Re: Ignore hash indices on replicas

On Aug 19, 2012, at 2:37 PM, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:

> On Tue, 2012-07-10 at 00:09 -0700, Steven Schlansker wrote:
>> I understand that the current wisdom is "don't use hash indices", but
>> (unfortunately?) I have benchmarks that
>> show that our particular application is faster by quite a bit when a
>> hash index is available.
>
> Can you publish the results somewhere? It might provoke some interest.

I might be able to spend some time looking at making this public, but the general parameters are:

122M rows, lookup key is a UUID type. Lookups are ~1000 random keys at a time (as in, a giant SELECT * FROM table WHERE key IN (?,?,?,?,…)

>
>> I assume that fixing the hash index logging issue hasn't been a
>> priority due to low interest / technical limitations, but I'm curious
>> for a stopgap measure -- can we somehow configure Postgres to ignore
>> hash indices on a replica, using other b-tree indices or even a
>> sequential scan? I know I can do this on a per-connection basis by
>> disabling various index lookup methods, but it'd be nice if it just
>> ignored invalid indices on its own.
>
> This might work for you:
>
> http://sigaev.ru/git/gitweb.cgi?p=plantuner.git;a=blob;hb=HEAD;f=README.plantuner

Thanks for the link; that looks interesting. It is a bit unfortunate that I would have to find and exclude indices manually, but very doable...