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From Jiaan Zeng <>
Subject unstable write performance
Date Wed, 26 Mar 2014 14:54:39 GMT

I am doing some performance benchmarks in a *single* node cassandra
1.2.4. BTW, the machine is dedicated to run one cassandra instance.
The workload is 100% write. The throughput varies dramatically and
sometimes even drops to 0. I have tried several things below and still
got the same observation. There is no errors in the log file. One
thing I spotted in the log is GCInspector reports GC takes more than
200 ms. I think that is because the size of the memtable setting. If I
lower the memtable size, that kind of report can go away. Any clues
about what is happening in this case and suggestions about how to
achieve a stable write throughput? Thanks a lot.

1) Increase heap size from 4 G to 8 G. The total memory is 16 G.
2) Increase "memtable_total_space_in_mb" and
"commitlog_total_space_in_mb" to decrease the number of memtable
3) Disable the compaction to eliminate the impact of compaction on disk.

Below is an example of throughput.
280 sec: 865658 operations; 2661.5 current ops/sec; [INSERT
 290 sec: 865658 operations; 0 current ops/sec;
 300 sec: 903204 operations; 3754.22 current ops/sec; [INSERT


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