Skip site navigation (1) Skip section navigation (2)

Re: Query performance

From: S Arvind <arvindwill(at)gmail(dot)com>
To: pgsql-performance(at)postgresql(dot)org
Subject: Re: Query performance
Date: 2009-10-12 12:39:39
Message-ID: abf9211d0910120539n7c45a6bdkd49588d2154d5a41@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-performance
I can understand left join, actually can any one tell me why sort operation
is carried out and wat Materialize means...
Can anyone explain me the mentioned plan with reason(s)?


-Arvind S


2009/10/12 Grzegorz Jaśkiewicz <gryzman(at)gmail(dot)com>

>
>
> On Mon, Oct 12, 2009 at 12:21 PM, S Arvind <arvindwill(at)gmail(dot)com> wrote:
>
>> In the below query both table has less than 1 million data. Can u tell me
>> the reason of this plan?
>> why its takin extensive cost , seq scan and sorting?? wat is Materialize?
>>
>> select 1 from  service_detail
>> left join non_service_detail on non_service_detail_service_id =
>> service_detail.service_detail_id
>>
>>
>>
>> Merge Left Join  (cost=62451.86..67379.08 rows=286789 width=0)
>>   Merge Cond: (service_detail.service_detail_id =
>> non_service_detail.non_service_detail_service_id)
>>   ->  Sort  (cost=18610.57..18923.27 rows=125077 width=8)
>>         Sort Key: service_detail.service_detail_id
>>         ->  Seq Scan on service_detail  (cost=0.00..6309.77 rows=125077
>> width=8)
>>   ->  Materialize  (cost=43841.28..47426.15 rows=286789 width=8)
>>         ->  Sort  (cost=43841.28..44558.26 rows=286789 width=8)
>>               Sort Key: non_service_detail.non_service_detail_service_id
>>               ->  Seq Scan on non_service_detail  (cost=0.00..13920.89
>> rows=286789 width=8)
>>
>> A) it is a left join, meaning - everything is pulled from left side,
> B) there are no conditions, so ... ... everything is pulled again from left
> side.
>
>
>
>
> --
> GJ
>

In response to

Responses

pgsql-performance by date

Next:From: Matthew WakelingDate: 2009-10-12 13:01:55
Subject: Re: Query performance
Previous:From: Grzegorz JaśkiewiczDate: 2009-10-12 12:30:12
Subject: Re: Query performance

Privacy Policy | About PostgreSQL
Copyright © 1996-2014 The PostgreSQL Global Development Group