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Using ionice for Oracle?

Oracle Database Tips by Donald BurlesonApril 16, 2015

 

The UNIX/Linux nice command is a powerful tool for adjusting the dispatching priorities of Oracle background processes and batch jobs, an important part of the advanced DBA toolset.

Now Linux brings a related utility called ionice, a command which alters the dispatching for I/O devices.

This article describes the Linux ionice utility and how it might be used in an Oracle environment:

"The best usecase for using ionice to improve performance is when you need to do two classes of tasks at once: The ones that don't use much disk IO but demand fast response, and the ones that do a LOT of disk IO but don't need it done urgently.

For example, think of some of the time-consuming things you want to do in the background, like:

  • Downloading a torrent on a fast internet link that creates a great deal of disk seeking.
  • Copy a huge file between two locations
  • Perform a system backup
  • Install your latest set up system updates

Most of the time, you really don't care how fast (within reason) these tasks take, as long as your desktop applications don't lag like hell! This is where ionice comes to the rescue. You can, in effect, tell Linux to only give disk access to these programs when nothing else wants it.

The command for doing this is sudo ionice -c3 -ppid, where pid is the numeric Process ID of the task you want to reschedule."

So, are there legitimate uses for ionice in an Oracle database environment?  Oracle ACE Steve Karam notes:

"The ionice command looks neat but I wouldn't use it for Oracle. Perhaps with very careful analysis it could be attempted, but for the most part Oracle handles the priorities properly and the CFQ elevator handles I/O scheduling properly.

Technically we can since by default, RH4.0 systems are using the CFQ I/O elevator by default, but if you consider the way Oracle writes with a combination of server processes (direct writes) and background processes (DBWR, LGWR, ARC0-9, DBWR slaves, etc) you could seriously harm the balance of your system."

John Garmany also notes "ionice looks like a cool utility but I can not find it for RedHat v4 so I can not test it on my server.  It looks from the note that it is a late addition.  The kernel listed in the blog is for RHv5 (which I do not currently have a system running). I would think it would be something you could add to a backup script or export.  Adding it to the shell script would ionice everything run in that script.  But the database connection would be a different process and probably would not be impacted."

 

If you like Oracle tuning, you might enjoy my book "Oracle Tuning: The Definitive Reference", with 950 pages of tuning tips and scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


 

 

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