RE: Jumbo frames and NIC settings

  • From: "Herring, David" <HerringD@xxxxxxx>
  • To: "oracle-l@xxxxxxxxxxxxx" <oracle-l@xxxxxxxxxxxxx>
  • Date: Wed, 18 Jun 2014 12:41:23 -0500

FYI, Oracle came back with roughly what I expected - they only care about MTU 
and any NIC-specific settings should be determined by the vendor.  The good 
news is now I can force parallelism to be addressed if they want to benefit 
from jumbo frames.

Dave Herring

-----Original Message-----
From: Herring, David 
Sent: Monday, June 16, 2014 4:30 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: Jumbo frames and NIC settings

Folks,

I'm looking for a bit of help related to NIC settings on 11.2.0.3.9, 4-node 
cluster on RH, with jumbo frames.

We've run into a situation where an existing RAC had jumbo frames recently 
added.  Shortly afterwards some of the instances crashed when interconnect 
traffic became particularly heavy.  The sysadmins noted that the cards were 
flapping and sought changes on the cards themselves.  They pulled in RedHat and 
RH had them increase the ring buffer size from 255 (default) to 4096 and then 
set tcp segmentation offload to "off".  These changes helped a bit but 
eventually we had to turn off jumbo frames because 1 or more instances kept 
crashing.

The real issue is with the interconnect traffic and it's due to ridiculous 
parallelism settings combined with high concurrent parallel queries.  
Unfortunately my hands are tied at the moment on addressing this.  What I'd 
like to do is make sure all settings across the board are intelligently set and 
since RH came in and suggested these changes, I started wondering if there were 
any best practices that others have set related to RAC and jumbo frames.

I opened an SR with Oracle asking for their recommendations (which I expect 
will be "mtu at 9000") but I don't have too high of expectations on this.

Dave
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