From: | Giorgio Valoti <giorgio_v(at)mac(dot)com> |
---|---|
To: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Query Plan choice with timestamps |
Date: | 2008-08-07 12:30:51 |
Message-ID: | 15821866-9564-40E8-BC12-52ADD6D6EEA5@mac.com |
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Thread: | |
Lists: | pgsql-performance |
On 07/ago/08, at 10:35, Richard Huxton wrote:
> Giorgio Valoti wrote:
>> Hi, I have a timestamptz field that I want to use with a query, but
>> I don’t need the full timestamp resolution, so I’ve created a
>> day_trunc(timestamptz) immutable function which I’ll use with the
>> query and with a new index:
>> logs=> create index test_idx on blackbox (day_trunc(ts));
>> However, the query plan doesn’t use the index:
>
> Does it use it ever? e.g. with
> SELECT * FROM blackbox WHERE day_trunk(ts) = '...'
It’s used:
logs=> explain select * from blackbox where day_trunc(ts) =
day_trunc(now());
QUERY PLAN
---------------------------------------------------------------------------
Bitmap Heap Scan on blackbox (cost=22.38..3998.43 rows=1239
width=264)
Recheck Cond: (day_trunc(ts) = day_trunc(now()))
-> Bitmap Index Scan on date_idx (cost=0.00..22.07 rows=1239
width=0)
Index Cond: (day_trunc(ts) = day_trunc(now()))
--
Giorgio Valoti
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