I increased the size of the cluster also the concurrent_writes parameter. Still there is a node which keeps on dropping the mutation messages.
Ensure all the nodes have the same spec, and the nodes have the same config. In a virtual environment consider moving the node.

Is this due to some improper load balancing? 
What does nodetool ring say and what sort of queries (and RF and CL) are you sending.

Cheers

-----------------
Aaron Morton
Freelance Developer
@aaronmorton

On 6/03/2012, at 3:58 AM, Tiwari, Dushyant wrote:

Hey Aaron,
 
I increased the size of the cluster also the concurrent_writes parameter. Still there is a node which keeps on dropping the mutation messages. The other nodes are not dropping mutation messages. I am using Hector API and had done nothing for load balancing so far. Just provided the host:port of the nodes in the Cassandrahostconfig. Is this due to some improper load balancing? Also the physical host where the node is hosted is relatively heavier than other nodes’ host. What can I do to improve?
PS: The node is seed of the cluster.
 
Thanks,
Dushyant
 
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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