2010YOUY01 commented on PR #26227:
URL: https://github.com/apache/datafusion/pull/26227#issuecomment-6394732608
@jayzhan211 Thank you for the review
> @2010YOUY01 On the coverage question: the feature-freeze plan sounds good
to me, but once this merges nothing runs with `enable_migration_hash_join =
false` for inner/left/right/full joins, and that's the setting users would fall
back to if the new path has a bug. #22729 handled the same problem by
randomizing `enable_migration_aggregate` in the aggregation fuzzer. Doing the
same in `run_test` in `join_fuzz.rs` is only a few lines, and it's fine as a
follow-up:
>
> ```rust
> for (i, batch_size) in self.batch_sizes.iter().enumerate() {
> let mut session_config =
SessionConfig::new().with_batch_size(*batch_size);
> // Keep the legacy path covered until it is removed (#26361)
> session_config
> .options_mut()
> .execution
> .enable_migration_hash_join = i % 2 == 0;
> ```
Addressed in
[4b20989](https://github.com/apache/datafusion/pull/26227/commits/4b20989d13ef494a573a16efe4751472327853c4),
and also added several `enable_migration_hash_join = false/true` config matrix
in major slts.
I agree we can keep them. It's only 20 LoC in total, and easy to add/revert.
As explained above in the 'feature-freeze' approach, leaving the old impl
untested is probably okay, since it should remain stable if we don't change it.
However, I think changes in other components might propagate to the old HJ impl
and cause some bugs to surface.
I think this approach cheaply preserves most of the test coverage for extra
assurance. Some UTs won't run on the old impl, but that should be acceptable
given the 'feature-freeze' assumption.
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