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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Error reporting Key cache hit rate with cfstats or with JMX
Date Tue, 25 May 2010 12:43:32 GMT
What happens if you disable row cache?

On Tue, May 25, 2010 at 4:53 AM, Ran Tavory <rantav@gmail.com> wrote:
> It seems there's an error reporting the Key cache hit rate. The value is
> always 0.0 and I have a feeling it's incorrect. This is seen both by using
> notetool cfstats as well as accessing JMX directly
> (org.apache.cassandra.db:type=Caches,keyspace=outbrain_kvdb,cache=KvAdsKeyCache
> RecentHitRate)
>       <ColumnFamily CompareWith="BytesType" Name="KvAds"
>                     RowsCached="10000000"
>                     KeysCached="10000000"/>
>                 Column Family: KvAds
>                 SSTable count: 7
>                 Space used (live): 1288942061
>                 Space used (total): 1559831566
>                 Memtable Columns Count: 73698
>                 Memtable Data Size: 17121092
>                 Memtable Switch Count: 33
>                 Read Count: 3614433
>                 Read Latency: 0.068 ms.
>                 Write Count: 3503269
>                 Write Latency: 0.024 ms.
>                 Pending Tasks: 0
>                 Key cache capacity: 10000000
>                 Key cache size: 619624
>                 Key cache hit rate: 0.0
>                 Row cache capacity: 10000000
>                 Row cache size: 447154
>                 Row cache hit rate: 0.8460295730014572
>                 Compacted row minimum size: 387
>                 Compacted row maximum size: 31430
>                 Compacted row mean size: 631
> The Row cache hit rate looks good, 0.8 but Key cache hit rate always seems
> to be 0.0 while the number of unique keys stays about 619624 for quite a
> while.
> Is it a real caching problem or just a reporting glitch?



-- 
Jonathan Ellis
Project Chair, Apache Cassandra
co-founder of Riptano, the source for professional Cassandra support
http://riptano.com

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