[ARROW-16562] [C++] Avoid slicing array inputs in ExecBatchIterator that would result in one slice

• Type: Sub-task
• Status: Closed
• Priority: Minor
• Resolution: Won't Fix
• Component/s: C++
• Labels: pull-request-available
• External issue URL: https://github.com/apache/arrow/issues/31921
• Assignee: Tobias Zagorni
• Reporter: Tobias Zagorni
• Created: 12/May/22 21:24
• Updated: 11/Jan/23 11:44
• Resolved: 13/Jun/22 13:29

Description

For scalar functions, ExecBatchIterator is used to iterate over batches in smaller units. It is implemented by calling Array::slice(). For small batches, this is unecessary, since only one slice is created. The slice operation still causes some overhead by copying the shrared_ptrs of the ArrayData object, inclung the type pointer, which can lead to contention (ARROW-16161).

This Patch checks if the batch size is smaller than the slice size first, and uses std::move in this case.

I have attached a comparision of the ExecuteScalarExpressionOverhead benchmark here: avoid-slicing-performance.txt 

(created with --benchmark_min_time=20, the standard low runtime tends to be noisy with this, but also shows a positive tendency)

Issue Links

• relates to: ARROW-16755 [C++] Improve array expression and kernel evaluation performance on small inputs
• links to: GitHub Pull Request #13138