From 8d085c3c939d6f60b7c6821b550f989a3f8e5a51 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Wed, 9 Jul 2025 14:19:21 -0500
Subject: [PATCH v8 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>
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 d66aa967afc..8054de78a9b 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>
@@ -75,6 +76,17 @@ CHECKPOINT [ ( option [, ...] ) ]
   <title>Parameters</title>
 
   <variablelist>
+   <varlistentry>
+    <term><literal>FLUSH_UNLOGGED</literal></term>
+    <listitem>
+     <para>
+      Normally, <command>CHECKPOINT</command> does not flush data files for
+      unlogged relations.  This option, which is disabled by default, enables
+      flushing unlogged relations.
+     </para>
+    </listitem>
+   </varlistentry>
+
    <varlistentry>
     <term><literal>MODE</literal></term>
     <listitem>
@@ -92,6 +104,20 @@ 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 723322e3e03..a3e4e70ad66 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\"", opt->defname),
 						 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..c7e6e8b16a5 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 02cdc3cbcf6..6ebcc292834 100644
--- a/src/test/regress/expected/stats.out
+++ b/src/test/regress/expected/stats.out
@@ -930,7 +930,7 @@ DROP TABLE test_stats_temp;
 -- While at it, test checkpoint options.  Note that we don't test MODE SPREAD
 -- because it would prolong the test.
 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 5ed71d7054e..dab19918056 100644
--- a/src/test/regress/sql/stats.sql
+++ b/src/test/regress/sql/stats.sql
@@ -443,7 +443,7 @@ DROP TABLE test_stats_temp;
 -- While at it, test checkpoint options.  Note that we don't test MODE SPREAD
 -- because it would prolong the test.
 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)