RE: HW-enqueue wait (ASSM)
- From: "Wolfson Larry - lwolfs" <lawrence.wolfson@xxxxxxxxxx>
- To: "Oracle-L" <oracle-l@xxxxxxxxxxxxx>
- Date: Wed, 14 Oct 2009 12:00:51 -0500
Try
alter system set "_insert_enable_hwm_brokered"=false
We had a similar problem and got a response from Jonathan Lewis.
Then OS came up with the same thing after we prodded them.
Larry
According to v$lock_type, the HV enqueue is a:
"Lock used to broker the high water mark during parallel inserts"
At a guess, this means that Oracle is sharing a single extent across
multiple PX slaves while loading instead of using one extent per slave.
There seem to be two hidden parameters that might have an impact:
Name Default value Description
_ctas_hwm_brokered_loads = TRUE Enable HWM brokered CTAS
_insert_enable_hwm_brokered = TRUE during parallel inserts high water
marks
are brokered
There is also a hint HWM_BROKERED which may turn it on, but I can't see
a hint that looks like the opposite.
It's only a problem if the time spent on the HV enqueue is a significant
fraction of the total time to load - bearing in mind that the total time
is (probably) shared fairly evenly across the PX slaves - so you may
want to divide by the number of slaves before comparing.
Regards
Jonathan Lewis
________________________________
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of DBA Deepak
Sent: Wednesday, October 14, 2009 11:26 AM
To: Oracle-L
Subject: HW-enqueue wait (ASSM)
Our DB is on 11.1.0.7 (Solaris10 - sparc)
We have ASSM configured for all the segments but still we are seeing
HW-enqueue waits which contributes 60% in the overall wait time.
The DB is an OLTP DB and data insertion rate across the segments is very
high.
How to get rid of this wait event? Please help...
--
Regards,
Deepak
Oracle DBA
***************************************************************************
The information contained in this communication is confidential, is
intended only for the use of the recipient named above, and may be legally
privileged.
If the reader of this message is not the intended recipient, you are
hereby notified that any dissemination, distribution or copying of this
communication is strictly prohibited.
If you have received this communication in error, please resend this
communication to the sender and delete the original message or any copy
of it from your computer system.
Thank You.
****************************************************************************
Other related posts:
