manolama opened a new pull request, #38423:
URL: https://github.com/apache/arrow/pull/38423
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### Rationale for this change
Java is missing delta encoding for dictionaries per
https://arrow.apache.org/docs/status.html. This PR will implement delta
encoding and a helper to easily write dictionary encoded columns in batched
streams and files.
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### What changes are included in this PR?
Adds a new `BaseDictionary` interface that the original `Dictionary`
implements. A new `BatchedDictionary` is added that allows for writing data to
the dictionary in batches that are then flushed to an IPC stream or file. On
flush, the `BatchedDictionary` is reset to support delta encoding or
replacement (for streams only).
Also adds a flag to the `DictionaryEncoding` to enable delta encoding.
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### Are these changes tested?
Yes, multiple unit tests on IPC files and streams. Not tested with add-on
libraries.
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### Are there any user-facing changes?
Yes with new APIs. Existing APIs are backwards compatible so no code changes
are needed.
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