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Posted to github@datafusion.apache.org by "ctsk (via GitHub)" <gi...@apache.org> on 2025/03/28 14:28:50 UTC
[I] Idea: Avoid planning CoalesceBatches in front of blocking operators. [datafusion]
ctsk opened a new issue, #15478:
URL: https://github.com/apache/datafusion/issues/15478
The blocking operators (HJ buid side, Aggregation) are often planned on top of a RepartitionExec with a CoalesceBatchesExec in-between. However, one of the first things these operators do is concatenate the freshly coalesced batches - Maybe there is no benefit from adding the coalesce's here?
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Re: [I] Idea: Avoid planning CoalesceBatches in front of blocking operators. [datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb commented on issue #15478:
URL: https://github.com/apache/datafusion/issues/15478#issuecomment-3716322677
We have now removed the operator entirely via
- https://github.com/apache/datafusion/issues/19591
And we have incorporated the coalescing in the relevant operators)
So I think this issue is now complete
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Re: [I] Idea: Avoid planning CoalesceBatches in front of blocking operators. [datafusion]
Posted by "ctsk (via GitHub)" <gi...@apache.org>.
ctsk commented on issue #15478:
URL: https://github.com/apache/datafusion/issues/15478#issuecomment-2761947061
One downside: Increased memory usage.
The hash join build side stores the RecordBatches in a vector before building the hash table. This vector will grow larger. In addition, we might delay e.g. garbage collection for StringViews, which also increases memory usage.
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Re: [I] Idea: Avoid planning CoalesceBatches in front of blocking operators. [datafusion]
Posted by "Dandandan (via GitHub)" <gi...@apache.org>.
Dandandan commented on issue #15478:
URL: https://github.com/apache/datafusion/issues/15478#issuecomment-2762997345
> One downside: Increased memory usage.
>
> The hash join build side stores the RecordBatches in a vector before building the hash table. This vector will grow larger. In addition, we might delay e.g. garbage collection for StringViews, which also increases memory usage.
Perhaps instead of removing the coalescebatches, we can change the the threshold ratio to be much smaller (e.g. 1/10th (or something based on some benchmarkig) of the size instead of 1/2). That way the overhead of `Vec` is minimal while probably still redundant copying in many cases.
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Re: [I] Idea: Avoid planning CoalesceBatches in front of blocking operators. [datafusion]
Posted by "alamb (via GitHub)" <gi...@apache.org>.
alamb closed issue #15478: Idea: Avoid planning CoalesceBatches in front of blocking operators.
URL: https://github.com/apache/datafusion/issues/15478
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