Andres Freund <andres@2ndquadrant.com> writes:
> On 2014-09-11 13:41:37 -0400, Bruce Momjian wrote:
>> And practically, how would we implement this for upgrades? Would we have
>> pg_dump emit UNLOGGED for any hash creation command?
> That seems like an almost trivial problem in comparison to the actual
> difficulty of implementing UNLOGGED indexed on LOGGED tables.
Yeah, we'd need to somehow mark such indexes as INVALID during crash
recovery, which sounds pretty messy. We've stayed away from the whole
idea of automatically-applied catalog updates during recovery, for
good reasons.
> Yes, I
> think forbidding unlogged hash tables + teaching pg_dump a heuristic to
> treat any < 9.x hash index as unlogged would be ok.
My own opinion, if we had the infrastructure, is that "CREATE INDEX
... USING hash" should result in (1) automatically adding the UNLOGGED
attribute and (2) issuing a NOTICE or WARNING stating that we've done so.
Throwing an error, when we do not do so today, is just being a nag.
This approach also eliminates the need to do anything special in pg_dump,
which is a good thing since we have no way to retroactively fix existing
dump files.
regards, tom lane