1.       One node is running at 8G rest on 10G – same config

2.       Nodetool –

Status State   Load            Owns    Token

                                                                               162563731948587347959549934419333022646

Up     Normal  107.79 MB       25.00%  34957844353235424160784456632419943350

Up     Normal  116.44 MB       25.00%  77493140218352732093706282561390969782

Up     Normal  27.01 MB        12.68%  99065646426277998282363457251162269147

Up     Normal  35.9 MB         12.32%  120028436083470040026628108490361996214

Up     Normal  512.55 KB       25.00%  162563731948587347959549934419333022646

 

RF:2 and CL: QUORUM – writes at a rate of 1750 rows/s – every row – 5 cols and 2 of them indexes.

 

Thanks,

Dushyant

 

 

From: aaron morton [mailto:aaron@thelastpickle.com]
Sent: Monday, March 05, 2012 11:07 PM
To: user@cassandra.apache.org
Subject: Re: Mutation Dropped Messages

 

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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