Re: Out Of Memory 8.1

Thanks for the suggestion, however; this query runs in under 2 minutes (big data set) on the server it originated from, and I’m trying to ascertain why there is such a difference in performance between what should be two like for like server, as there are many other queries of a similar nature that have bigger sort operations to perform, and I honestly don’t want to have to re-write them all.

Setting enable_hashagg = off causes the query to complete, however; it means the next batch queries never completes (left it > 8 hours) when ordinarily it’s done in 5 minutes.

Thanks…

Martin.

From: scorpdaddy(at)hotmail(dot)com [mailto:scorpdaddy(at)hotmail(dot)com]
Sent: 07 April 2011 11:20
To: French, Martin; pgsql-admin(at)postgresql(dot)org
Subject: Re: [ADMIN] Out Of Memory 8.1

Have you tried moving the FROM ... WHERE ... into a sub-select? GROUP BY uses HAVING, not WHERE.

----- Reply message -----
From: "French, Martin" <frenchm(at)cromwell(dot)co(dot)uk>
Date: Wed, Apr 6, 2011 7:44 pm
Subject: [ADMIN] Out Of Memory 8.1
To: <pgsql-admin(at)postgresql(dot)org>

Hi All,

I am having problems with a query on 8.1 running on

RHEL 5.4
16GB RAM
Linux pgsql3 2.6.18-164.el5PAE #1 SMP Tue Aug 18 15:59:11 EDT 2009 i686
i686 i386 GNU/Linux
2 x Xeon X5650 (2.67GHz 6 Cores)
Disks are on PERC 6 controller in RAID 10

Postgresql.conf:
# - Memory -

shared_buffers = 327680
work_mem = 98394
maintenance_work_mem = 983040

The query:

2011-04-06 23:23:03 BST <app.charisma><26083>LOG: statement: CREATE
TABLE medusa.cmi_group_free AS
SELECT
stkl_stockno,
(SUM(stkphys) - (SUM(stkalloc) + SUM(stkbacko))) as group_free
FROM
charisma.sk_stklfl
WHERE
stkl_stockno NOT LIKE 'ZZ%' AND
stkl_stockno ~
'^([A-z&]{2,3})([0-9][0-9][0-9])([0-9][0-9][0-9][0-9][A-z0-9]{1,3})$'
GROUP BY
stkl_stockno;

The explain (cannot explain analyze, or Postgres runs out of memory
again)
'HashAggregate (cost=2731947.55..2731947.57 rows=1 width=38)'
' -> Seq Scan on stkl_rec (cost=0.00..2731947.54 rows=1 width=38)'
' Filter: (((stkl_comp)::text = 'A'::text) AND
((stkl_stockno)::text ~
'^(TK[A-Za-z0-9][0-9]{3}(?:[0-9]{5}(?:[0-9]{3,4})?)?|NSP[0-9]{3}([0-9]{4
})?|Z[MZ][0-9]{8,9}|LSP[0-9]{7}[A-Za-z0-9]|[A-Z][A-Z&][A-Z][0-9]{7}[A-Z0
-9])$'::text) AND ((stkl_stockno)::text !~~ 'ZZ%'::text) AND
((stkl_stockno)::text ~
'^([A-z&]{2,3})([0-9][0-9][0-9])([0-9][0-9][0-9][0-9][A-z0-9]{1,3})$'::t
ext))'

The table has approximately
6.9 million rows

It's not the OOM that's doing this as vm.overcommit_memory = 2 and
vm.overcommit_ratio = 90 nor is postgres swapping to disk.

Can anyone help me here? The same query on exactly the same data on an
older machine running the same setup except that it's RHEL 5.0 runs
fine!

Thanks.

Martin

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