Re: VACUUM touching file but not updating relation

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