|From:||Andres Freund <andres(at)anarazel(dot)de>|
|To:||Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>|
|Cc:||"David G(dot) Johnston" <david(dot)g(dot)johnston(at)gmail(dot)com>, Hadi Moshayedi <hadi(at)citusdata(dot)com>, Postgres General <pgsql-general(at)postgresql(dot)org>|
|Subject:||Re: index-only-scan when there is an index on all columns|
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On 2018-02-27 16:58:11 -0500, Tom Lane wrote:
> > Also, I recall discussion that select statements will touch the visibility
> > map (hence causing write I/O even in a read-only query) but  indicates
> > that only vacuum will set them ddl will clear them.
> Hm, I don't recall that, but I've not been involved in the last few rounds
> of hacking on that mechanism.
I'm fairly certain that only vacuum and table rewrites like cluster sets
all-visible, and that there was never any released code that did so
during SELECT. I think there were a few patches debating whether we
could change that, but they never really got anywhere afair.
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