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Re: Streaming replication and pg_xlogfile_name()

From: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
To: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Streaming replication and pg_xlogfile_name()
Date: 2010-02-22 12:30:19
Message-ID: 4B8278DB.5000206@enterprisedb.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Fujii Masao wrote:
> On Thu, Jan 28, 2010 at 5:28 PM, Heikki Linnakangas
> <heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>> How about extending the format of the string returned by
>> pg_last_xlog_receive/replay_location() to include the timeline ID? When
>> it currently returns e.g '6/200016C', it could return '1/6/200016C',
>> where 1 is the timeline ID. Then just teach pg_xlogfile_name[_offset]()
>> to accept that format as well.
> 
> Sounds good. The attached patch does so. Also the code is available
> in the 'replication' branch in my git repository.

> --- 5866,5882 ----
>   			/* use volatile pointer to prevent code rearrangement */
>   			volatile XLogCtlData *xlogctl = XLogCtl;
>   
> ! 			/*
> ! 			 * initialize shared replayEndRecPtr, recoveryLastRecPtr and
> ! 			 * recoveryLastTLI. Actually, the latter two variables don't need to
> ! 			 * be initialized here since they are expected to be updated at least
> ! 			 * once until read only connections will have read them. But just in
> ! 			 * case.
> ! 			 */
>   			SpinLockAcquire(&xlogctl->info_lck);
>   			xlogctl->replayEndRecPtr = ReadRecPtr;
>   			xlogctl->recoveryLastRecPtr = ReadRecPtr;
> + 			xlogctl->recoveryLastTLI = curFileTLI;
>   			SpinLockRelease(&xlogctl->info_lck);
>   
>   			InRedo = true;

Thinking about this again, I'm not sure this is a good idea. Using
curFileTLI makes sense if you're going to call pg_xlogfile_name() and
would expect it to return the filename of the file containing the WAL
record being replayed. But in other contexts, it seems strange for
pg_last_replay_timeline() to return the TLI of the first record in the
file, rather than the actual record replayed.

I don't have any better ideas, though.

-- 
  Heikki Linnakangas
  EnterpriseDB   http://www.enterprisedb.com

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