Re: postgres 7.4 vs 8.x redux: query plans

On 4/3/07, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> "Alex Deucher" <alexdeucher(at)gmail(dot)com> writes:
> > Turning off bitmapscan ends up doing a sequential scan. Turning off
> > both bitmapscan and seqscan results in a bitmap heap scan. It doesn't
> > seem to want to use the index at all. Any ideas?
>
> The "ORed indexscans" plan style that was in 7.4 isn't there anymore;
> we use bitmap OR'ing instead. There actually are repeated indexscans
> hidden under the "= ANY" indexscan condition in 8.2, it's just that
> the mechanism for detecting duplicate matches is different. AFAIK the
> index access costs ought to be about the same either way, and the other
> costs the same or better as what we did in 7.4. It's clear though that
> 8.2 is taking some kind of big hit in the index access in your case.
> There's something very strange going on here.
>
> You do have both lc_collate and lc_ctype set to C, right? What about
> database encoding?
>

hmmm... ok, this is weird. performance seems to have improved
significantly after I reloaded postgres after adding some hew hosts to
the pg_hba.conf. I'll run some more tests and let you know what
happens.

Alex