From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | Thom Brown <thom(at)linux(dot)com> |
Cc: | PGSQL Mailing List <pgsql-general(at)postgresql(dot)org>, pgsql-hackers(at)postgresql(dot)org, Simon Riggs <simon(at)2ndquadrant(dot)com> |
Subject: | Re: VACUUM touching file but not updating relation |
Date: | 2011-11-18 14:47:18 |
Message-ID: | 15504.1321627638@sss.pgh.pa.us |
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Lists: | pgsql-general pgsql-hackers |
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.
regards, tom lane
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