Re: Update takes longer than expected

Andy Chambers <achambers(at)mcna(dot)net> writes:
> I have an update that takes longer than expected and wondered if
> there's an easy way to make it go faster.

> It's pretty simple:-

> create table session (
> id serial primary key,
> data text);

> update session
> set data = 'ipsum lorem...'
> where id = 5;

> The "ipsum lorem.." stuff is an encrypted session variable from a
> rails app that does tend to get quite large

> select avg(length(data)) from session
> => 31275

> We're trying to migrate the app from mysql to pg and this is one of
> the performance bottle-necks. Unfortunately it slows down every
> request by about 5 seconds.

5 seconds!? I tried this example (with 31K of random data in the
literal) and got timings in the 10-to-15-millisecond range. And that's
with a debug build on an old, slow machine. There's something
drastically wrong with your setup, but there's not enough information
here to guess what.

regards, tom lane