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Re: Odd out of memory problem.

From: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
To: Andrew Dunstan <andrew(at)dunslane(dot)net>
Cc: PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Odd out of memory problem.
Date: 2012-03-26 16:11:25
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Lists: pgsql-hackers
Andrew Dunstan <andrew(at)dunslane(dot)net> writes:
> On 03/26/2012 11:18 AM, Tom Lane wrote:
>> Could we see EXPLAIN output for this query?

> Currently it shows:

> Limit  (cost=19443025.87..19443025.89 rows=10 width=8
>    ->  Sort  (cost=19443025.87..19446451.29 rows=1370168 width=8)
>          Sort Key: (max(pageno))
>          ->  GroupAggregate  (cost=18537785.99..19413417.03 rows=1370168 
> width=8)
>                ->  Sort  (cost=18537785.99..18823953.97 rows=114467192 
> width=8)
>                      Sort Key: loid
>                      ->  Seq Scan on ldata  (cost=0.00..1651163.92 
> rows=114467192 width=8)

> The table might have been analysed since I ran the query, though.

That plan should not create a tuple hash table, so I think it's almost
certain that the plan changed.  It might be interesting to remove the
pg_statistic rows for the table and then see what plan you get.

> To answer Hans' question, we have seen the problem in other contexts. We 
> first noticed this problem in a failure to restore large objects when 
> running pg_restore.

[ scratches head... ]  I don't understand how or why pg_restore would be
executing such a query.

			regards, tom lane

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