[DERBY-6127] Tell users to make sure that the state of a user-defined aggregate needs to be serializable

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 10.10.1.1
• Fix Version/s: 10.10.2.0, 10.11.1.1
• Component/s: Documentation
• Assignee: Camilla Haase
• Reporter: Richard N. Hillegas
• Created: 22/Mar/13 14:22
• Updated: 16/Apr/14 02:41
• Resolved: 12/Sep/13 22:23

Description

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

Issue Links

• relates to: DERBY-672 Re-enable user defined aggregates