RE: 2-node RAC faster than 6-node!

I've been reading along and there have been several good ideas kicked around. 
However as we all know Oracle is a wonderful and complex beast. I've found the 
best approach to this type of problem solving is to rely on Oracle's 
instrumentation of the database. ie. the Wait Events. I'm a little surprised 
that there was only brief mention of running a AWR report (from Alex I 
believe). Just about everything you need to diagnose this problem can be found 
there. You should use a consistent work load, run the report for a narrow 
period of time (perhaps 15-30 minutes) and run one for each configuration (1 
node, 2 nodes, 3 nodes, ...). You may find that running 10046 session traces 
will also be helpful. Remember you are looking for your top waits. Where is the 
database spending most of its time.
 
Take a look at your top 5 wait events and do a little online research. Other 
areas of interest would be the RAC Statistics -- Avg global cache cr block 
receive time and Avg global cache current block receive time in particular. 
Also take a quick look at your IO Stats and Top SQL Statements. Focus on the 
statements sorted by the type of wait Oracle spends most of its time on. For 
example if CPU show on the top of your top 5 wait events then look at SQL 
sorted by CPU. 
 
You will find alot of good information out on the Web regarding thresholds and 
what to look for. For example what the normal range and upper bounds on the 
interconnect statistics.
 
Hope this helps.
 
    -Randy

  _____  

From: oracle-l-bounce@xxxxxxxxxxxxx [mailto:oracle-l-bounce@xxxxxxxxxxxxx] On 
Behalf Of Alex Gorbachev
Sent: Thursday, April 03, 2008 10:49 PM
To: Oracle-L Freelists
Subject: Re: 2-node RAC faster than 6-node!


I'm going to drag this into slightly different direction (yeah right - what 
else can you expect from me?;)

This thread is full of assumptions leading to interesting guesses. Pretty much 
all of them have their chance to happen and many more exist. Though, there were 
few suggestions to proceed with rather standard performance troubleshooting. 
However, OP expressed his interest in silver bullets - "I was just trying to 
see if anyone can help pinpoint us on areas to focus on as possible culprits". 
Everything is possible and many things are arguably probable. 

This is not to discourage the answers and ideas in the cases that don't really 
have a clear investigation paths and methods to gather more information. But in 
this case there is only vague description of a complex system and not a single 
performance metric collections ("improved significantly" and "in some cases 20X 
faster" don't count). Any RAC system is quite complex (and 6 nodes cluster is 
not the least complex) and tuning by silver bullets would traditionally be 
longer/more expensive/complex/prone to errors. There are much better 
investigation paths to take.

My rant is over... please continue. :-)

Alex


On 3-Apr-08, at 7:44 PM, 조동욱 wrote:


I doubt if OP has a mal-configured network setting.
It's possible that 6-node RAC performs poorer than 2-node RAC.
But 20X time? No way.

If the application access pattern and workload are same, the only culprits are 
poor interconnect or storage. 
I recommend to monitor OS level network statistics, configuration and plus, 
Oracle cluster wait events.

Dion Cho

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