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From Teijo Holzer <thol...@wetafx.co.nz>
Subject Re: Read latency is over 1 minute on a column family with 400,000 rows
Date Mon, 01 Aug 2011 02:54:12 GMT
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
>
>
>
> --
> View this message in context: http://cassandra-user-incubator-apache-org.3065146.n2.nabble.com/Read-latency-is-over-1-minute-on-a-column-family-with-400-000-rows-tp6639649p6639649.html
> Sent from the cassandra-user@incubator.apache.org mailing list archive at Nabble.com.


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