From: Petr Jelinek <petr@2ndquadrant.com>
To: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Fujii Masao <masao.fujii@gmail.com>
Cc: Robert Haas <robertmhaas@gmail.com>
Cc: oonishitk@nttdata.co.jp, pgsql-docs <pgsql-docs@postgresql.org>
Cc: PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: [DOCS] max_worker_processes on the standby
Date: Thu, 3 Dec 2015 17:19:53 +0100
Message-ID: <56606BA9.1050606@2ndquadrant.com> (raw)
In-Reply-To: <20151116214338.GD614468@alvherre.pgsql>
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On 2015-11-16 22:43, Alvaro Herrera wrote:
> I paraphrase Fujii Masao, who wrote:
>
>> 1. Start the master and standby servers with track_commit_timestamp enabled.
>> 2. Disable track_commit_timestamp in the master and restart the master server.
>> 3. Run checkpoint in the master.
>> 4. Run restartpoint in the standby after the checkpoint WAL record generated
>> 5. Restart the standby server.
>> 6. Enable track_commit_timestamp in the master and restart the master server.
>> 7. Disable track_commit_timestamp in the master and restart the master server.
>
>> What I think strange is that pg_last_committed_xact() behaves differently
>> in #2, #5, and #7 though the settings of track_commit_timestamp are same
>> in both servers, i.e., it's disabled in the master but enabled in the standby.
>
> Interesting, thanks. You're right that this behaves oddly.
>
> I think in order to fix these two points (#5 and #7), we need to make
> the standby not honour the GUC at all, i.e. only heed what the master
> setting is.
>
>> 8. Promote the standby server to new master.
>> Since committs is still inactive even after the promotion,
>> pg_last_committed_xact() keeps causing an ERROR though
>> track_commit_timestamp is on.
>>
>> I was thinking that whether committs is active or not should depend on
>> the setting of track_commit_timestamp *after* the promotion.
>> The behavior in #8 looked strange.
>
> To fix this problem, we can re-run StartupCommitTs() after recovery is
> done, this time making sure to honour the GUC setting.
>
> I haven't tried the scenarios we fixed with the previous round of
> patching, but this patch seems to close the problems just reported.
> (My next step will be looking over the recovery test framework by
> Michael et al, so that I can apply a few tests for this stuff.)
> In the meantime, if you can look this over I would appreciate it.
>
While this seems good, I'd code it slightly differently. I didn't like
the addition of new bool when it's not really needed. This brings the
question if we actually need the BootStrapCommitTs and StartupCommitTs
functions which really don't do much though.
--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackersAttachments:committs-activation-fix.patch (binary/octet-stream, 1.8K) downloaddiff --git a/src/backend/access/transam/commit_ts.c b/src/backend/access/transam/commit_ts.cindex 349228d..edb0d2b 100644--- a/src/backend/access/transam/commit_ts.c+++ b/src/backend/access/transam/commit_ts.c@@ -510,7 +510,7 @@ BootStrapCommitTs(void)
/*
* Nothing to do here at present, unlike most other SLRU modules; segments
* are created when the server is started with this module enabled. See
- * StartupCommitTs.+ * ActivateCommitTs.
*/
}
@@ -544,13 +544,13 @@ ZeroCommitTsPage(int pageno, bool writeXlog)
* configuration.
*/
void
-StartupCommitTs(bool force_enable)+StartupCommitTs(bool enabled)
{
/*
* If the module is not enabled, there's nothing to do here. The module
* could still be activated from elsewhere.
*/
- if (track_commit_timestamp || force_enable)+ if (enabled)
ActivateCommitTs();
}
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.cindex f17f834..ee0b959 100644--- a/src/backend/access/transam/xlog.c+++ b/src/backend/access/transam/xlog.c@@ -7339,7 +7339,7 @@ StartupXLOG(void)
if (standbyState == STANDBY_DISABLED)
{
StartupCLOG();
- StartupCommitTs(false);+ StartupCommitTs(track_commit_timestamp);
StartupSUBTRANS(oldestActiveXID);
}
diff --git a/src/include/access/commit_ts.h b/src/include/access/commit_ts.hindex 3844bb3..f5b3969 100644--- a/src/include/access/commit_ts.h+++ b/src/include/access/commit_ts.h@@ -34,7 +34,7 @@ extern Size CommitTsShmemBuffers(void);
extern Size CommitTsShmemSize(void);
extern void CommitTsShmemInit(void);
extern void BootStrapCommitTs(void);
-extern void StartupCommitTs(bool force_enable);+extern void StartupCommitTs(bool enabled);
extern void CommitTsParameterChange(bool xlrecvalue, bool pgcontrolvalue);
extern void CompleteCommitTsInitialization(void);
extern void ShutdownCommitTs(void);
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Cc: petr@2ndquadrant.com, alvherre@2ndquadrant.com, masao.fujii@gmail.com, robertmhaas@gmail.com, pgsql-docs@postgresql.org
Subject: Re: [DOCS] max_worker_processes on the standby
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