Decimal division compatibility mode with spark
- Dominant language
- Rust
- Stars
- 9.3k
- Forks
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- Avg merge
- 3d 7h
- Merged PRs (30d)
- 344
Description
### Is your feature request related to a problem or challenge?
As described in detail by @liukun4515 and @tustvold and @viirya on https://github.com/apache/arrow-datafusion/pull/6832, DataFusion's decimal devision semantics.
@liukun4515 notes https://github.com/apache/arrow-datafusion/pull/6832#issuecomment-1680098056 that spark has the config to control the precision loss : https://github.com/apache/spark/blob/2be20e54a2222f6cdf64e8486d1910133b43665f/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/expressions/arithmetic.scala#L246
And @tustvold notes For people looking to emulate spark which only supports precision up to 38, casting to Decimal256 and then truncating down to Decimal128 will be equivalent, and is what a precision loss arithmetic kernel would do
### Describe the solution you'd like
If anyone needs spark compatible decimal division rules, I suggest:
1. Add a new config option
2. Apply the rewrite suggested by @tustvold (cast to Decimal256, divide, and then cast to Decimal128) as an [AnalyzerRule](https://docs.rs/datafusion/latest/datafusion/optimizer/analyzer/trait.AnalyzerRule.html#)
### Describe alternatives you've considered
See ticket -- we discussed at length changing the semantics of division in arrow-rs and concluded there was no one agreed upon ideal behavior
### Additional context
_No response_
Contributor guide
Research direction
Start with the discussion in pull request 6832 and the AnalyzerRule documentation linked in the issue. Trace how decimal division is analyzed, then determine where a new configuration option and the Decimal256-to-Decimal128 rewrite belong. Done means Spark-compatible decimal division behavior is covered by tests, though no test file is named in the issue.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust, spark, sql
- Domain
- backend, databases
- Issue type
- Feature
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 35/100