[BEAM-6906] Mutating accumulators in fused stages is generally unsafe - need to provide a single mutable accumulator

• Type: Bug
• Status: Resolved
• Priority: P1
• Resolution: Fixed
• Fix Version/s: 2.13.0
• Component/s: beam-model
• Assignee: Robin Qiu
• Reporter: Kenneth Knowles
• Created: 25/Mar/19 21:51
• Updated: 13/Mar/21 03:34
• Resolved: 13/Mar/21 03:34

Description

Our current docs encourage a CombineFn author to mutate accumulators for efficiency. This is important, but cannot be done generally without losing efficiency - it is not safe to share accumulators within a stage or across sliding windows. The ownership story needs to be clear. Any accumulator that is mutable is from that point on owned by the CombineFn, not the runner and cannot be given to other steps.

Issue Links

• links to: GitHub Pull Request #8134