Most likely compaction kicks in as updates cause duplicated rows in STCS and compaction causes load that may not have been there before(check your logs). Also, you can increase the number of nodes in your cluster as well to better handle the load.
Later, Dean From: Jay Svc <jaytechg...@gmail.com<mailto:jaytechg...@gmail.com>> Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>> Date: Tuesday, March 26, 2013 5:05 PM To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>> Subject: Insert v/s Update performance Hi Team, I have this 3 node cluster. I am writing data to these node at the rate of 2,000 records/second. What I observed that if I do inserts. (Means records for those keys does not exist, my column family has 0 records to start with) then I have better write performacne, low SSTable count, low pending compaction and write latency is acceptable and CPU utilization on each node between 35% to 85%. When I ran same test but for update this time (means records already exists in Column family with same key), I observed that my SSTable count gone high 3 times. Pending compactions gone high more than 2 times and write latency has gone high too and CPU utilization was almost 92% to 100%. What is a reason of deteriorating Update performance v/s Insert performance. Since this is critical you help is highly appriciated. P.S. I also observed that high number of pending Mutation Stage on my nodetool tpstats. Thanks, Jay
