HIVE-28488: Merge multiple adjacent union distinct into single adjacent union distinct #5423
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Sep 14, 2024
| Object... nodeOutputs) throws SemanticException { | ||
| UnionMergeContext context = (UnionMergeContext) procCtx; | ||
| Collection<Operator> allOps = context.pCtx.getAllOps(); | ||
| for (int i = 1; i <= 8; i ++) { |
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could we please add some comments around this magic indices
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Added some comments to explain the meaning of indices and logic around them.
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What changes were proposed in this pull request?
This PR proposed a new optimization to reduce the shuffle when computing union distinct of multiple tables. The new optimization merges GroupBy operators computing distinct after Union, thus reducing the number of edges involved by UNION DISTINCT.
A new configuration key,
hive.optimize.merge.adjacent.union.distinct, is introduced to configure this optimization.Please check out the attached slides in the JIRA page (HIVE-28488) for further explanations.
Why are the changes needed?
To improve execution time of query containing many
UNION DISTINCT.Does this PR introduce any user-facing change?
No
Is the change a dependency upgrade?
No
How was this patch tested?
The proposed optimization is tested by running TPC-DS query 49 and 75. This PR contains a qfile test to confirm that the patch optimizes query plan.