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Posted to commits@beam.apache.org by "Eugene Kirpichov (JIRA)" <ji...@apache.org> on 2018/01/06 19:49:03 UTC

[jira] [Created] (BEAM-3424) CassandraIO uses 1 split if can't estimate size

Eugene Kirpichov created BEAM-3424:
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             Summary: CassandraIO uses 1 split if can't estimate size
                 Key: BEAM-3424
                 URL: https://issues.apache.org/jira/browse/BEAM-3424
             Project: Beam
          Issue Type: Bug
          Components: sdk-java-extensions
            Reporter: Eugene Kirpichov
            Assignee: Jean-Baptiste Onofré


See https://stackoverflow.com/questions/48090668/how-to-increase-dataflow-read-parallelism-from-cassandra?noredirect=1#comment83227824_48090668 . When CassandraIO can't estimate size, it falls back to a single split:

https://github.com/apache/beam/blob/master/sdks/java/io/cassandra/src/main/java/org/apache/beam/sdk/io/cassandra/CassandraServiceImpl.java#L196

A single split is very poor for performance. We should fall back to a different value. Not sure what a good value would be; probably the largest value that still doesn't introduce too much per-split overhead? E.g. would there be any downside to just changing that number to 100?

Alternatively/additionally, like in DatastoreIO, CassandraIO could accept requested number of splits as a parameter.



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