RE: enq HW - contention waits
- From: "Ric Van Dyke" <ric.van.dyke@xxxxxxxxxx>
- To: <ravigaur1@xxxxxxxxx>, "oracle-l" <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 18 Apr 2008 17:41:06 -0500
When I've run into this in the past the culprit was a table with a LOB
and the extent size was way too small. For them many times when they
hit the HWM they were also allocating more extents. In their case the
entire system was hanging when this happened because it was a very high
use table. The table was rebuild with a 256M extent size and they
didn't have the problem.
Find table (or other type of segment) that is extending frequently and
that might be the issue. You're still going to hit the HWM every now
and then, but hopefully you won't be extending the segment at the same
time.
-----------------------
Ric Van Dyke
Hotsos Enterprises
-----------------------
Hotsos Symposium 2009 dedicated to performance and nothing but
performance
March 8 - 12, 2009 in Dallas, Texas
Be there.
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Ravi Gaur
Sent: Friday, April 18, 2008 4:34 PM
To: oracle-l
Subject: enq HW - contention waits
Greetings,
We have a production database running on RAC (4-node) (10.2.0.3 on
Solaris 10) and I'm noticing a lot of waits on "enq: HW - contention".
Doing a bit of researching tells me that it is related to HWM extensions
(concurrent inserts). We have no control on the application so I wonder
what could be done from the database end to tune this up (if anything).
Here's what I see from the AWR during the time it showed up --
Top 5 Timed Events
Event
Waits
Time(s)
Avg Wait(ms)
% Total Call Time
Wait Class
CPU time
7,148
43.5
enq: HW - contention
67,034
5,263
79
32.0
Configuration
SQL*Net break/reset to client
61,006
1,504
25
9.2
Application
db file sequential read
152,431
885
6
5.4
User I/O
gc cr block busy
34,315
490
14
3.0
Cluster
Any help is deeply appreciated!!
TIA,
- Ravi Gaur
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