[FLINK-864] Add description of mutable object iterators (GroupReduce, CoGroup) to documentation

• Type: Sub-task
• Status: Resolved
• Priority: Major
• Resolution: Invalid
• Fix Version/s: pre-apache
• Component/s: Documentation
• Labels: github-import
• Assignee: Unassigned
• Reporter: GitHub Import
• Created: 09/Jun/14 13:03
• Updated: 04/Jun/15 16:41
• Resolved: 04/Jun/15 16:41

Description

Stratosphere uses value iterators with mutable objects.
If this is not considered by an UDF, this silently leads to invalid results and hard to debug bugs.

We had a lot of discussions about this. In the long run, we want to offer a safe default iterator which returns new objects with every call and a more efficient iterator with mutable object.

Until then, we should add a warning to the Java Docs of `GroupReduceFunction` and `CoGroupFunction`.

---------------- Imported from GitHub ----------------
Url: https://github.com/stratosphere/stratosphere/issues/864
Created by: fhueske
Labels: documentation, user satisfaction,
Milestone: Release 0.5.1
Created at: Mon May 26 10:33:28 CEST 2014
State: open

Issue Links

• is related to: FLINK-1565 Document object reuse behavior
• relates to: FLINK-1005 Add different mutable-object modes to runtime