Maintain Numeric scale when computing AVG across shards#992
Merged
Conversation
When computing this across shards, our behavior could slightly diverge from PG's. PG will maintain the scale of the column in the resulting average (or the default scale when converting a integer to a numeric). However, when we divide a Rust `Decimal`, it will potentially increase the scale and track more significant digits. If these were floats, I would argue we should ignore this and as long as our behavior is within epsilon of what vanilla PG would do that is acceptable. But numeric is a type you use specifically in order to be able to specify the scale, so returning a more precise result isn't acceptable.
sgrif
commented
May 20, 2026
| } else { | ||
| Some(Datum::Numeric(Numeric::from(decimal / divisor))) | ||
| let mut result = decimal / divisor; | ||
| result.rescale(decimal.scale()); |
Contributor
Author
There was a problem hiding this comment.
This line is the relevant change. Everything else is light cleanup
Codecov Report❌ Patch coverage is
📢 Thoughts on this report? Let us know! |
Collaborator
|
The LB test is flaky. |
Contributor
|
Found 1 test failure on Blacksmith runners: Failure
|
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
2 participants
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
When computing this across shards, our behavior could slightly diverge from PG's. PG will maintain the scale of the column in the resulting average (or the default scale when converting a integer to a numeric). However, when we divide a Rust
Decimal, it will potentially increase the scale and track more significant digits.If these were floats, I would argue we should ignore this and as long as our behavior is within epsilon of what vanilla PG would do that is acceptable. But numeric is a type you use specifically in order to be able to specify the scale, so returning a more precise result isn't acceptable.