title: Slow sql select with index on postgres
body: <p>I have a production database which is replicated to a another host using londist. The table looks like</p>
  
  <pre><code># \d+ usermessage
                 Table "public.usermessage"
    Column       |       Type        | Modifiers | Description
  -------------------+-------------------+-----------+-------------
   id                | bigint            | not null  |
   subject           | character varying |           |
   message           | character varying |           |
   read              | boolean           |           |
   timestamp         | bigint            |           |
   owner             | bigint            |           |
   sender            | bigint            |           |
   recipient         | bigint            |           |
   dao_created       | bigint            |           |
   dao_updated       | bigint            |           |
   type              | integer           |           |
   replymessageid    | character varying |           |
   originalmessageid | character varying |           |
   replied           | boolean           |           |
   mheader           | boolean           |           |
   mbody             | boolean           |           |
  Indexes:
  "usermessage_pkey" PRIMARY KEY, btree (id)
  "usermessage_owner_key" btree (owner)
  "usermessage_recipient_key" btree (recipient)
  "usermessage_timestamp_key" btree ("timestamp")
  "usermessage_type_key" btree (type)
  Has OIDs: no
  </code></pre>
  
  <p>If executed on the replicated database, the select is fast as expected, if executed on the production host it's horrible slow. To make things more strange, not all timestamps are slow, some of them are fast on both hosts. The filesystem and the storage behind the production host is fine and not under heavy usage. Any ideas?</p>
  
  <pre><code>replication# explain analyse SELECT COUNT(id) FROM usermessage WHERE owner = 1234567 AND timestamp &gt; 1362077127010;
                                                                   QUERY PLAN
  ----------------------------------------------------------------------------------------------------------------------------------------------------
   Aggregate  (cost=263.37..263.38 rows=1 width=8) (actual time=0.059..0.060 rows=1 loops=1)
     -&gt;  Bitmap Heap Scan on usermessage  (cost=259.35..263.36 rows=1 width=8) (actual time=0.055..0.055 rows=0 loops=1)
           Recheck Cond: ((owner = 1234567) AND ("timestamp" &gt; 1362077127010::bigint))
           -&gt;  BitmapAnd  (cost=259.35..259.35 rows=1 width=0) (actual time=0.054..0.054 rows=0 loops=1)
                 -&gt;  Bitmap Index Scan on usermessage_owner_key  (cost=0.00..19.27 rows=241 width=0) (actual time=0.032..0.032 rows=33 loops=1)
                       Index Cond: (owner = 1234567)
                 -&gt;  Bitmap Index Scan on usermessage_timestamp_key  (cost=0.00..239.82 rows=12048 width=0) (actual time=0.013..0.013 rows=0 loops=1)
                       Index Cond: ("timestamp" &gt; 1362077127010::bigint)
   Total runtime: 0.103 ms
  (9 rows)
  
  production#  explain analyse SELECT COUNT(id) FROM usermessage WHERE owner = 1234567 AND timestamp &gt; 1362077127010;
                                                                          QUERY PLAN
  ------------------------------------------------------------------------------------------------------------------------------------------------------------------
   Aggregate  (cost=267.39..267.40 rows=1 width=8) (actual time=47536.590..47536.590 rows=1 loops=1)
     -&gt;  Bitmap Heap Scan on usermessage  (cost=263.37..267.38 rows=1 width=8) (actual time=47532.520..47536.579 rows=3 loops=1)
           Recheck Cond: ((owner = 1234567) AND ("timestamp" &gt; 1362077127010::bigint))
           -&gt;  BitmapAnd  (cost=263.37..263.37 rows=1 width=0) (actual time=47532.334..47532.334 rows=0 loops=1)
                 -&gt;  Bitmap Index Scan on usermessage_owner_key  (cost=0.00..21.90 rows=168 width=0) (actual time=0.123..0.123 rows=46 loops=1)
                       Index Cond: (owner = 1234567)
                 -&gt;  Bitmap Index Scan on usermessage_timestamp_key  (cost=0.00..241.22 rows=12209 width=0) (actual time=47530.255..47530.255 rows=5255617 loops=1)
                       Index Cond: ("timestamp" &gt; 1362077127010::bigint)
   Total runtime: 47536.668 ms
  (9 rows)
  </code></pre>