Re: checkpoint_segments upgrade recommendation?

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От Michael Paquier
Тема Re: checkpoint_segments upgrade recommendation?
Дата
Msg-id CAB7nPqRM5eRU0EKntVd6M6emM+t=UsvyynzrX2TQiTEQPw23Eg@mail.gmail.com
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Ответ на Re: checkpoint_segments upgrade recommendation?  (Robert Haas <robertmhaas@gmail.com>)
Ответы Re: checkpoint_segments upgrade recommendation?
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On Sat, Oct 17, 2015 at 4:45 AM, Robert Haas <robertmhaas@gmail.com> wrote:
On Fri, Oct 16, 2015 at 2:52 PM, Peter Eisentraut <peter_e@gmx.net> wrote:
> The release notes say that checkpoint_segments has been replaced by
> max_wal_size and min_wal_size, but there is no indication on how to
> convert between the old and new settings.  I think a lot of people will
> have checkpoint_segments delicately tuned, so we should at least give
> them a hint on how to carry that forward in spirit.

Yeah, it would be nice to have some guidance about that.  But do we
know what the guidance should be?

I think that we should just suggest a reverse formula of the maximum soft limit of checkpoint_segments for max_wal_size in the release notes of 9.5, basically:
(3 * your_old_checkpoint_segments + 1) * 16MB = max_wal_size
I am not sure it is worth mentioning that one needs to be be sure to keep some extra room to handle potential spikes because that's not a hard limit, but people who have already played with pg_xlog on a different partition are already aware of that after tuning checkpoint_segments.
min_wal_size is a new parameter though, I don't think it matters much to hint users for the transfer to the new configuration...
Regards,
--
Michael

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