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From Brandon Williams <dri...@gmail.com>
Subject Re: Cassandra benchmark shows OK throughput but high read latency (> 100ms)?
Date Tue, 16 Feb 2010 14:06:13 GMT
On Tue, Feb 16, 2010 at 2:32 AM, Dr. Martin Grabm├╝ller <
Martin.Grabmueller@eleven.de> wrote:

> In my tests I have observed that good read latency depends on keeping
> the number of data files low.  In my current test setup, I have stored
> 1.9 TB of data on a single node, which is in 21 data files, and read
> latency is between 10 and 60ms (for small reads, larger read of course
> take more time).  In earlier stages of my test, I had up to 5000
> data files, and read performance was quite bad: my configured 10-second
> RPC timeout was regularly encountered.
>

I believe it is known that crossing sstables is O(NlogN) but I'm unable to
find the ticket on this at the moment.  Perhaps Stu Hood will jump in and
enlighten me, but in any case I believe
https://issues.apache.org/jira/browse/CASSANDRA-674 will eventually solve
it.

Keeping write volume low enough that compaction can keep up is one solution,
and throwing hardware at the problem is another, if necessary.  Also, the
row caching in trunk (soon to be 0.6 we hope) helps greatly for repeat hits.

-Brandon

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