Benedict created CASSANDRA-7031:
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Summary: Increase default commit log total space + segment size
Key: CASSANDRA-7031
URL: https://issues.apache.org/jira/browse/CASSANDRA-7031
Project: Cassandra
Issue Type: Improvement
Components: Core
Reporter: Benedict
Assignee: Benedict
Priority: Trivial
Fix For: 2.1 beta2
I would like to increase the default commit log total space and segment size
options for 64-bit JVMs:
The current default of 1Gb and 32Mb is quite constrained and can have some
(very minor) negative performance implications, for no major benefit:
# 32Mb files are actually quite small, and if during the 10s interval we have
completely filled multiple of them (quite easy) it would be more efficient to
write fewer larger files, as we can issue fewer fsyncs and permit the OS to
schedule the writes more efficiently. On my box this has a small but noticeable
impact. Although I would expect on decent server hardware this would be smaller
still, since we immediately drop the pages from cache on writing there isn't a
great deal of advantage to keeping the files so small. The only advantage I can
see is that during a drop KS/CF or other event that forces log rollover we're
wasting less space until log recycling. 128-256Mb are modest increases that
seem more appropriate to me.
# 1Gb is too small for the default total log space. We can find that we force
memtable flushes as a result of log utilisation instead of memtable occupancy
quite often (esp. as a result of increased effective memtable space from recent
improvements), especially on machines with more addressable memory. I suggest
8Gb as a minimum. The only disadvantage of having more log data is that replay
on restart may be slightly slower, but since most of the events will be ignored
it should be relatively benign, and I would rather take the penalty on startup
instead of during running, no matter how small the running penalty.
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