From 7711f975313e263ccde20ff045121c8add7654a1 Mon Sep 17 00:00:00 2001
From: Andres Freund <andres@anarazel.de>
Date: Mon, 25 May 2020 03:02:56 -0700
Subject: [PATCH] walwriter: Separate sleep from delay.

We should probably instead wake walwriter when wal_writer_flush_after
has passed, even if wal_writer_delay wouldn't yet trigger.

Author:
Reviewed-By:
Discussion: https://postgr.es/m/
Backpatch:
---
 src/backend/postmaster/walwriter.c |  5 +++--
 src/backend/utils/misc/guc.c       | 11 +++++++++++
 src/include/postmaster/walwriter.h |  1 +
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/backend/postmaster/walwriter.c b/src/backend/postmaster/walwriter.c
index 959004b828..5f36796fcd 100644
--- a/src/backend/postmaster/walwriter.c
+++ b/src/backend/postmaster/walwriter.c
@@ -68,6 +68,7 @@
  * GUC parameters
  */
 int			WalWriterDelay = 200;
+int			WalWriterSleep = 200;
 int			WalWriterFlushAfter = 128;
 
 /*
@@ -261,9 +262,9 @@ WalWriterMain(void)
 		 * sleep time so as to reduce the server's idle power consumption.
 		 */
 		if (left_till_hibernate > 0)
-			cur_timeout = WalWriterDelay;	/* in ms */
+			cur_timeout = WalWriterSleep;	/* in ms */
 		else
-			cur_timeout = WalWriterDelay * HIBERNATE_FACTOR;
+			cur_timeout = WalWriterSleep * HIBERNATE_FACTOR;
 
 		(void) WaitLatch(MyLatch,
 						 WL_LATCH_SET | WL_TIMEOUT | WL_EXIT_ON_PM_DEATH,
diff --git a/src/backend/utils/misc/guc.c b/src/backend/utils/misc/guc.c
index 17579eeaca..6e55fd0e5d 100644
--- a/src/backend/utils/misc/guc.c
+++ b/src/backend/utils/misc/guc.c
@@ -2752,6 +2752,17 @@ static struct config_int ConfigureNamesInt[] =
 		NULL, NULL, NULL
 	},
 
+	{
+		{"wal_writer_sleep", PGC_SIGHUP, WAL_SETTINGS,
+			gettext_noop("How often WAL writer wakes up."),
+			NULL,
+			GUC_UNIT_MS
+		},
+		&WalWriterSleep,
+		200, 1, 10000,
+		NULL, NULL, NULL
+	},
+
 	{
 		{"wal_writer_flush_after", PGC_SIGHUP, WAL_SETTINGS,
 			gettext_noop("Amount of WAL written out by WAL writer that triggers a flush."),
diff --git a/src/include/postmaster/walwriter.h b/src/include/postmaster/walwriter.h
index 3ccc332333..a24ffd008f 100644
--- a/src/include/postmaster/walwriter.h
+++ b/src/include/postmaster/walwriter.h
@@ -14,6 +14,7 @@
 
 /* GUC options */
 extern int	WalWriterDelay;
+extern int	WalWriterSleep;
 extern int	WalWriterFlushAfter;
 
 extern void WalWriterMain(void) pg_attribute_noreturn();
-- 
2.39.5