Re: Have: Seq Scan - Want: Index Scan - what am I doing wrong?

On Tue, Oct 16, 2012 at 08:19:43PM -0400, Chris Ruprecht wrote:
>
> On Oct 16, 2012, at 20:01 , Evgeny Shishkin <itparanoia@gmail.com> wrote:
>
> > Selecting 5 yours of data is not selective at all, so postgres decides it is cheaper to do seqscan.
> >
> > Do you have an index on patient.dnsortpersonnumber? Can you post a result from
> > select count(*) from patient where dnsortpersonnumber = '347450'; ?
> >
>
> Yes, there is an index:
>
> "Aggregate  (cost=6427.06..6427.07 rows=1 width=0)"
> "  ->  Index Scan using patient_pracsortpatientnumber on patient  (cost=0.00..6427.06 rows=1 width=0)"
> "        Index Cond: (dnsortpersonnumber = '347450'::text)"
>
>
> In fact, all the other criteria is picked using an index. I fear that the >= and <= on the timestamp is causing the
issue.If I do a "=" of just one of them, I get an index scan. But I need to scan the entire range. I get queries like
"giveme everything that was entered into the system for this patient between these two dates". A single date wouldn't
work.

Have you read our FAQ on this matter?

    http://wiki.postgresql.org/wiki/FAQ#Why_are_my_queries_slow.3F_Why_don.27t_they_use_my_indexes.3F

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://enterprisedb.com

  + It's impossible for everything to be true. +