RE: Database performance during hot backup
- From: "Hameed, Amir" <Amir.Hameed@xxxxxxxxx>
- To: <jonathan@xxxxxxxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 30 Mar 2012 13:03:05 -0400
Thanks Jonathan.
A little bit more information on the way we are conducting these tests.
We are in the process of implementing hot backup in our Oracle FMW SOA
suite environment and we are trying to assess if our users could
potentially experience any slowdown during the backup process so that we
can set their expectations accordingly. The FMW BPEL console provides a
facility where you could simulate the load that you would run in
real-life (think time, iterations, etc.) on various services. The
majority of the BPEL statements are INSERT based because they insert
data into the database. We are running tests with two scenarios: (a) DB
not in hot backup mode (b) DB in hot backup mode. During our test, we
are NOT actually snapping the backup (we are using EMC NAS for this RAC
database and use the snap technology for backup) at the storage level.
The BPEL console is reporting that when the DB was not in hot backup
mode, the transaction timings were much better than when it was in hot
backup mode. I have not actually run AWR during the test to see whether
it is the LGWR that is causing the issue or something else. I just
wanted to find out first, at a high level, whether to expect any
performance degradation during hot backups or not.
Thanks
Amir
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Jonathan Lewis
Sent: Friday, March 30, 2012 12:22 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Database performance during hot backup
If you're doing a backup you're presumably copying the database files -
which may mean that every db file read is a little slower, which may be
enough to slow down the DML - especially since DML often requires
indexes
to be maintained and index maintenance often leads to random single
block
reads. The I/O due to backing up could also slow down the log file
parallel
writes, increasing the time for log file sync waits.
Given that you could be increasing the size and number of writes to the
log
file you've got another reason for seeing slower DML times, even if the
log
writes isn't under any particularly heavy load.
Regards
Jonathan Lewis
http://jonathanlewis.wordpress.com
Oracle Core (Apress 2011)
http://www.apress.com/9781430239543
----- Original Message -----
From: "Hameed, Amir" <Amir.Hameed@xxxxxxxxx>
To: <oracle-l@xxxxxxxxxxxxx>
Sent: Friday, March 30, 2012 2:37 PM
Subject: Database performance during hot backup
Folks,
I am trying to understand if it is expected to see performance
degradation of DML transactions that are active during a hot backup. It
is my understanding that the only noticeable thing that happens during a
hot backup for DML statement is an increase in the amount of redo
generation and that is because Oracle starts to log full images of data
blocks before a change is made to a data block. I am not aware of any
impact on performance while in hot backup mode, unless the LGWR is being
constrained for some reason.
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