autumnust opened a new pull request #909:
URL: https://github.com/apache/orc/pull/909
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### What changes were proposed in this pull request?
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There's individual instance of `OutStream` within each TreeWriter created by
`WriterContext#createStream` method. Within `OutStream`, there are totally 3
buffers:
- current: the regular input buffer holding uncompressed, unencrypted bytes.
- compress: the output buffer holding compressed bytes
- overflow: same as "compress" but only used when the last compression
output is larger than remaining capacity of compress buffer.
Potentially the compress and overflow buffer don't have to be allocated
individually within each `OutStream` object, but shared across all of them so
to save memory allocation.
This PR is the first step for sharing the compression output buffer, which
refactors internal of `OutStream` and make the relevant object bundled together
since they are logically related(and details of dealing with overflow doesn't
have to be visible). This refactoring makes it easier to share the compression
output buffer as a pass-in arguments in the follow-up PR.
### Why are the changes needed?
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For the context of ORC-997, this change makes the compression output buffer,
as a single entity, easier to be shared and passed in from caller.
### How was this patch tested?
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There's no functional changes from this PR so passing all existed unit
tests. Also added a new test in `TestOutStream` to make sure that, the scenario
where `codec.compress()` returns false (meaning the compression output is
larger than original input) is also covered in the unit test.
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