apache / apache/datafusion

`NestedLoopsJoin` memory tracking may be insufficient

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enhancement
Dominant language
Rust
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Merged PRs (30d)
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Description

### Is your feature request related to a problem or challenge?

Similarly to https://github.com/apache/arrow-datafusion/issues/7848, @metesynnada noted https://github.com/apache/arrow-datafusion/pull/8020#issuecomment-1903359773 that it is possible for `NestedLoopsJoin` to generate a single (very) large `RecordBatch`. For certain pathalogical queries this may lead to DataFusion far exceeding its memory limits and erroring out

### Describe the solution you'd like

Implement / adapt the same approach as @korowa did in https://github.com/apache/arrow-datafusion/pull/8020 (❤️ ) to incrementally create join output for joins that match many keys rather than doing it all at once.

### Describe alternatives you've considered

_No response_

### Additional context

_No response_

Contributor guide

Open the contributing guide

Research direction

Start by reading the related issue 7848 and pull request 8020, especially the approach for incrementally producing join output. Then trace NestedLoopsJoin to identify where many matching keys create one large RecordBatch; done means join output is produced incrementally without exceeding configured memory limits for pathological queries.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
databases
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
38/100

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