From: | Simon Riggs <simon(at)2ndQuadrant(dot)com> |
---|---|
To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Thom Brown <thom(at)linux(dot)com>, PGSQL Mailing List <pgsql-general(at)postgresql(dot)org>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: VACUUM touching file but not updating relation |
Date: | 2011-11-18 14:55:49 |
Message-ID: | CA+U5nMK18PCNhjO==MxpyZn278F+QM_O5fMwhCuxicx5fu=asw@mail.gmail.com |
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On Fri, Nov 18, 2011 at 2:47 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> Thom Brown <thom(at)linux(dot)com> writes:
>>> On 11 November 2011 23:28, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>>>> I observe that _bt_delitems_vacuum() unconditionally dirties the page
>>>> and writes a WAL record, whether it has anything to do or not; and that
>>>> if XLogStandbyInfoActive() then btvacuumscan will indeed call it despite
>>>> there being (probably) nothing useful to do. Seems like that could be
>>>> improved. The comment explaining why it's necessary to do that doesn't
>>>> make any sense to me, either.
>
>>> Well the effect, in the single instances I've checked, is certainly
>>> more pronounced for hot_standby, but there still appears to be some
>>> occurrences for minimal wal_level too.
>
>> So would you say this is acceptable and normal activity, or is
>> something awry here?
>
> Well, it's expected given the current coding in the btree vacuum logic.
> It's not clear to me why it was written like that, though.
I'll take a look.
--
Simon Riggs http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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