Re: Is full_page_writes=off safe in conjunction with PITR?

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Hannu Krosing <hannu(at)skype(dot)net>
Cc: pgsql-hackers(at)postgreSQL(dot)org
Subject: Re: Is full_page_writes=off safe in conjunction with PITR?
Date: 2006-04-14 21:31:22
Message-ID: 26024.1145050282@sss.pgh.pa.us
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Hannu Krosing <hannu(at)skype(dot)net> writes:
> hel kenal peval, 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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