> ]
     SKIP_LOCKED [ <replaceable class="parameter">boolean</replaceable> ]
     INDEX_CLEANUP [ <replaceable class="parameter">boolean</replaceable> ]
+    TRUNCATE [ <replaceable class="parameter">boolean</replaceable> ]
 
 <phrase>and <replaceable class="parameter">table_and_columns</replaceable> is:</phrase>
 
@@ -204,6 +205,24 @@ VACUUM [ FULL ] [ FREEZE ] [ VERBOSE ] [ ANALYZE ] [ <replaceable class="paramet
     </listitem>
    </varlistentry>
 
+   <varlistentry>
+    <term><literal>TRUNCATE</literal></term>
+    <listitem>
+     <para>
+      Specifies that <command>VACUUM</command> should attempt to
+      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>
+      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
+      the truncation requires. This option is ignored if the
+      <literal>FULL</literal> option is used.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><replaceable class="parameter">boolean</replaceable></term>
     <listitem>

src/backend/access/heap/vacuumlazy.c

@@ -163,7 +163,8 @@ static void lazy_cleanup_index(Relation indrel,
 				   LVRelStats *vacrelstats);
 static int lazy_vacuum_page(Relation onerel, BlockNumber blkno, Buffer buffer,
 				 int tupindex, LVRelStats *vacrelstats, Buffer *vmbuffer);
-static bool should_attempt_truncation(Relation rel, LVRelStats *vacrelstats);
+static bool should_attempt_truncation(VacuumParams *params,
+						 LVRelStats *vacrelstats);
 static void lazy_truncate_heap(Relation onerel, LVRelStats *vacrelstats);
 static BlockNumber count_nondeletable_pages(Relation onerel,
 						 LVRelStats *vacrelstats);
@@ -210,6 +211,7 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
 
 	Assert(params != NULL);
 	Assert(params->index_cleanup != VACOPT_TERNARY_DEFAULT);
+	Assert(params->truncate != VACOPT_TERNARY_DEFAULT);
 
 	/* not every AM requires these to be valid, but heap does */
 	Assert(TransactionIdIsNormal(onerel->rd_rel->relfrozenxid));
@@ -308,7 +310,7 @@ heap_vacuum_rel(Relation onerel, VacuumParams *params,
 	/*
 	 * Optionally truncate the relation.
 	 */
-	if (should_attempt_truncation(onerel, vacrelstats))
+	if (should_attempt_truncation(params, vacrelstats))
 		lazy_truncate_heap(onerel, vacrelstats);
 
 	/* Report that we are now doing final cleanup */
@@ -652,7 +654,7 @@ lazy_scan_heap(Relation onerel, VacuumParams *params, LVRelStats *vacrelstats,
 
 		/* see note above about forcing scanning of last page */
 #define FORCE_CHECK_PAGE() \
-		(blkno == nblocks - 1 && should_attempt_truncation(onerel, vacrelstats))
+		(blkno == nblocks - 1 && should_attempt_truncation(params, vacrelstats))
 
 		pgstat_progress_update_param(PROGRESS_VACUUM_HEAP_BLKS_SCANNED, blkno);
 
@@ -1845,12 +1847,11 @@ lazy_cleanup_index(Relation indrel,
  * careful to depend only on fields that lazy_scan_heap updates on-the-fly.
  */
 static bool
-should_attempt_truncation(Relation rel, LVRelStats *vacrelstats)
+should_attempt_truncation(VacuumParams *params, LVRelStats *vacrelstats)
 {
 	BlockNumber possibly_freeable;
 
-	if (rel->rd_options != NULL &&
+	if (params->truncate == VACOPT_TERNARY_DISABLED)
-		((StdRdOptions *) rel->rd_options)->vacuum_truncate == false)
 		return false;
 
 	possibly_freeable = vacrelstats->rel_pages - vacrelstats->nonempty_pages;

src/backend/commands/vacuum.c

@@ -98,6 +98,7 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 
 	/* Set default value */
 	params.index_cleanup = VACOPT_TERNARY_DEFAULT;
+	params.truncate = VACOPT_TERNARY_DEFAULT;
 
 	/* Parse options list */
 	foreach(lc, vacstmt->options)
@@ -126,6 +127,8 @@ ExecVacuum(ParseState *pstate, VacuumStmt *vacstmt, bool isTopLevel)
 			disable_page_skipping = defGetBoolean(opt);
 		else if (strcmp(opt->defname, "index_cleanup") == 0)
 			params.index_cleanup = get_vacopt_ternary_value(opt);
+		else if (strcmp(opt->defname, "truncate") == 0)
+			params.truncate = get_vacopt_ternary_value(opt);
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1760,6 +1763,16 @@ vacuum_rel(Oid relid, RangeVar *relation, VacuumParams *params)
 			params->index_cleanup = VACOPT_TERNARY_DISABLED;
 	}
 
+	/* Set truncate option based on reloptions if not yet */
+	if (params->truncate == VACOPT_TERNARY_DEFAULT)
+	{
+		if (onerel->rd_options == NULL ||
+			((StdRdOptions *) onerel->rd_options)->vacuum_truncate)
+			params->truncate = VACOPT_TERNARY_ENABLED;
+		else
+			params->truncate = VACOPT_TERNARY_DISABLED;
+	}
+
 	/*
 	 * Remember the relation's TOAST relation for later, if the caller asked
 	 * us to process it.  In VACUUM FULL, though, the toast table is

src/backend/postmaster/autovacuum.c

@@ -2887,6 +2887,7 @@ table_recheck_autovac(Oid relid, HTAB *table_toast_map,
 			(doanalyze ? VACOPT_ANALYZE : 0) |
 			(!wraparound ? VACOPT_SKIP_LOCKED : 0);
 		tab->at_params.index_cleanup = VACOPT_TERNARY_DEFAULT;
+		tab->at_params.truncate = VACOPT_TERNARY_DEFAULT;
 		tab->at_params.freeze_min_age = freeze_min_age;
 		tab->at_params.freeze_table_age = freeze_table_age;
 		tab->at_params.multixact_freeze_min_age = multixact_freeze_min_age;

src/bin/psql/tab-complete.c

@@ -3466,8 +3466,8 @@ psql_completion(const char *text, int start, int end)
 		if (ends_with(prev_wd, '(') || ends_with(prev_wd, ','))
 			COMPLETE_WITH("FULL", "FREEZE", "ANALYZE", "VERBOSE",
 						  "DISABLE_PAGE_SKIPPING", "SKIP_LOCKED",
-						  "INDEX_CLEANUP");
+						  "INDEX_CLEANUP", "TRUNCATE");
-		else if (TailMatches("FULL|FREEZE|ANALYZE|VERBOSE|DISABLE_PAGE_SKIPPING|SKIP_LOCKED|INDEX_CLEANUP"))
+		else if (TailMatches("FULL|FREEZE|ANALYZE|VERBOSE|DISABLE_PAGE_SKIPPING|SKIP_LOCKED|INDEX_CLEANUP|TRUNCATE"))
 			COMPLETE_WITH("ON", "OFF");
 	}
 	else if (HeadMatches("VACUUM") && TailMatches("("))

src/include/commands/vacuum.h

@@ -182,6 +182,8 @@ typedef struct VacuumParams
 									 * to use default */
 	VacOptTernaryValue index_cleanup;	/* Do index vacuum and cleanup,
 										* default value depends on reloptions */
+	VacOptTernaryValue truncate;	/* Truncate empty pages at the end,
+										* default value depends on reloptions */
 } VacuumParams;
 
 /* GUC parameters */

src/test/regress/expected/vacuum.out

@@ -88,6 +88,28 @@ VACUUM (INDEX_CLEANUP FALSE, FREEZE TRUE) vaccluster;
 -- index cleanup option is ignored if VACUUM FULL
 VACUUM (INDEX_CLEANUP TRUE, FULL TRUE) no_index_cleanup;
 VACUUM (FULL TRUE) no_index_cleanup;
+-- TRUNCATE option
+CREATE TABLE vac_truncate_test(i INT NOT NULL, j text)
+	WITH (vacuum_truncate=true, autovacuum_enabled=false);
+INSERT INTO vac_truncate_test VALUES (1, NULL), (NULL, NULL);
+ERROR:  null value in column "i" violates not-null constraint
+DETAIL:  Failing row contains (null, null).
+VACUUM (TRUNCATE FALSE) vac_truncate_test;
+SELECT pg_relation_size('vac_truncate_test') > 0;
+ ?column? 
+----------
+ t
+(1 row)
+
+VACUUM vac_truncate_test;
+SELECT pg_relation_size('vac_truncate_test') = 0;
+ ?column? 
+----------
+ t
+(1 row)
+
+VACUUM (TRUNCATE FALSE, FULL TRUE) vac_truncate_test;
+DROP TABLE vac_truncate_test;
 -- partitioned table
 CREATE TABLE vacparted (a int, b char) PARTITION BY LIST (a);
 CREATE TABLE vacparted1 PARTITION OF vacparted FOR VALUES IN (1);

src/test/regress/sql/vacuum.sql

@@ -71,6 +71,17 @@ VACUUM (INDEX_CLEANUP FALSE, FREEZE TRUE) vaccluster;
 VACUUM (INDEX_CLEANUP TRUE, FULL TRUE) no_index_cleanup;
 VACUUM (FULL TRUE) no_index_cleanup;
 
+-- TRUNCATE option
+CREATE TABLE vac_truncate_test(i INT NOT NULL, j text)
+	WITH (vacuum_truncate=true, autovacuum_enabled=false);
+INSERT INTO vac_truncate_test VALUES (1, NULL), (NULL, NULL);
+VACUUM (TRUNCATE FALSE) vac_truncate_test;
+SELECT pg_relation_size('vac_truncate_test') > 0;
+VACUUM vac_truncate_test;
+SELECT pg_relation_size('vac_truncate_test') = 0;
+VACUUM (TRUNCATE FALSE, FULL TRUE) vac_truncate_test;
+DROP TABLE vac_truncate_test;
+
 -- partitioned table
 CREATE TABLE vacparted (a int, b char) PARTITION BY LIST (a);
 CREATE TABLE vacparted1 PARTITION OF vacparted FOR VALUES IN (1);