Increase Query Speed

[Jamie Kahgee <jamie.kahgee@xxxxxxxxx>]

I'm trying to increase my query speed for this table, it currently takes 2-3 seconds and would like to make if faster if possible.

my table reads as

       Table "public.campaign_impressions"

  Column   |            Type             |   Modifiers   

-----------+-----------------------------+---------------

 campaign  | integer                     | not null

 page      | integer                     | not null

 timestamp | timestamp without time zone | default now()

Indexes:

    "campaign_impressions_campaign_idx" btree (campaign)

    "campaign_impressions_page_idx" btree (page)

    "campaign_impressions_timestamp_idx" btree ("timestamp")

This is the type of query I do on the table (get the page and # of times for each page this campaign was viewed between date x & y)

SELECT page, COUNT(page) AS impressions

  FROM campaign_impressions

 WHERE campaign = 1 

   AND timestamp BETWEEN '2010-05-21 00:00:00' AND '2010-07-27 00:00:00'

 GROUP BY page

 ORDER BY impressions

right now I have ~13 million rows in the table, and the query seems (to me) easy enough.  but it feels like 2-3 seconds is a long time.  Is there any way I can squeeze more speed out of this?  Is there a better way to store the data for the type of info I'm trying to extract?  I'm open to all suggestions

Thanks,
Jamie K.