Re: I don't understand this explain output - Mailing list pgsql-novice

From Luiz Eduardo Cantanhede Neri
Subject Re: I don't understand this explain output
Date
Msg-id 252e1f290905260252w1cc96cap4e09be4b1b3e69f9@mail.gmail.com
Whole thread Raw
In response to I don't understand this explain output  (Ron Arts <ron.arts@neonova.nl>)
List pgsql-novice
Personaly I have no ideia what's happenning but I got a suggestion that  may be a long shot, but try to vacuum de table or database.

From what I know from pg is every update / delete just happens logic, meaning that it flag the row updated as old and add a new one to file. Since you told that this table is updated every minute I thought it might have something to do with it.

On Tue, May 26, 2009 at 5:32 AM, Ron Arts <ron.arts@neonova.nl> wrote:
Hi,

I am looking at a very simple query (select * from queue),
which takes forever to finish. I don't understand the output that
explain tells me:

m=# explain select * from queue;
                        QUERY PLAN
------------------------------------------------------------
 Seq Scan on queue  (cost=0.00..635477.00 rows=1 width=402)
(1 row)

The cost seems to be very high. It's a small table (only 23 rows)
and has not seen many modifications since the table was initially
filled. OTOH many individual records are updated every minute.


If I look at anopther table in the same database:

m=# explain select * from contact;
                        QUERY PLAN
-------------------------------------------------------------
 Seq Scan on contact  (cost=0.00..183.14 rows=614 width=411)
(1 row)

and this query finishes very quickly (614 rows).


Why would a simple query be so very costly?

Thanks,
Ron Arts

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