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From myreasoner <myreaso...@gmail.com>
Subject Read latency is over 1 minute on a column family with 400,000 rows
Date Mon, 01 Aug 2011 02:23:02 GMT
Hi, my read latency is really horrible and I can't figure out what went
wrong.  I'm running cassandra 0.8.0 on a 5 machine cluster.  The Fingerprint
ColumnFamily has 400,000 rows, each row has about 4,000 Super columns, and
each super column has 1 to 4 columns.  One row looks like:

RowKey: 00c26f
=> (super_column=008002c161f008566a4931d6efeab128ef,
     (column=183e9d10-b5f0-11e0-b0f4-0025901867fb, value=,
timestamp=1311510352604000))
=> (super_column=008004c34cafa12e22acbf3c2aab9b15ef,
     (column=e6371bf6-b72c-11e0-b201-0025901867fb, value=,
timestamp=1311646419206000)
     (column=e6371c00-b72c-11e0-b201-0025901867fb, value=,
timestamp=1311646419206000))
=> (super_column=0080097ac5154a96ea8620784ea3b5b56f,
     (column=7691b846-b6fc-11e0-a703-003048f330bb, value=,
timestamp=1311625615955000))
...


On cassandra-cli doing *get Fingerprint[rowkey][SuperColumnName]* usually
takes over 60 seconds to return, which almost make the read un-useable.  Is
there anything I can tune?
 
Here are the stats for a column family Fingerprint.
                Column Family: Fingerprint
                SSTable count: 2056
                Space used (live): 164074936666
                Space used (total): 164074936666
                Memtable Columns Count: 177451
                Memtable Data Size: 119948171
                Memtable Switch Count: 366
                Read Count: 5
                *Read Latency: 74487.252 ms.*
                Write Count: 30023
                Write Latency: 1.602 ms.
                Pending Tasks: 0
                Key cache capacity: 200000
                Key cache size: 8157
                Key cache hit rate: 0.01322228263555929
                Row cache: disabled
                Compacted row minimum size: 104
                Compacted row maximum size: 315852
                Compacted row mean size: 33709



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