Oracle-L: Hanging query puzzle

From: Thomas Jeff <ThomasJe_at_tce.com>
Date: Wed, 05 Feb 2003 09:59:27 -0800
Message-ID: <F001.0054481E.20030205095927@fatcity.com>

We have a query from a 3rd-party tool that seems to either run very quick or crawls to a complete stop.

We can find no patterns to this behavior. The hang can be experienced even when there are no other
processes active in the database. Checking waits, we see a db file scattered read.

SID EVENT                        P1TEXT                     P1 P2TEXT
P2 P3TEXT                     P3
----- ---------------------------- ------------------ ----------
------------------ ---------- ------------------ ----------
    1 pmon timer                   duration                  300
0                             0
   12 slave wait                   msg ptr            5.0440E+17
0                             0
   13 slave wait                   msg ptr            5.0440E+17
0                             0
   14 slave wait                   msg ptr            5.0440E+17
0                             0
   15 slave wait                   msg ptr            5.0440E+17
0                             0
   28 db file scattered read       file#                      12 block#
21047 blocks                      2
    5 smon timer                   sleep time                300 failed
0                             0

Then going to v$sess_io, we see the process is comletely stuck, no activity going on at all, and it's the
only active process in the database.

SID BLOCK_GETS CONSISTENT_GETS PHYSICAL_READS BLOCK_CHANGES CONSISTENT_CHANGES
----- ---------- --------------- -------------- -------------

   28    6233582        60812023       36589516       4076353
115

The query looks like this:

SELECT PRAssignment.*, SRM_RESOURCES.RESOURCE_TYPE FROM PRAssignment, SRM_RESOURCES
WHERE prModTime > TIMESTAMP '2003-02-05 09:23:56.0' AND PRAssignment.prResourceID=SRM_RESOURCES.ID

If I check the file/block values for the wait I get the prassignment table. Prassignment has 5K rows
while srm_resources has 300 rows. Prassignment also has a LONG RAW column, consequently we
see a high chain count, with the result that it's taking up 135 extents to cover those 5K rows.

I'm at a loss to explain why we see such inconsistent results with this query. Thoughts?

Thanks.

Jeffery D Thomas
DBA
Thomson Information Services
Thomson, Inc.

Email: jeff.thomas_at_thomson.net

Indy DBA Master Documentation available at: http://gkmqp.tce.com/tis_dba
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Author: Thomas Jeff
INET: ThomasJe_at_tce.com

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