Ismaël Mejía reassigned BEAM-3424:

    Assignee: Alexander Dejanovski  (was: Alexey Romanenko)

> 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: io-java-cassandra
>            Reporter: Eugene Kirpichov
>            Assignee: Alexander Dejanovski
>            Priority: Major
> 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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