Re: Let's drop two obsolete features which are bear-traps for novices

On 2014-11-01 14:48:20 -0400, Tom Lane wrote:
> Andres Freund <andres(at)2ndquadrant(dot)com> writes:
> > On 2014-11-01 14:39:21 -0400, Tom Lane wrote:
> >> What exactly do you think is going to make a crashed unlogged index valid
> >> again without a REINDEX? Certainly the people who are currently using
> >> hash indexes in the way Andrew describes are expecting to have to REINDEX
> >> them after a crash.
>
> > Obviously that individual index needs to be recreated. What I mean is
> > that I don't think it'll be acceptable that the table essentially can't
> > be queried before that's done. The situations in which I'd found
> > unlogged indexes useful is where there's some indexes are critical for
> > the OLTP business (those would continue to be logged), but some other
> > large ones are for things that aren't absolutely essential. Reports and
> > such.
>
> Sure. And as long as you aren't issuing queries that would want to scan
> the crashed index, it won't matter either way. The question is whether
> you'd rather that your "inessential reporting queries" fail without the
> broken index, or that they take extreme amounts of time/resources.
> I don't think it's obvious that the first alternative is bad.

In some of these cases the unlogged index would still be used for a
subset of the OLTP workload, e.g. because they're smaller. We e.g. have
a client that has smaller (as in 50GB instead of 600GB) indexes for rows
of a certain type in the table, but also one that spans the whole thing.

Greetings,

Andres Freund

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