From: Christopher Browne <cbbrowne@libertyrms.info>
Subject: Re: indexing timestamp fields
Date: Wed, 15 Oct 2003 17:31:21 -0400
Organization: Hub.Org Networking Services
Lines: 37
Message-ID: <607k36w5li.fsf@dev6.int.libertyrms.info>
References: <bmjqo8$1hve$1@news.hub.org>
	<60wub6wjxf.fsf@dev6.int.libertyrms.info>
	<bmkafb$aiu$1@news.hub.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
User-Agent: Gnus/5.1003 (Gnus v5.10.3) XEmacs/21.4 (Reasonable Discussion,
	linux)
Cancel-Lock: sha1:FMYEIigJBx7t8h6UYIU8FIDDMxA=
To: pgsql-sql@postgresql.org

teknokrat <teknokrat@yahoo.com> writes:
> Christopher Browne wrote:
>
>> teknokrat <teknokrat@yahoo.com> writes:
>>
>>>Is it a good idea to index timestamp fields? what about date fields in
>>>general?
>> If you need to order by a timestamp, then it can be worthwhile.
>> If that timestamp can be null, and is rarely populated, then you
>> might
>> get a _big_ benefit from creating a partial index as with:
>>  create index by_some_date on my_table(some_date) where some_date is
>>    not null;
>
> I have a lot of queries of the " where timestamp < some date " type
> and was wondering if an index would improve performance. None of the
> timestamps are null and they are always populated

There isn't a single straight answer on this.  
It _might_ help; it might not.  

- It might be that adding "timestamp" to some existing index would be
better still.

- If the table is real big, and the "ts < other_ts" doesn't restrict
things very much, then you may merely sit in between an index scan
that touches every page of the table and a Seq Scan that does the
same.

Try creating the index, and do some EXPLAIN ANALYZE queries to see
what happens; that should give you an idea as to how effective this
is.
-- 
output = ("cbbrowne" "@" "libertyrms.info")
<http://dev6.int.libertyrms.com/>
Christopher Browne
(416) 646 3304 x124 (land)