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https://issues.apache.org/jira/browse/ARROW-11030?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17256141#comment-17256141
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Jorge Leitão commented on ARROW-11030:
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[~andygrove], the MutableArrayData is basically:
# bound to a bunch of existing Arrays (of the same type), so that it can "copy
slices of slots" from any of those arrays
# It uses the arrays' DataType to extend the buffers and child_data according
to the spec
The parameter "capacity" (in number of slots) is used to reserve all buffers
that we can reserve upfront (e.g. primitive types and offsets). In the case of
a concat, we can compute that parameter exactly, since it is the sum of all
arrays lens:
https://github.com/apache/arrow/blob/f4ccceb2536bb6ed5bf584843c55c6628ad23494/rust/arrow/src/compute/kernels/concat.rs#L57
The `new` function allocates closures (one per array without child data) that
are optimized to extend buffers accordingly.
> [Rust] [DataFusion] MutableArrayData slow with many batches
> -----------------------------------------------------------
>
> Key: ARROW-11030
> URL: https://issues.apache.org/jira/browse/ARROW-11030
> Project: Apache Arrow
> Issue Type: Bug
> Components: Rust - DataFusion
> Reporter: Andy Grove
> Assignee: Andy Grove
> Priority: Major
> Fix For: 3.0.0
>
>
> Performance of joins slows down dramatically with smaller batches.
> The issue is related to slow performance of MutableDataArray::new() when
> passed a high number of batches. This happens when passing in all of the
> batches from the build side of the join and this happens once per build-side
> join key for each probe-side batch.
> It seems to get exponentially slower as the number of arrays increases even
> though the number of rows is the same.
> I modified hash_join.rs to have this debug code:
> {code:java}
> let start = Instant::now();
> let row_count: usize = arrays.iter().map(|arr| arr.len()).sum();
> let num_arrays = arrays.len();
> let mut mutable = MutableArrayData::new(arrays, true, capacity);
> if num_arrays > 0 {
> debug!("MutableArrayData::new() with {} arrays containing {} rows took {}
> ms", num_arrays, row_count, start.elapsed().as_millis());
> } {code}
> Batch size 131072:
> {code:java}
> MutableArrayData::new() with 4584 arrays containing 3115341 rows took 1 ms
> MutableArrayData::new() with 4584 arrays containing 3115341 rows took 1 ms
> MutableArrayData::new() with 4584 arrays containing 3115341 rows took 1 ms
> {code}
> Batch size 16384:
> {code:java}
> MutableArrayData::new() with 36624 arrays containing 3115341 rows took 19 ms
> MutableArrayData::new() with 36624 arrays containing 3115341 rows took 16 ms
> MutableArrayData::new() with 36624 arrays containing 3115341 rows took 17 ms
> {code}
> Batch size 4096:
> {code:java}
> MutableArrayData::new() with 146496 arrays containing 3115341 rows took 88 ms
> MutableArrayData::new() with 146496 arrays containing 3115341 rows took 89 ms
> MutableArrayData::new() with 146496 arrays containing 3115341 rows took 88 ms
> {code}
>
>
>
>
>
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