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

 

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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