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From Dan Kuebrich <dan.kuebr...@gmail.com>
Subject read latency in cassandra
Date Fri, 04 Feb 2011 19:13:55 GMT
Hi all,

It often takes more than two seconds to load:

- one row of ~450 events comprising ~600k
- cluster size of 1
- client is pycassa 1.04
- timeout on recv
- cold read (I believe)
- load generally < 0.5 on a 4-core machine, 2 EC2 instance store drives for
cassandra
- cpu wait generally < 1%

Often the following sequence occurs:

1. First attempt times out after 2 sec
2. Second attempt loads fine on immediate retry

So, I assume it's an issue about cache miss and going to disk.  Is 2 seconds
the normal "I went to disk" latency for cassandra?  What should we look to
tune, if anything? I don't think keeping everything in-memory is an option
for us given dataset size and access pattern (hot set is stuff being
currently written, stuff being accessed is likely to be older).

I didn't notice this problem with cassandra 0.6.8 and pycassa 0.3.

Thanks,
dan

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