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satvantsingh_190085 avatar image
satvantsingh_190085 asked ·

What is mutations in Cassandra and how do they affect cluster performance?

Could you please explain what is mutation in Cassandra . What is missed mutations , dropped mutations etc.

cassandra
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1 Answer

Erick Ramirez avatar image
Erick Ramirez answered ·

"Mutations" is just another word for database "writes". They are INSERT, UPDATE and DELETE statements from the application. The word "mutation" is used because these statements change the data in the database.

Mutations are dropped when a node's commitlog disk cannot keep up with the write requests being sent to it. The write operation in this case is "missed" and considered a failure by the coordinator node.

When you see dropped mutations in the logs, review the performance of the commitlog disk using Linux utilities such as iostat or fio (flexible I/O tester). If you have server and cluster monitoring in place, check the graph of write requests over the last week or last month. It will usually show that the IO traffic to the cluster is either growing constantly or spiking which would explain why the disk cannot keep up with IO requests.

For more info, see How data is written in Cassandra and Thread pool statistics recommendations. Cheers!

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