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Re: Optimization idea

From: Cédric Villemain <cedric(dot)villemain(dot)debian(at)gmail(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Vlad Arkhipov <arhipov(at)dc(dot)baikal(dot)ru>, pgsql-performance(at)postgresql(dot)org
Subject: Re: Optimization idea
Date: 2010-04-29 08:21:13
Message-ID: g2ge94e14cd1004290121rc061f11eo6bbe402634e03227@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
2010/4/29 Robert Haas <robertmhaas(at)gmail(dot)com>:
> On Wed, Apr 28, 2010 at 5:37 AM, Vlad Arkhipov <arhipov(at)dc(dot)baikal(dot)ru> wrote:
>> Even if it will be done it does not solve the original issue. If I
>> understood you right there is now no any decent way of speeding up the query
>>
>> select *
>> from t2
>> join t1 on t1.t = t2.t
>> where t1.id = X;
>>
>> except of the propagating the t1.id value to the table t2 and createing and
>> index for this column?
>
> No, what I'm saying is that if X is any ANY() expression, you can get
> a faster plan in this case by writing:
>
> SELECT * FROM t2 JOIN t1 ON t1.t = t2.t WHERE t2.id = X;

SELECT * FROM t2 JOIN t1 ON t1.t = t2.t WHERE t2.t = X;

side note : You might want/need to improve statistics in the column
t2.t (in situation/distribution like this one)

>
> For me this is about 8x faster.
>
> ...Robert
>



-- 
Cédric Villemain

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