From: | Ron Arts <ron(dot)arts(at)neonova(dot)nl> |
---|---|
To: | pgsql-novice(at)postgresql(dot)org |
Subject: | I don't understand this explain output |
Date: | 2009-05-26 08:32:03 |
Message-ID: | 4A1BA903.8020300@neonova.nl |
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Lists: | pgsql-novice |
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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