| From: | Merlin Moncure <mmoncure(at)gmail(dot)com> |
|---|---|
| To: | Alessandro Gagliardi <alessandro(at)path(dot)com> |
| Cc: | Scott Marlowe <scott(dot)marlowe(at)gmail(dot)com>, pgsql-performance(at)postgresql(dot)org |
| Subject: | Re: From Simple to Complex |
| Date: | 2012-02-02 14:52:17 |
| Message-ID: | CAHyXU0y5RaM6amFXnR-m=hQ0QmPsAA+Tw_erFe80JPY3_7iphQ@mail.gmail.com |
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| Lists: | pgsql-performance |
On Wed, Feb 1, 2012 at 12:48 PM, Alessandro Gagliardi
<alessandro(at)path(dot)com> wrote:
> LIMIT 65536; Total query runtime: 14846 ms.
> - http://explain.depesz.com/s/I3E
> LIMIT 69632: Total query runtime: 80141 ms.
> - http://explain.depesz.com/s/9hp
>
> So it looks like when the limit crosses a certain threshold (somewhere north
> of 2^16), Postgres decides to do a Seq Scan instead of an Index Scan.
> I've already lowered random_page_cost to 2. Maybe I should lower it to 1.5?
> Actually 60K should be plenty for my purposes anyway.
also, is effective_cache_size set to a reasonable value?
merlin
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