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https://issues.apache.org/jira/browse/DERBY-6127?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13765398#comment-13765398
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Kim Haase commented on DERBY-6127:
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Thanks, Rick!
Since it is the UDA that actually performs the aggregation, it looks like the
sentence should read something like, "A user-defined aggregate may be
serialized to disk when it performs grouped aggregation ..."
Would that work?
> 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
> Assignee: Kim Haase
>
> 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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