From: | "Fernando Hevia" <fhevia(at)ip-tel(dot)com(dot)ar> |
---|---|
To: | <pgsql-sql(at)postgresql(dot)org> |
Subject: | Re: Perfomance benefit using Min() against order by & limit 1? |
Date: | 2007-10-30 21:00:42 |
Message-ID: | 06a401c81b37$eebb4260$8f01010a@iptel.com.ar |
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Thread: | |
Lists: | pgsql-sql |
Oops. Previous message went in HMTL. Sorry for that.
Text-only version follows.
---
Hi guys. Is there any difference between these two queries regarding
performance?
Table stopvoip has several million records.
I suspect using the aggregate function would be best, but benchmarking
doesnt seem to confirm it. Both queries take around 150 - 175 ms once data
has been cached.
Any hindsights?
SELECT min(h323setuptime::date)
FROM stopvoip
WHERE callingstationid = '2941605118'
AND h323setuptime >= '2007.07.01'
AND h323disconnectcause = '10'
AND acctsessiontime > 0
AND NOT calledstationid ~ '^99[89]#'
Aggregate (cost=11151.25..11151.27 rows=1 width=8)"
-> Bitmap Heap Scan on stopvoip (cost=29.29..11149.98 rows=507 width=8)
Recheck Cond: ((callingstationid)::text = '2941605118'::text)
Filter: ((h323setuptime >= '2007-07-01 00:00:00-03'::timestamp with
time zone) AND ((h323disconnectcause)::text = '10'::text) AND
(acctsessiontime > 0) AND ((calledstationid)::text !~ '^99[89]#'::text))
-> Bitmap Index Scan on idx_stopvoip_callingid2 (cost=0.00..29.29
rows=2939 width=0)
Index Cond: ((callingstationid)::text = '2941605118'::text)
SELECT h323setuptime::date
FROM stopvoip
WHERE callingstationid = '2941605118'
AND h323setuptime >= '2007.07.01'
AND h323disconnectcause = '10'
AND acctsessiontime > 0
AND NOT calledstationid ~ '^99[89]#'
ORDER BY 1
LIMIT 1
Limit (cost=11174.03..11174.03 rows=1 width=8)
-> Sort (cost=11174.03..11175.30 rows=507 width=8)
Sort Key: (h323setuptime)::date
-> Bitmap Heap Scan on stopvoip (cost=29.29..11151.25 rows=507
width=8)
Recheck Cond: ((callingstationid)::text = '2941605118'::text)
Filter: ((h323setuptime >= '2007-07-01 00:00:00-03'::timestamp
with time zone) AND ((h323disconnectcause)::text = '10'::text) AND
(acctsessiontime > 0) AND ((calledstationid)::text !~ '^99[89]#'::text))
-> Bitmap Index Scan on idx_stopvoip_callingid2
(cost=0.00..29.29 rows=2939 width=0)
Index Cond: ((callingstationid)::text =
'2941605118'::text)
Thanks,
Fernando.
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