Re: CPU Intensive query

What Postgres version is this?

8.1.3

> set enable_nestloop = off;

What's the rationale for this?

To eliminate nested loop. It does a nested loop betwwen to very large table(millions of rows).

> HashAggregate (cost=152555.97..152567.32 rows=267 width=162)

152000 disk page fetches is a bit, but it shouldn't take 24 hours. There's
probably misestimation involved at some point here. Does it really return 267
rows, or many more?

It returns finally about 19-20 thousand rows.

"Steinar H. Gunderson" <sgunderson(at)bigfoot(dot)com> wrote:
On Fri, May 18, 2007 at 09:02:52AM -0700, Abu Mushayeed wrote:
> I have an interesting problem. I have the following query that ran ok on
> Monday and Tuesday and it has been running ok since I have been at this
> job. I have seen it to be IO intensive, but since Wednesday it has become
> CPU intensive. Database wise fresh data has been put into the tables,
> vacuumed & analyzed, no other parameter has been modified.

What Postgres version is this?

> The query is as follows and it's explain plan is also attached:

Normally EXPLAIN ANALYZE data would be much better than EXPLAIN, but if the
query indeed does not finish, it's not going to help much.

> set enable_nestloop = off;

What's the rationale for this?

> HashAggregate (cost=152555.97..152567.32 rows=267 width=162)

152000 disk page fetches is a bit, but it shouldn't take 24 hours. There's
probably misestimation involved at some point here. Does it really return 267
rows, or many more?

/* Steinar */
--
Homepage: http://www.sesse.net/

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