Re: [9.4] Make full_page_writes only settable on server start?
От | Jeff Davis |
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Тема | Re: [9.4] Make full_page_writes only settable on server start? |
Дата | |
Msg-id | 1378309777.23979.39.camel@jdavis обсуждение исходный текст |
Ответ на | Re: [9.4] Make full_page_writes only settable on server start? (Andres Freund <andres@2ndquadrant.com>) |
Список | pgsql-hackers |
On Wed, 2013-09-04 at 17:00 +0200, Andres Freund wrote: > On 2013-09-04 07:57:15 -0700, Jeff Davis wrote: > > XLogSaveBufferForHint() calls XLogCheckBuffer() but doesn't also look at > > the full page writes setting (like in XLogInsert()). That means, if > > checksums are enabled and full_page_writes is off, we'll still write > > some full page images for checksums. I'd like to remedy that. > > I don't think that's really as easy as it sounds without removing the > ability to do base backups with full_page_writes = off. The interlocking > that would require makes things complex... I didn't dig into that part yet. I was mostly distracted by the code to support changing full_page_writes with SIGHUP. One option would be to have XLogInsert return early if full_page_writes is off, it's an XLOG_FPI record, and forcePageWrites is off. > Personally I'd rather forbid enabling checkpoints in the combination > with full_page_writes = off. That doesn't seem like a good idea to me > and I am far from convinced it's actually going to work in all corner cases. Hmm. It's good to be cautious when deploying on a less-common configuration. However, I don't think it's a good idea to reject seemingly valid combinations that are supposed to work due to a lack of confidence in the review/testing process. Might be an area warranting some further review and testing; I'll take a look, but feel free to tell me if you can think of specific problem areas. Regards,Jeff Davis
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