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From "Rick Hillegas (JIRA)" <j...@apache.org>
Subject [jira] [Created] (DERBY-6127) Tell users to make sure that the state of a user-defined aggregate needs to be serializable
Date Fri, 22 Mar 2013 14:23:15 GMT
Rick Hillegas created DERBY-6127:
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             Summary: Tell users to make sure that the state of a user-defined aggregate needs
to be serializable
                 Key: DERBY-6127
                 URL: https://issues.apache.org/jira/browse/DERBY-6127
             Project: Derby
          Issue Type: Improvement
          Components: Documentation
    Affects Versions: 10.10.1.1
            Reporter: Rick Hillegas


The Reference Manual section on "CREATE DERBY AGGREGATE statement" should tell users to make
sure that all of the state of their user-defined aggregate is really serializable. This is
because the Aggregator interface extends java.io.Serializable. A user-defined aggregate may
end up being serialized to disk when performing grouped aggregation over a large number of
groups. That is, intermediate results may be serialized to disk for a query like the following.
The serialization will fail if the user-defined aggregate contains non-serializable fields:

  select a, myAggregate( b ) from myTable group by a

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