| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Greg Stark <stark(at)mit(dot)edu> |
| Cc: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, Samrat Revagade <revagade(dot)samrat(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Patch for fail-back without fresh backup |
| Date: | 2013-06-14 14:41:31 |
| Message-ID: | 9810.1371220891@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Greg Stark <stark(at)mit(dot)edu> writes:
> On Fri, Jun 14, 2013 at 2:21 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> So it's not that we actually need to log the individual hint bit
>> changes, it's that we need to WAL-log a full page image on the first
>> update after a checkpoint, so as to recover from torn-page cases.
>> Which one are we doing?
> Wal logging a full page image after a checkpoint wouldn't actually be
> enough since subsequent hint bits will dirty the page and not wal log
> anything creating a new torn page risk. FPI are only useful if all the
> subsequent updates are wal logged.
No, there's no new torn page risk, because any crash recovery would
replay starting from the checkpoint. You might lose the
subsequently-set hint bits, but that's okay.
regards, tom lane
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