Date: Fri, 2 Oct 2015 11:58:39 -0300
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: oonishitk@nttdata.co.jp, pgsql-docs <pgsql-docs@postgresql.org>,
 PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: max_worker_processes on the standby
Message-ID: <20151002145839.GZ2573@alvherre.pgsql>
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Fujii Masao wrote:

> What happens if pg_xact_commit_timestamp() is called in standby after
> track_commit_timestamp is disabled in master, DeactivateCommitTs() is
> called and all commit_ts files are removed in standby? I tried that case
> and got the following assertion failure.

Ah.  So the standby needs to keep the module activated if it's enabled
locally, even when it receives a message that the master turned it off.
Here's a patch.

Thanks for your continued testing!

-- 
Álvaro Herrera                http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

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commit 7441f88b746b7522f1714ed9fec95c3c4fe1dacb=1B[m
Author:     Alvaro Herrera <alvherre@alvh.no-ip.org>
AuthorDate: Fri Oct 2 11:39:44 2015 -0300
CommitDate: Fri Oct 2 11:39:44 2015 -0300

    Don't disable commit_ts in standby if enabled locally
=20=20=20=20
    Bug noticed by Fujii Masao

diff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/tr=
ansam/commit_ts.c
index 79ca04a..24b8291 100644
--- a/src/backend/access/transam/commit_ts.c
+++ b/src/backend/access/transam/commit_ts.c
@@ -583,14 +583,15 @@ CommitTsParameterChange(bool newvalue, bool oldvalue)
 	 * pg_control.  If the old value was already set, we already did this, so
 	 * don't do anything.
 	 *
-	 * If the module is disabled in the master, disable it here too.
+	 * If the module is disabled in the master, disable it here too, unless
+	 * the module is enabled locally.
 	 */
 	if (newvalue)
 	{
 		if (!track_commit_timestamp && !oldvalue)
 			ActivateCommitTs();
 	}
-	else if (oldvalue)
+	else if (!track_commit_timestamp && oldvalue)
 		DeactivateCommitTs(false);
 }
=20

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