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Posted to github@datafusion.apache.org by "2010YOUY01 (via GitHub)" <gi...@apache.org> on 2025/10/20 04:54:16 UTC

[PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

2010YOUY01 opened a new pull request, #18161:
URL: https://github.com/apache/datafusion/pull/18161

   ## Which issue does this PR close?
   
   <!--
   We generally require a GitHub issue to be filed for all bug fixes and enhancements and this helps us generate change logs for our releases. You can link an issue to this PR using the GitHub syntax. For example `Closes #123` indicates that this PR will close issue #123.
   -->
   
   https://github.com/apache/datafusion/issues/18070
   
   ## Rationale for this change
   
   <!--
    Why are you proposing this change? If this is already explained clearly in the issue then this section is not needed.
    Explaining clearly why changes are proposed helps reviewers understand your changes and offer better suggestions for fixes.  
   -->
   See the above issue and its comment https://github.com/apache/datafusion/issues/18070#issuecomment-3419730649
   
   ## What changes are included in this PR?
   
   <!--
   There is no need to duplicate the description in the issue here but it is sometimes worth providing a summary of the individual changes in this PR.
   -->
   In nested loop join, when the join column includes `List(Utf8View)`, use `take()` instead of `to_array_of_size()` to avoid deep copying the utf8 buffers inside `Utf8View` array.
   
   This is the quick fix, avoiding deep copy inside `to_array_of_size()` is a bit tricky.
   Here is `ListArray`'s physical layout: https://arrow.apache.org/rust/arrow/array/struct.GenericListArray.html
   If multiple elements is pointing to the same list range, the underlying payload can't be reused.So the potential fix in `to_array_of_size` can only avoids copying the inner-inner utf8view array buffers, but can't avoid copying the inner array (i.e. views are still copied), and deep copying for other primitive types also can't be avoided. Seems this can be better solved when `ListView` type is ready 🤔 
   
   ### Benchmark
   I tried query 1 in https://github.com/apache/datafusion/issues/18070
   49.0.0: 4s
   PR: 4s
   
   Now the performance are similar, I suspect the most time is spend evaluating the expensive `array_has` so the optimization in https://github.com/apache/datafusion/pull/16996 can't help much.
   
   ## Are these changes tested?
   
   <!--
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   2. Serve as another way to document the expected behavior of the code
   
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   Existing tests
   ## Are there any user-facing changes?
   
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   No
   <!--
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Re: [PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on code in PR #18161:
URL: https://github.com/apache/datafusion/pull/18161#discussion_r2445283150


##########
datafusion/sqllogictest/test_files/join_lists.slt:
##########
@@ -0,0 +1,63 @@
+# Licensed to the Apache Software Foundation (ASF) under one

Review Comment:
    new test added here



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Re: [PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on code in PR #18161:
URL: https://github.com/apache/datafusion/pull/18161#discussion_r2445113736


##########
datafusion/physical-plan/src/joins/nested_loop_join.rs:
##########
@@ -1661,11 +1665,30 @@ fn build_row_join_batch(
             // Broadcast the single build-side row to match the filtered
             // probe-side batch length
             let original_left_array = build_side_batch.column(column_index.index);
-            let scalar_value = ScalarValue::try_from_array(
-                original_left_array.as_ref(),
-                build_side_index,
-            )?;
-            scalar_value.to_array_of_size(filtered_probe_batch.num_rows())?
+            // Avoid using `ScalarValue::to_array_of_size()` for `List(Utf8View)` to avoid
+            // deep copies for buffers inside `Utf8View` array. See below for details.
+            // https://github.com/apache/datafusion/issues/18159
+            //
+            // In other cases, `to_array_of_size()` is faster.
+            match original_left_array.data_type() {
+                DataType::List(field) | DataType::LargeList(field)
+                    if field.data_type() == &DataType::Utf8View =>
+                {
+                    let indices_iter = std::iter::repeat_n(
+                        build_side_index as u64,
+                        filtered_probe_batch.num_rows(),
+                    );
+                    let indices_array = UInt64Array::from_iter_values(indices_iter);
+                    take(original_left_array.as_ref(), &indices_array, None)?
+                }

Review Comment:
   I think this approach could be ported into `ScalarValue::to_array_of_size` itself rather than special cased here -- which would improve performance in potentially other places
   
   https://github.com/apache/datafusion/blob/556eb9b1efa7d57b95538e2178475b2a216fa497/datafusion/common/src/scalar/mod.rs#L3238-L3245
   
   That being said, I think this is a nice point fix that we can safely backport to the datafusion 50 branch, so I think we should merge this PR / backport it and I will file a follow on PR to further improve the code



##########
datafusion/physical-plan/src/joins/nested_loop_join.rs:
##########
@@ -1661,11 +1665,30 @@ fn build_row_join_batch(
             // Broadcast the single build-side row to match the filtered
             // probe-side batch length
             let original_left_array = build_side_batch.column(column_index.index);
-            let scalar_value = ScalarValue::try_from_array(
-                original_left_array.as_ref(),
-                build_side_index,
-            )?;
-            scalar_value.to_array_of_size(filtered_probe_batch.num_rows())?
+            // Avoid using `ScalarValue::to_array_of_size()` for `List(Utf8View)` to avoid
+            // deep copies for buffers inside `Utf8View` array. See below for details.
+            // https://github.com/apache/datafusion/issues/18159

Review Comment:
   The root cause is tracked in 
   - https://github.com/apache/arrow-rs/issues/6408
   



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Re: [PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on PR #18161:
URL: https://github.com/apache/datafusion/pull/18161#issuecomment-3422339655

   THANK YOU very much for this fix and diagnosis @2010YOUY01 


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Re: [PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on PR #18161:
URL: https://github.com/apache/datafusion/pull/18161#issuecomment-3422597170

   Backport PR:
   - https://github.com/apache/datafusion/pull/18179


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Re: [PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on PR #18161:
URL: https://github.com/apache/datafusion/pull/18161#issuecomment-3422462415

   
   Thank you @2010YOUY01 
   
   I just pushed a test that adds coverage for this case
   
   I verified it is covered using
   ```
   $ cargo llvm-cov test --html --profile=ci --test sqllogictests -- join_lists
   ```


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Re: [PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on PR #18161:
URL: https://github.com/apache/datafusion/pull/18161#issuecomment-3422811028

   Filed a ticket to track making `array_has` faster:
   - https://github.com/apache/datafusion/issues/18181


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Re: [PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb merged PR #18161:
URL: https://github.com/apache/datafusion/pull/18161


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Re: [PR] perf: Fix NLJ slow join with condition `array_has` [datafusion]

Posted by "2010YOUY01 (via GitHub)" <gi...@apache.org>.
2010YOUY01 commented on PR #18161:
URL: https://github.com/apache/datafusion/pull/18161#issuecomment-3422410360

   > THANK YOU very much for this fix and diagnosis @2010YOUY01
   
   Thank you for the review. The feedback makes sense to me, but I can only address it tomorrow. If you're waiting on this patch to be included in the release, feel free to push changes directly to the PR.


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