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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Key cache hit rate issue
Date Fri, 17 Feb 2012 19:30:31 GMT
Only thing I can think of is that if you've set the cache size
manually over JMX it will preserve that size if you change it via a
schema update.

On Fri, Feb 17, 2012 at 12:10 AM, Eran Chinthaka Withana
<eran.chinthaka@gmail.com> wrote:
> Hi Jonathan,
>>
>>
>> > For some reason 16637958 (the keys cached) has become a golden number
>> > and I
>> > don't see key cache increasing beyond that.
>>
>> 16637958 is your configured cache capacity according to the cfstats you
>> pasted.
>
>
> this is another weird part. If you look at the schema[1] (pasted here,
> extracted through cli), the keys_cached is set to 40million. And cfstats
> shows that cassandra is only using 16 million.
>
> Please note that I enabled row cache since I posted the cfstats. And pasting
> the latest cfstats[2] herewith.
>
> [1]
> create column family YY
>   with column_type = 'Standard'
>   and comparator = 'UTF8Type'
>   and default_validation_class = 'UTF8Type'
>   and key_validation_class = 'LongType'
>   and rows_cached = 10000.0
>   and row_cache_save_period = 0
>   and row_cache_keys_to_save = 2147483647
>   and keys_cached = 4.0E7
>   and key_cache_save_period = 14400
>   and read_repair_chance = 0.1
>   and gc_grace = 864000
>   and min_compaction_threshold = 4
>   and max_compaction_threshold = 32
>   and replicate_on_write = true
>   and row_cache_provider = 'SerializingCacheProvider'
>   and compaction_strategy =
> 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy'
>   and compression_options = {'chunk_length_kb' : '64', 'sstable_compression'
> : 'org.apache.cassandra.io.compress.SnappyCompressor'};
>
> [2]
> Keyspace: XXXXX
> Read Count: 590667
> Read Latency: 11.644107261790484 ms.
> Write Count: 12720068
> Write Latency: 0.06049896832312532 ms.
> Pending Tasks: 0
> Column Family: YY
> SSTable count: 12
> Space used (live): 66300297338
> Space used (total): 66300297338
> Number of Keys (estimate): 61152896
> Memtable Columns Count: 881972
> Memtable Data Size: 211749842
> Memtable Switch Count: 267
> Read Count: 590667
> Read Latency: 16.859 ms.
> Write Count: 12720068
> Write Latency: 0.060 ms.
> Pending Tasks: 0
> Bloom Filter False Postives: 507
> Bloom Filter False Ratio: 0.00099
> Bloom Filter Space Used: 168118968
> Key cache capacity: 40000000
> Key cache size: 3838755
> Key cache hit rate: 0.2072072072072072
> Row cache capacity: 10000
> Row cache size: 10000
> Row cache hit rate: 0.022222222222222223
> Compacted row minimum size: 51
> Compacted row maximum size: 6866
> Compacted row mean size: 2577
>
> Thanks,
> Eran



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

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