From: Russell Smith <mr-russ@pws.com.au>
To: Pavel Stehule <pavel.stehule@gmail.com>
Cc: David West <david.west@cusppoint.com>
Cc: pgsql-performance@postgresql.org
Subject: Re: limit clause breaks query planner?
Date: Tue, 02 Sep 2008 13:54:53 +1000
Message-ID: <48BCB90D.8090606@pws.com.au> (raw)
In-Reply-To: <162867790809011217n587e6090qdec2c4c6a1f580e6@mail.gmail.com>
References: <1683189597512580954@unknownmsgid>
<162867790809010552o624a347aif0eb5fc71e7bbad@mail.gmail.com>
<2934211014530751484@unknownmsgid>
<162867790809011217n587e6090qdec2c4c6a1f580e6@mail.gmail.com>
Pavel Stehule wrote:
> Hello
>
> 2008/9/1 David West <david.west@cusppoint.com>:
>
>> Thanks for your suggestion but the result is the same.
>>
>> Here is the explain analyse output from different queries.
>> Select * from my_table where A is null and B = '21' limit 15
>>
>> "Limit (cost=0.00..3.68 rows=15 width=128) (actual time=85837.043..85896.140 rows=15 loops=1)"
>> " -> Seq Scan on my_table this_ (cost=0.00..258789.88 rows=1055580 width=128) (actual time=85837.038..85896.091 rows=15 loops=1)"
>> " Filter: ((A IS NULL) AND ((B)::text = '21'::text))"
>> "Total runtime: 85896.214 ms"
>>
>>
[snip]
Further to Pavel's comments;
(actual time=85837.038..85896.091 rows=15 loops=1)
That's 85 seconds on a sequence scan to return the first tuple. The table is not bloated by any chance is it?
Regards
Russell
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To: pgsql-performance@postgresql.org
Cc: mr-russ@pws.com.au, pavel.stehule@gmail.com, david.west@cusppoint.com
Subject: Re: limit clause breaks query planner?
In-Reply-To: <48BCB90D.8090606@pws.com.au>
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