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From Eran Chinthaka Withana <eran.chinth...@gmail.com>
Subject Re: Key cache hit rate issue
Date Fri, 17 Feb 2012 06:10:30 GMT
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

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