RE: query and delete records really slow in a table

From: Elliott, Patrick <patrick.elliott_at_medtronic.com>
Date: Fri, 19 Oct 2007 09:17:35 -0500
Message-ID: <3B8B6A1700202C43A89D61CE495C894E0C03A55BD4@MSPM1BMSGM103.ent.core.medtronic.com>

If that explain plan is for deleting one row, then it is not a good explain plan. It is doing a full table scan in the child table for every row in the parent. Did you analyze the tables with histograms? (i.e. for all indexed columns)

Pat

-----Original Message-----

From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Koppelaars, Toon Sent: Friday, October 19, 2007 8:06 AM
To: legedoos_at_gmail.com; oracle-l_at_freelists.org Subject: RE: query and delete records really slow in a table

Rob,

Can you share the delete statement text?
Is the index structure on all involved foreign keys the same (on this and the other database)?
Can perform a sql-trace of both cases (fast and slow)?

Toon

-----Original Message-----

From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of LegeDoos Sent: vrijdag 19 oktober 2007 14:29
To: oracle-l_at_freelists.org
Subject: query and delete records really slow in a table

Hi there!

We have a couple (18) of tables "linked" with foreign keys and cascading delete. The largest table contains < 1.000.000 records.

When deleting a record from the top level table, this is extremely slow (like waiting a couple of minutes). On another database (on the same server and on another server) deleting is fast (<1sec). Tables contain defferent data.

-There are no blocking locks
-rebuilding the indexes didn't help
-the explain plan looks ok and is the same for the different databases

0 DELETE STATEMENT optimizer=ALL_ROWS (cost=460 card=1 bytes=73)

1       0         DELETE of 'OST_STUDENT_STUDIEVOORTGANG'
2       1           HASH JOIN (SEMI) (cost=460 card=1 bytes=73)
3       2             TABLE ACCESS (FULL) of

'OST_STUDENT_STUDIEVOORTGANG' TABLE
(cost=57 card=31859 bytes=1146924)
4 2 TABLE ACCESS (FULL) of 'OST_STUDENT_EXAMEN' TABLE (cost=199
card=55431 bytes=2050947)

-I moved all tables en indexes to another tablespace, didn't help -There are no errors in the alert.log.

Can anybody help?

Thanks!

Rob
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http://www.freelists.org/webpage/oracle-l Received on Fri Oct 19 2007 - 09:17:35 CDT