Re: Database performance during hot backup
- From: "Jonathan Lewis" <jonathan@xxxxxxxxxxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 30 Mar 2012 17:21:46 +0100
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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