Re: Optimizer showing wrong rows in plan - Mailing list pgsql-performance

From Tadipathri Raghu
Subject Re: Optimizer showing wrong rows in plan
Date
Msg-id 645d9d71003280033l16069edcp45d9bbb0e7ed5517@mail.gmail.com
Whole thread Raw
In response to Re: Optimizer showing wrong rows in plan  (Szymon Guz <mabewlun@gmail.com>)
Responses Re: Optimizer showing wrong rows in plan
List pgsql-performance
Hi Guz,
 
It is assuming that there are 2400 rows in this table. Probably you've deleted some rows from the table leaving just one.
 
Frankly speaking its a newly created table without any operation on it as you have seen the example. Then how come it showing those many rows where we have only one in it.
Thanks if we have proper explination on this..
 
Regards
Raghavendra

 
On Sun, Mar 28, 2010 at 12:59 PM, Szymon Guz <mabewlun@gmail.com> wrote:


2010/3/28 Tadipathri Raghu <traghu.dba@gmail.com>
Hi Guz,
 
Thank you for the prompt reply.
 
No, the optimizer is not retrieving anything, it just assumes that there are 2400 rows because that is the number of rows that exists in the statictics for this table. The optimizer just tries to find the best plan and to optimize the query plan for execution taking into consideration all information that can be found for this table (it also looks in the statistics information about rows from this table).
 
So, whats it assuming here as rows(2400).  Could you explain this.
 


It is assuming that there are 2400 rows in this table. Probably you've deleted some rows from the table leaving just one.

regards
Szymon Guz 


pgsql-performance by date:

Previous
From: Szymon Guz
Date:
Subject: Re: Optimizer showing wrong rows in plan
Next
From: Tadipathri Raghu
Date:
Subject: Re: Optimizer showing wrong rows in plan