Re: Read latency is over 1 minute on a column family with 400,000 rows

[Teijo Holzer]

Hi,

try running a major compaction via nodetool on this Column family. The number 
of SSTables seems quite large.

Considering the space used, this might take a few hours and might also impact 
performance.

Cheers,

        T.

On 01/08/11 14:23, myreasoner wrote:
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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