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Subject: Re: Optimizer showing wrong rows in plan
From: Szymon Guz <mabewlun@gmail.com>
To: Tadipathri Raghu <traghu.dba@gmail.com>
Cc: pgsql-performance@postgresql.org
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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

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<br><br><div class=3D"gmail_quote">2010/3/28 Tadipathri Raghu <span dir=3D"=
ltr">&lt;<a href=3D"mailto:traghu.dba@gmail.com">traghu.dba@gmail.com</a>&g=
t;</span><br><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;b=
order-left:1px #ccc solid;padding-left:1ex;">
<div>Hi=C2=A0Guz,</div>
<div>=C2=A0</div>
<div>Thank you for the prompt reply.</div><div class=3D"im">
<div>=C2=A0</div>
<blockquote style=3D"border-left:#ccc 1px solid;margin:0px 0px 0px 0.8ex;pa=
dding-left:1ex" class=3D"gmail_quote">No, the optimizer is not retrieving a=
nything, it just assumes that there are 2400 rows because that is the numbe=
r 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 ta=
king into consideration all information that can be found for this table (i=
t also looks in the statistics information about rows from this table).</bl=
ockquote>


<div>=C2=A0</div>
</div><div>So, whats it assuming here as rows(2400).=C2=A0 Could you explai=
n this.</div>
<div>=C2=A0</div>
<div><br></div></blockquote><div><br></div><div>It is assuming that there a=
re 2400 rows in this table. Probably you&#39;ve deleted some rows from the =
table leaving just one.</div><div><br></div><div>regards<br>Szymon Guz=C2=
=A0</div>
</div><br>

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