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https://issues.apache.org/jira/browse/ARROW-4503?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17661525#comment-17661525
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Rok Mihevc commented on ARROW-4503:
-----------------------------------
This issue has been migrated to [issue
#21055|https://github.com/apache/arrow/issues/21055] on GitHub. Please see the
[migration documentation|https://github.com/apache/arrow/issues/14542] for
further details.
> [C#] ArrowStreamReader allocates and copies data excessively
> ------------------------------------------------------------
>
> Key: ARROW-4503
> URL: https://issues.apache.org/jira/browse/ARROW-4503
> Project: Apache Arrow
> Issue Type: Improvement
> Components: C#
> Reporter: Eric Erhardt
> Assignee: Eric Erhardt
> Priority: Major
> Labels: performance, pull-request-available
> Fix For: 0.14.0
>
> Original Estimate: 48h
> Time Spent: 12h 10m
> Remaining Estimate: 35h 50m
>
> When reading `RecordBatch` instances using the `ArrowStreamReader` class, it
> is currently allocating and copying memory 3 times for the data.
> # It is allocating memory in order to [read the data from the
> Stream|https://github.com/apache/arrow/blob/044b418fa108a57f0b4e2e887546cc3e68271397/csharp/src/Apache.Arrow/Ipc/ArrowStreamReader.cs#L72-L74],
> and then reading from the Stream. (This should be the only allocation that
> is necessary.)
> # It then [creates a new
> `ArrowBuffer.Builder`|https://github.com/apache/arrow/blob/044b418fa108a57f0b4e2e887546cc3e68271397/csharp/src/Apache.Arrow/Ipc/ArrowStreamReader.cs#L227-L228],
> which allocates another `byte[]`, and calls `Append` on it, which copies the
> values to the new `byte[]`.
> # Finally, it then calls `.Build()` on the `ArrowBuffer.Builder`, which
> [allocates memory from the MemoryPool, and then copies the intermediate
> buffer|https://github.com/apache/arrow/blob/044b418fa108a57f0b4e2e887546cc3e68271397/csharp/src/Apache.Arrow/ArrowBuffer.Builder.cs#L112-L121]
> into it.
>
> We should reduce this overhead to only allocating a single time (from the
> MemoryPool), and not copying the data more times than necessary.
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