From 0269d61a12e604bc7679d8724e0924a4be2e2cc1 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Thu, 10 Jul 2025 10:47:55 -0500
Subject: [PATCH v9 5/5] Add FLUSH_UNLOGGED option to CHECKPOINT command.

This option, which is disabled by default, can be used to request
the checkpoint also flush data files for unlogged relations.  As
with the MODE option, the server may consolidate the options for
concurrently requested checkpoints.  For example, if one session
uses (FLUSH_UNLOGGED FALSE) and another uses (FLUSH_UNLOGGED TRUE),
the server may perform one checkpoint with FLUSH_UNLOGGED enabled.

Author: Christoph Berg <myon@debian.org>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Reviewed-by: Fujii Masao <masao.fujii@oss.nttdata.com>
Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com>
Discussion: https://postgr.es/m/aDnaKTEf-0dLiEfz%40msg.df7cb.de
---
 doc/src/sgml/ref/checkpoint.sgml      | 26 ++++++++++++++++++++++++++
 src/backend/postmaster/checkpointer.c |  4 ++++
 src/bin/psql/tab-complete.in.c        |  2 +-
 src/test/regress/expected/stats.out   |  2 +-
 src/test/regress/sql/stats.sql        |  2 +-
 5 files changed, 33 insertions(+), 3 deletions(-)

diff --git a/doc/src/sgml/ref/checkpoint.sgml b/doc/src/sgml/ref/checkpoint.sgml
index 36a9e323f44..cd981cf2cab 100644
--- a/doc/src/sgml/ref/checkpoint.sgml
+++ b/doc/src/sgml/ref/checkpoint.sgml
@@ -25,6 +25,7 @@ CHECKPOINT [ ( option [, ...] ) ]
 
 <phrase>where <replaceable class="parameter">option</replaceable> can be one of:</phrase>
 
+    FLUSH_UNLOGGED [ <replaceable class="parameter">boolean</replaceable> ]
     MODE { FAST | SPREAD }
 </synopsis>
  </refsynopsisdiv>
@@ -76,6 +77,17 @@ CHECKPOINT [ ( option [, ...] ) ]
   <title>Parameters</title>
 
   <variablelist>
+   <varlistentry>
+    <term><literal>FLUSH_UNLOGGED</literal></term>
+    <listitem>
+     <para>
+      Normally, <command>CHECKPOINT</command> does not flush dirty buffers of
+      unlogged relations.  This option, which is disabled by default, enables
+      flushing unlogged relations to disk.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>MODE</literal></term>
     <listitem>
@@ -93,6 +105,20 @@ CHECKPOINT [ ( option [, ...] ) ]
      </para>
     </listitem>
    </varlistentry>
+
+   <varlistentry>
+    <term><replaceable class="parameter">boolean</replaceable></term>
+    <listitem>
+     <para>
+      Specifies whether the selected option should be turned on or off.
+      You can write <literal>TRUE</literal>, <literal>ON</literal>, or
+      <literal>1</literal> to enable the option, and <literal>FALSE</literal>,
+      <literal>OFF</literal>, or <literal>0</literal> to disable it.  The
+      <replaceable class="parameter">boolean</replaceable> value can also
+      be omitted, in which case <literal>TRUE</literal> is assumed.
+     </para>
+    </listitem>
+   </varlistentry>
   </variablelist>
  </refsect1>
 
diff --git a/src/backend/postmaster/checkpointer.c b/src/backend/postmaster/checkpointer.c
index 9d77269a374..2809e298a44 100644
--- a/src/backend/postmaster/checkpointer.c
+++ b/src/backend/postmaster/checkpointer.c
@@ -989,6 +989,7 @@ void
 ExecCheckpoint(ParseState *pstate, CheckPointStmt *stmt)
 {
 	bool		fast = true;
+	bool		unlogged = false;
 
 	foreach_ptr(DefElem, opt, stmt->options)
 	{
@@ -1004,6 +1005,8 @@ ExecCheckpoint(ParseState *pstate, CheckPointStmt *stmt)
 						 errmsg("unrecognized MODE option \"%s\"", mode),
 						 parser_errposition(pstate, opt->location)));
 		}
+		else if (strcmp(opt->defname, "flush_unlogged") == 0)
+			unlogged = defGetBoolean(opt);
 		else
 			ereport(ERROR,
 					(errcode(ERRCODE_SYNTAX_ERROR),
@@ -1022,6 +1025,7 @@ ExecCheckpoint(ParseState *pstate, CheckPointStmt *stmt)
 
 	RequestCheckpoint(CHECKPOINT_WAIT |
 					  (fast ? CHECKPOINT_FAST : 0) |
+					  (unlogged ? CHECKPOINT_FLUSH_UNLOGGED : 0) |
 					  (RecoveryInProgress() ? 0 : CHECKPOINT_FORCE));
 }
 
diff --git a/src/bin/psql/tab-complete.in.c b/src/bin/psql/tab-complete.in.c
index a7db04efd93..6872653c6c8 100644
--- a/src/bin/psql/tab-complete.in.c
+++ b/src/bin/psql/tab-complete.in.c
@@ -3165,7 +3165,7 @@ match_previous_words(int pattern_id,
 		 * one word, so the above test is correct.
 		 */
 		if (ends_with(prev_wd, '(') || ends_with(prev_wd, ','))
-			COMPLETE_WITH("MODE");
+			COMPLETE_WITH("MODE", "FLUSH_UNLOGGED");
 		else if (TailMatches("MODE"))
 			COMPLETE_WITH("FAST", "SPREAD");
 	}
diff --git a/src/test/regress/expected/stats.out b/src/test/regress/expected/stats.out
index b4df9ad5960..b9dd5317163 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -938,7 +938,7 @@ ERROR:  unrecognized MODE option "wrong"
 LINE 1: CHECKPOINT (MODE WRONG);
                     ^
 CHECKPOINT (MODE FAST);
-CHECKPOINT;
+CHECKPOINT (FLUSH_UNLOGGED);
 SELECT num_requested > :rqst_ckpts_before FROM pg_stat_checkpointer;
  ?column? 
 ----------
diff --git a/src/test/regress/sql/stats.sql b/src/test/regress/sql/stats.sql
index 0868b250a64..3c6837c5c94 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -445,7 +445,7 @@ DROP TABLE test_stats_temp;
 CHECKPOINT (WRONG);
 CHECKPOINT (MODE WRONG);
 CHECKPOINT (MODE FAST);
-CHECKPOINT;
+CHECKPOINT (FLUSH_UNLOGGED);
 
 SELECT num_requested > :rqst_ckpts_before FROM pg_stat_checkpointer;
 SELECT wal_bytes > :wal_bytes_before FROM pg_stat_wal;
-- 
2.39.5 (Apple Git-154)