From: | Heikki Linnakangas <hlinnakangas(at)vmware(dot)com> |
---|---|
To: | Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com> |
Cc: | Andres Freund <andres(at)2ndquadrant(dot)com>, Sawada Masahiko <sawada(dot)mshk(at)gmail(dot)com>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Samrat Revagade <revagade(dot)samrat(at)gmail(dot)com>, Peter Eisentraut <peter_e(at)gmx(dot)net>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: Patch for fail-back without fresh backup |
Date: | 2013-10-08 15:52:04 |
Message-ID: | 52542A24.9010706@vmware.com |
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Lists: | pgsql-hackers |
On 08.10.2013 13:00, Pavan Deolasee wrote:
> On Tue, Oct 8, 2013 at 3:16 PM, Andres Freund<andres(at)2ndquadrant(dot)com>wrote:
>
>> It is my impression that there still are several people having pretty
>> fundamental doubts about this approach in general. From what I remember
>> neither Heikki, Simon, Tom nor me were really convinced about this
>> approach.
>>
> IIRC you and Tom were particularly skeptical about the approach. But do you
> see a technical flaw or a show stopper with the approach ? Heikki has
> written pg_rewind which is really very cool. But it fails to handle the
> hint bit updates which are not WAL logged unless of course checksums are
> turned on. We can have a GUC controlled option to turn WAL logging on for
> hint bit updates and then use pg_rewind for the purpose. But I did not see
> any agreement on that either. Performance implication of WAL logging every
> hint bit update could be huge.
Yeah, I definitely think we should work on the pg_rewind approach
instead of this patch. It's a lot more flexible. The performance hit of
WAL-logging hint bit updates is the price you have to pay, but a lot of
people were OK with that to get page checksum, so I think a lot of
people would be OK with it for this purpose too. As long as it's
optional, of course. And anyone using page checksums are already paying
that price.
- Heikki
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