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From Jonathan Ellis <>
Subject Re: Cassandra benchmark shows OK throughput but high read latency (> 100ms)?
Date Wed, 17 Feb 2010 01:34:27 GMT
On Tue, Feb 16, 2010 at 7:27 PM, Weijun Li <> wrote:
> Yes my KeysCachedFraction is already 0.3 but it doesn't relief the disk i/o.
> I compacted the data to be a 60GB (took quite a while to finish and it
> increased latency as expected) one but doesn't help much either.
> If I set KCF to 1 (meaning to cache all sstable index), how much memory will
> it take for 50mil keys?

10/3 what 0.3 takes :)

>Is the index a straight key-offset map? I guess key
> is 16 bytes and offset is 8 bytes.

key length depends on your data, of course.

> Will KCF=1 help to reduce disk i/o?

depends.  w/ trunk you can look at your cache hit rate w/ jconsole to
see if increasing it more would help.


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