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From Patrik Modesto <>
Subject Poor write performance with seconrady index
Date Mon, 16 Apr 2012 14:51:19 GMT

I've a 4 node test cluster running Cassandra 1.0.9, 32GB memory, 4x
1TB disks. I've two keyspaces, rfTest2 (RF=2) and rfTest3 (RF=3).
There are two CF, one with source data and one with secondary index:

create column family UrlGroup
    with column_type=Standard
    and comparator=UTF8Type
    and default_validation_class=UTF8Type
    and key_validation_class=UTF8Type
    and column_metadata=
        column_name: groupId,
        validation_class: UTF8Type,
        index_type: KEYS

I'm running Hadoop mapreduce job, reading the source CF and creating 3
mutations for each row-key in the UrlGroup CF.

The mapreduce runs for 30minutes. When I remove the secondary index,
the mapreduce runs just 10minutes. There are 26,273,544 mutations

Also with the secondary index, the nodes show very high load 50+ and
iowait 70%+. Without secondary index the load is ~5 and iowait ~10%.

What may be the problem?


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