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From "Tiwari, Dushyant" <Dushyant.Tiw...@morganstanley.com>
Subject RE: Mutation Dropped Messages
Date Mon, 05 Mar 2012 11:40:18 GMT
Thanks a lot for the concurrent_writes hint that really improves the throughput. Do you mean
dropped messages and no timedoutexception will mean the data is written somewhere in the cluster
and by taking corrective measures desired CL can be achieved?



From: aaron morton [mailto:aaron@thelastpickle.com]
Sent: Monday, March 05, 2012 4:15 PM
To: user@cassandra.apache.org
Subject: Re: Mutation Dropped Messages

1.       Which parameters to tune in the config files? - Especially looking for heavy writes
The node is overloaded. It may be because there are no enough nodes, or the node is under
temporary stress such as GC or repair.
If you have spare IO / CPU capacity you could increase the current_writes to increase throughput
on the write stage. You then need to ensure the commit log and, to a lesser degree, the data
volumes can keep up.

2.       What is the difference between TimedOutException and silently dropping mutation messages
while operating on a CL of QUORUM.
TimedOutExceptions means CL nodes did not respond to the coordinator before rpc_timeout. Dropping
messages happens when a message is removed from the queue in the a thread pool after rpc_timeout
has occurred. it is a feature of the architecture, and correct behaviour under stress.
Inconsistencies created by dropped messages are repaired via reads as high CL, HH (in 1.+),
Read Repair or Anti Entropy.

Cheers

-----------------
Aaron Morton
Freelance Developer
@aaronmorton
http://www.thelastpickle.com

On 5/03/2012, at 11:32 PM, Tiwari, Dushyant wrote:


Hi All,

While benchmarking Cassandra I found "Mutation Dropped" messages in the logs.  Now I know
this is a good old question. It will be really great if someone can provide a check list to
recover when such a thing happens. I am looking for answers of the following questions  -

1.       Which parameters to tune in the config files? - Especially looking for heavy writes
2.       What is the difference between TimedOutException and silently dropping mutation messages
while operating on a CL of QUORUM.


Regards,
Dushyant
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NOTICE: Morgan Stanley is not acting as a municipal advisor and the opinions or views contained
herein are not intended to be, and do not constitute, advice within the meaning of Section
975 of the Dodd-Frank Wall Street Reform and Consumer Protection Act. If you have received
this communication in error, please destroy all electronic and paper copies and notify the
sender immediately. Mistransmission is not intended to waive confidentiality or privilege.
Morgan Stanley reserves the right, to the extent permitted under applicable law, to monitor
electronic communications. This message is subject to terms available at the following link:
http://www.morganstanley.com/disclaimers. If you cannot access these links, please notify
us by reply message and we will send the contents to you. By messaging with Morgan Stanley
you consent to the foregoing.

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