Valery Meleshkin created ARROW-4650:
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Summary: The patch for PARQUET-1508 leads to infinite loop and
infinite memory allocation when reading very sparse ByteArray columns
Key: ARROW-4650
URL: https://issues.apache.org/jira/browse/ARROW-4650
Project: Apache Arrow
Issue Type: Bug
Components: C++
Reporter: Valery Meleshkin
In this loop
[https://github.com/apache/arrow/commit/3d435e4f8d5fb7a54a4a9d285e1a42d60186d8dc#diff-47fe879cb9baad6c633c55f0a34a09c3R739]
The branch of if dealing with null values does not increment variable 'i'.
Therefore on chunks containing only NULLs once a thread enters the loop, it
stays in that loop forever. I'm not entirely sure whether 'num_values' variable
was meant to be the number of non-NULL values, yet the total number of values
is passed here
[https://github.com/apache/arrow/blob/3d435e4f8d5fb7a54a4a9d285e1a42d60186d8dc/cpp/src/parquet/arrow/record_reader.cc#L528]
On my local machine adding `++i` to the NULL-handling branch seems to fix the
problem. Unfortunately, I'm not familiar with the codebase enough to be certain
it's a proper fix.
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