tustvold opened a new pull request, #3558:
URL: https://github.com/apache/arrow-rs/pull/3558
# Which issue does this PR close?
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Closes #506
Relates to #2832
# Rationale for this change
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MutableArrayData blindly concatenates the dictionary values arrays together
when given multiple different dictionaries. This is straightforward and often
fast, but degrades spectacularly if either of the following hold:
* The dictionary values are large
* Not all dictionary values are referenced by the keys (e.g. the array has
been filtered / sliced, read from parquet)
This leads to high memory usage, wasted CPU cycles, and potential byte array
offset overflow
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# Are there any user-facing changes?
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