Re: hash index on unlogged tables doesn't behave as expected

On Thu, Sep 21, 2017 at 8:16 PM, Kyotaro HORIGUCHI
<horiguchi.kyotaro@lab.ntt.co.jp> wrote:
> Though I don't see it's bug and agree that the message is not
> proper, currently we can create hash indexes without no warning
> on unlogged tables and it causes a problem with replication.

That's true, but I don't believe it's a sufficient reason to make a change.

Before 84aa8ba128a08e6fdebb2497c7a79ebf18093e12 (2014), we didn't
issue a warning about hash indexes in any case whatsoever; we relied
on people reading the documentation to find out about the limitations
of hash indexes.  They can still do that in any cases that the warning
doesn't adequately cover.  I really don't think it's worth kibitzing
the cases where this message is emitted in released branches, or the
text of the message, just as we didn't back-patch the message itself
into older releases that are still supported.  We need a compelling
reason to change things in stable branches, and the fact that a
warning message added in 2014 doesn't cover every limitation of a
pre-1996 hash index implementation is not an emergency.  Let's save
back-patching for actual bugs, or we'll forever be fiddling with
things in stable branches that would be better left alone.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company