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From "Jonathan Ellis (JIRA)" <j...@apache.org>
Subject [jira] Created: (CASSANDRA-2184) Returning split length of 0 confuses Pig
Date Thu, 17 Feb 2011 18:36:24 GMT
Returning split length of 0 confuses Pig
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                 Key: CASSANDRA-2184
                 URL: https://issues.apache.org/jira/browse/CASSANDRA-2184
             Project: Cassandra
          Issue Type: Bug
          Components: Hadoop
    Affects Versions: 0.6
            Reporter: Jonathan Ellis
            Priority: Minor
             Fix For: 0.7.3


Matt Kennedy reports on the user list,

bq. There is a new feature in Pig 0.8 that will try to reduce the number of splits used to
speed up the whole job.  Since the ColumnFamilyInputFormat lists the input size as zero, this
feature eliminates all of the splits except for one. 
bq. The workaround is to disable this feature for jobs that use CassandraStorage by setting
-Dpig.splitCombination=false in the pig_cassandra script.
{noformat}

bq. However, we wanted to keep splitCombination on because it is a useful optimization for
a lot of our use cases, so I went digging for the least intrusive way to keep the split combiner
on, but also prevent it from combining splits that read from Cassandra.  My solution, which
you are welcome to critique, is to change line 65 of http://svn.apache.org/viewvc/cassandra/trunk/src/java/org/apache/cassandra/hadoop/ColumnFamilySplit.java
such that it returns Long.MAX_VALUE instead of zero.

I looked into actually returning the number of keys in the split but Hadoop javadoc says "Get
the size of the split, so that the input splits can be sorted by size" so since our splits
should be very very close in size this doesn't sound like it's worth doing an extra round
trip to the host servers to get super accurate numbers on.  Returning MAX_VALUE seems like
it's good enough.

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