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Re: Clean shutdown and warm standby

From: Andreas Pflug <pgadmin(at)pse-consulting(dot)de>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Guillaume Smet <guillaume(dot)smet(at)gmail(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Clean shutdown and warm standby
Date: 2009-04-27 21:43:17
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Heikki Linnakangas wrote:
> No, no crash is involved. Just a normal server shutdown and start:
> 1. Server shutdown is initiated
> 2. A shutdown checkpoint is recorded at XLOG point 1234, redo ptr is 
> also 1234.
> 3. A XLOG_SWITCH record is written at 1235, right after the checkpoint 
> record.
> 4. The last round of archiving is done. The partial WAL file 
> containing the checkpoint and XLOG_SWITCH record is archived.
> 5. Postmaster exits.
> 6. Postmaster is started again. Since the system was shut down 
> cleanly, no WAL recovery is done. The WAL insert pointer is 
> initialized to right after the redo pointer, location 1235, which is 
> also the location of the XLOG_SWITCH record.
> 7. The next WAL record written will be written at 1235, overwriting 
> the XLOG_SWITCH record.
> 8. When the WAL file fills up, the system will try to archive the same 
> WAL file again, this time with additional WAL records that after the 
> checkpoint record. 

So to get this down to a solution, it appears to be correct to execute 
the RequestXLogSwitch right before CreateCheckPoint?


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