Re: Is full_page_writes=off safe in conjunction with PITR? - Mailing list pgsql-hackers

From Tom Lane
Subject Re: Is full_page_writes=off safe in conjunction with PITR?
Date
Msg-id 26024.1145050282@sss.pgh.pa.us
Whole thread Raw
In response to Re: Is full_page_writes=off safe in conjunction with  (Hannu Krosing <hannu@skype.net>)
Responses Re: Is full_page_writes=off safe in conjunction with  (Hannu Krosing <hannu@skype.net>)
Re: Is full_page_writes=off safe in conjunction with PITR?  (Bruce Momjian <pgman@candle.pha.pa.us>)
List pgsql-hackers
Hannu Krosing <hannu@skype.net> writes:
> Ühel kenal päeval, R, 2006-04-14 kell 16:40, kirjutas Tom Lane:
>> If the backup-taker reads, say, 4K at a time then it's
>> certainly possible that it gets a later version of the second half of a
>> page than it got of the first half.  I don't know about you, but I sure
>> don't feel comfortable making assumptions at that level about the
>> behavior of tar or cpio.
>> 
>> I fear we still have to disable full_page_writes (force it ON) if
>> XLogArchivingActive is on.  Comments?

> Why not just tell the backup-taker to take backups using 8K pages ? 

How?  (No, I don't think tar's blocksize options control this
necessarily --- those indicate the blocking factor on the *tape*.
And not everyone uses tar anyway.)

Even if this would work for all popular backup programs, it seems
far too fragile: the consequence of forgetting the switch would be
silent data corruption, which you might not notice until the slave
had been in live operation for some time.
        regards, tom lane


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