Re: Slow query: bitmap scan troubles

On Tue, Dec 4, 2012 at 9:47 AM, <postgresql(at)foo(dot)me(dot)uk> wrote:
> eagerly awaiting 6pm when I can bring the DB down and start tweaking. The
> effective_work_mem setting is going from 6Gb->88Gb which I think will make
> quite a difference.

I also wonder if increasing (say x10) of default_statistics_target or
just doing ALTER TABLE SET STATISTICS for particular tables will help.
It will make planned to produce more precise estimations. Do not
forget ANALYZE afer changing it.

>
> I still can't quite wrap around my head why accessing an index is expected
> to use more disk access than doing a bitmap scan of the table itself, but I
> guess it does make a bit of sense if postgres assumes the table is more
> likely to be cached.
>
> It's all quite, quite fascinating :)
>
> I'll let you know how it goes.
>
> - Phil
>
>
>
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