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Old 01-13-2012, 10:08 AM   #1
rajaniyer123
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High I/O wait observed in Linux based Oracle Database Server


Hi,

We have just migrated Oracle Database from Solaris Server to Linux VM [ESX] server.

We have observed that there is high I/O wait issues while database query is running on Linux VM, which was ideally zero in case of Solaris.

In the same ref. please let me know, is there any tunning need to be done from linux side.

Please suggest.
 
Old 01-13-2012, 10:26 AM   #2
TB0ne
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Quote:
Originally Posted by rajaniyer123 View Post
Hi,
We have just migrated Oracle Database from Solaris Server to Linux VM [ESX] server.

We have observed that there is high I/O wait issues while database query is running on Linux VM, which was ideally zero in case of Solaris. In the same ref. please let me know, is there any tunning need to be done from linux side.
Please suggest.
No idea, since there aren't enough details. Solaris probably wasn't running on a VM, and you don't tell us anything about how big that box was (CPU/Memory/disk/etc.), and you don't tell us what version/distro of Linux, or how you have the VMware box set up, and what resources you have assigned to that instance, or how big the database is, and on what kind of disk it's running and how many spindles.

Check the outputs of iostat/sar/top, and see what usages you're getting. Check the Oracle installation docs, and make sure you followed them for Linux installation.

Best thing to do would be to call Oracle support, since you're paying for it. They can run traces, and tell you where the bottleneck is.
 
Old 01-14-2012, 07:51 AM   #3
markseger
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if you're referring to the CPU time spent in i/o wait, this is probably the most useless number I've ever seen, though I'm happy to be corrected.

My understanding is all this means is the cpu is NOT doing anything while there is I/O going on. In fact in at least collectl, I don't even include it in the total cpu time.

I have done numerous experiments to prove my case. For example, if you fire up a dt (or other disk load generator tool) you'll always see a high i/o wait. If in parallel you start a compute bound process you'll see the iowait drop, since now the cpu has something else to do with its free time.

While I know nothing about solaris, one should be careful not to confuse a counter name from one O/S with another.

-mark
 
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Old 01-16-2012, 09:00 PM   #4
jlliagre
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As already pointed by markseger, the i/o wait counter is more confusing than anything useful, especially with modern (multi-core, multi-thread) architectures. That's the reason why Solaris ceased to report anything but zero in it since Solaris 10 (2005).
 
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