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From Nazario Parsacala <dodongj...@gmail.com>
Subject Read latency on one ColumnFamily greater than the rest of Column Families ..
Date Fri, 11 Jun 2010 19:32:26 GMT
So I have setup some test with Cassandra (with OCM). Though not very
impressed with the single read speeds , I have observed that it does scale
very well even with numerous number of concurrent readers .. However I have
observed that no matter what I do , I am somehow limitted to around 4 ms of
read per record .. I ran cfstats and noticed that one of the ColumnFamilies
(called Application) has the exact read latency that I have .. The other
ColumnFamily seems to be very good . You can see the cfstats output below.
Any reason why ..?



    Read Count: 208678
        Read Latency: 1.0831235635764191 ms.
        Write Count: 0
        Write Latency: NaN ms.
        Pending Tasks: 0
                Column Family: Server
                SSTable count: 2
                Space used (live): 43553650
                Space used (total): 43553650
                Memtable Columns Count: 0
                Memtable Data Size: 0
                Memtable Switch Count: 0
                Read Count: 11200
                Read Latency: 0.208 ms.
                Write Count: 0
                Write Latency: NaN ms.
                Pending Tasks: 0
                Key cache capacity: 200000
                Key cache size: 1929
                Key cache hit rate: 0.8369929601072745
                Row cache: disabled
                Compacted row minimum size: 0
                Compacted row maximum size: 0
                Compacted row mean size: 0

                Column Family: Application
                SSTable count: 1
                Space used (live): 1816170
                Space used (total): 1816170
                Memtable Columns Count: 0
                Memtable Data Size: 0
                Memtable Switch Count: 0
                Read Count: 43884
                Read Latency: 4.051 ms.
                Write Count: 0
                Write Latency: NaN ms.
                Pending Tasks: 0
                Key cache capacity: 200000
                Key cache size: 361
                Key cache hit rate: 0.9917737672044481
                Row cache: disabled
                Compacted row minimum size: 0
                Compacted row maximum size: 0
                Compacted row mean size: 0

                Column Family: BusinessUnit
                SSTable count: 1
                Space used (live): 4965
                Space used (total): 4965
                Memtable Columns Count: 0
                Memtable Data Size: 0
                Memtable Switch Count: 0
                Read Count: 21942
                Read Latency: 0.104 ms.
                Write Count: 0
                Write Latency: NaN ms.
                Pending Tasks: 0
                Key cache capacity: 200000
                Key cache size: 13
                Key cache hit rate: 0.999316379546076
                Row cache: disabled
                Compacted row minimum size: 0
                Compacted row maximum size: 0
                Compacted row mean size: 0

                Column Family: Deployment
                SSTable count: 1
                Space used (live): 9694570
                Space used (total): 9694570
                Memtable Columns Count: 0
                Memtable Data Size: 0
                Memtable Switch Count: 0
                Read Count: 43884
                Read Latency: 0.526 ms.
                Write Count: 0
                Write Latency: NaN ms.
                Pending Tasks: 0
                Key cache capacity: 200000
                Key cache size: 1018
                Key cache hit rate: 0.9767796919150488
                Row cache: disabled
                Compacted row minimum size: 0
                Compacted row maximum size: 0
                Compacted row mean size: 0

                Column Family: AppFamily
                SSTable count: 1
                Space used (live): 135233
                Space used (total): 135233
                Memtable Columns Count: 0
                Memtable Data Size: 0
                Memtable Switch Count: 0
                Read Count: 43884
                Read Latency: 0.344 ms.
                Write Count: 0
                Write Latency: NaN ms.
                Pending Tasks: 0
                Key cache capacity: 200000
                Key cache size: 109
                Key cache hit rate: 0.9975161790174095
                Row cache: disabled
                Compacted row minimum size: 0
                Compacted row maximum size: 0
                Compacted row mean size: 0

                Column Family: SubBu
                SSTable count: 1
                Space used (live): 24659
                Space used (total): 24659
                Memtable Columns Count: 0
                Memtable Data Size: 0
                Memtable Switch Count: 0
                Read Count: 43884
                Read Latency: 0.125 ms.
                Write Count: 0
                Write Latency: NaN ms.
                Pending Tasks: 0
                Key cache capacity: 200000
                Key cache size: 41
                Key cache hit rate: 0.9990657187129706
                Row cache: disabled
                Compacted row minimum size: 0
                Compacted row maximum size: 0
                Compacted row mean size: 0

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