stiga-huang opened a new pull request #1008:
URL: https://github.com/apache/orc/pull/1008
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### What changes were proposed in this pull request?
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This PR fixes an unhandled case when seeking in an uncompressed chunk.
### Why are the changes needed?
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The bug causes position overflow and fails the reader when encountered the
unhandled case. Some background:
* Compressed streams are compressed in chunks. If the compressed size of a
chunk is larger than the original size, the original (uncompressed) chunk will
be kept. The chunk header records the chunk length and whether it's compressed.
* Seek position in a compressed stream is encoded into 2 numbers: pos in the
input stream and pos in the chunk. The first number locates the chunk header.
The second number locates the position in the decompressed chunk.
* Compressed chunks are decompressed in a whole so the whole chunk is in the
output buffer. Uncompressed chunks don't need decompression so the input buffer
is used directly. However, the chunk could be read in pieces depending on the
block size of the input stream. So the seek position might not be loaded yet.
The unhandled case is: the seek position is in the current chunk but
posInChunk is not loaded yet. We should skip the remaining bytes to seek to it.
### How was this patch tested?
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Added a unit test in TestDecompression.cc. Verified the issue described in
the JIRA is resolved.
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