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Posted to github@arrow.apache.org by "mustafasrepo (via GitHub)" <gi...@apache.org> on 2023/11/14 11:50:38 UTC
[PR] Preserve all of the valid orderings during merging. [arrow-datafusion]
mustafasrepo opened a new pull request, #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169
## Which issue does this PR close?
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## Rationale for this change
Currently during merging (`SortPreservingMergeExec`) we can only preserve single ordering of the one of the valid orderings of the table.
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Re: [PR] Preserve all of the valid orderings during merging. [arrow-datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on PR #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169#issuecomment-1811540241
Thank you @mustafasrepo -- this is very neat
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Re: [PR] Preserve all of the valid orderings during merging. [arrow-datafusion]
Posted by "tustvold (via GitHub)" <gi...@apache.org>.
tustvold commented on PR #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169#issuecomment-1812155562
This PR appears to have broken logic merge conflicts that have broken CI - https://github.com/apache/arrow-datafusion/pull/8186
@ozankabak could you take a look?
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Re: [PR] Preserve all of the valid orderings during merging. [arrow-datafusion]
Posted by "ozankabak (via GitHub)" <gi...@apache.org>.
ozankabak commented on code in PR #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169#discussion_r1392506421
##########
datafusion/physical-expr/src/equivalence.rs:
##########
@@ -575,10 +588,19 @@ impl OrderingEquivalenceClass {
}
}
- /// Gets the first ordering entry in this ordering equivalence class.
- /// This is one of the many valid orderings (if there are multiple).
+ /// Gets the concatenated version of the all orderings.
+ /// if orderings are [a ASC, b ASC] and [c ASC, d ASC]
+ /// Returns [a ASC, b ASC, c ASC, d ASC].
+ /// This ensures that during during merging
+ /// [a ASC, b ASC] and [c ASC, d ASC] are still valid.
pub fn output_ordering(&self) -> Option<LexOrdering> {
- self.orderings.first().cloned()
+ let output_ordering = self
+ .orderings
+ .iter()
+ .flat_map(|ordering| ordering.to_vec())
+ .collect::<Vec<_>>();
Review Comment:
Nit: We can probably write this more idiomatically and avoid collecting individual pieces.
##########
datafusion/physical-expr/src/equivalence.rs:
##########
@@ -575,10 +588,19 @@ impl OrderingEquivalenceClass {
}
}
- /// Gets the first ordering entry in this ordering equivalence class.
- /// This is one of the many valid orderings (if there are multiple).
+ /// Gets the concatenated version of the all orderings.
+ /// if orderings are [a ASC, b ASC] and [c ASC, d ASC]
+ /// Returns [a ASC, b ASC, c ASC, d ASC].
+ /// This ensures that during during merging
+ /// [a ASC, b ASC] and [c ASC, d ASC] are still valid.
Review Comment:
```suggestion
/// Returns the concatenation of all the orderings. This enables merge
/// operations to preserve all equivalent orderings simultaneously.
```
##########
datafusion/physical-plan/src/repartition/mod.rs:
##########
@@ -472,9 +472,6 @@ impl ExecutionPlan for RepartitionExec {
if !self.maintains_input_order()[0] {
result.clear_orderings();
}
- if self.preserve_order {
- result = result.with_reorder(self.sort_exprs().unwrap_or_default().to_vec())
- }
Review Comment:
For other reviewers: This is the key change that avoids losing alternative orderings.
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Re: [PR] Preserve all of the valid orderings during merging. [arrow-datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on code in PR #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169#discussion_r1393420890
##########
datafusion/physical-expr/src/equivalence.rs:
##########
@@ -575,10 +588,13 @@ impl OrderingEquivalenceClass {
}
}
- /// Gets the first ordering entry in this ordering equivalence class.
- /// This is one of the many valid orderings (if there are multiple).
+ /// Returns the concatenation of all the orderings. This enables merge
+ /// operations to preserve all equivalent orderings simultaneously.
pub fn output_ordering(&self) -> Option<LexOrdering> {
- self.orderings.first().cloned()
+ let output_ordering =
+ self.orderings.iter().flatten().cloned().collect::<Vec<_>>();
+ let output_ordering = collapse_lex_ordering(output_ordering);
Review Comment:
this is another core change, right? It preserves all the possible orderings
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Re: [PR] Preserve all of the valid orderings during merging. [arrow-datafusion]
Posted by "mustafasrepo (via GitHub)" <gi...@apache.org>.
mustafasrepo commented on code in PR #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169#discussion_r1393660010
##########
datafusion/physical-expr/src/equivalence.rs:
##########
@@ -575,10 +588,13 @@ impl OrderingEquivalenceClass {
}
}
- /// Gets the first ordering entry in this ordering equivalence class.
- /// This is one of the many valid orderings (if there are multiple).
+ /// Returns the concatenation of all the orderings. This enables merge
+ /// operations to preserve all equivalent orderings simultaneously.
pub fn output_ordering(&self) -> Option<LexOrdering> {
- self.orderings.first().cloned()
+ let output_ordering =
+ self.orderings.iter().flatten().cloned().collect::<Vec<_>>();
+ let output_ordering = collapse_lex_ordering(output_ordering);
Review Comment:
Yes, this is the place where we concatenate all valid orderings so that they can be preserved during merge
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Re: [PR] Preserve all of the valid orderings during merging. [arrow-datafusion]
Posted by "ozankabak (via GitHub)" <gi...@apache.org>.
ozankabak merged PR #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169
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Re: [PR] Preserve all of the valid orderings during merging. [arrow-datafusion]
Posted by "ozankabak (via GitHub)" <gi...@apache.org>.
ozankabak commented on PR #8169:
URL: https://github.com/apache/arrow-datafusion/pull/8169#issuecomment-1811976465
Thanks @alamb, I will go ahead and merge this then. If you encounter any issue related to this, please let us know so we can promptly fix it
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