Re: BUG #10675: alter database set tablespace and unlogged table

On 2014-07-02 11:38:51 -0400, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > I think one reason for the separate flag is that the checkpoint
> > performed by pg_start_backup/pg_basebackup shouldn't just become more
> > expensive because unlogged tables are needlessly flushed to disk. After
> > all, unlogged tables are used because normal tables have a too high
> > overhead in that scenario.
>
> AFAIK, the "overhead" that unlogged tables are trying to avoid is WAL
> I/O. Nobody has argued (until this thread) that we are worried about
> whether checkpoints write them.

I don't think that's true. In production scenarios checkpoint IO is one
of the two top problems I see (the other being crazy amount of WAL due
to FPIs because of too short checkpoints). And unlogged tables have
explicitly been excluded from checkpoints, so it's not like nobody has
thought about it. I seem to recall lengthy discussions even. Yep
the discussion is around
http://archives.postgresql.org/message-id/AANLkTimxC%2BG9M9_s0dXa_huoAeZpkCmoWCo5S-7DsLi%3D%40mail.gmail.com

Greetings,

Andres Freund

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Andres Freund http://www.2ndQuadrant.com/
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