sadikovi opened a new pull request, #38277:
URL: https://github.com/apache/spark/pull/38277
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### What changes were proposed in this pull request?
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This PR is a follow-up for
https://github.com/databricks/runtime/commit/3bc6fe4e77e1791c0a20387240e93d0175e0fade.
In the original commit, `spark.hadoopRDD.ignoreEmptySplits` was enabled due to
seemingly no side-effects, however, this change breaks `SymlinkTextInputFormat`
any table that uses the input format would return empty results.
This is due to a combination of problems:
1. Incorrect implementation of
[SymlinkTextInputSplit](https://github.com/apache/hive/blob/master/ql/src/java/org/apache/hadoop/hive/ql/io/SymlinkTextInputFormat.java#L73).
The input format does not set `start` and `length` fields from the target
split. `SymlinkTextInputSplit` is an abstraction over FileSplit and all
downstream systems treat it as such - those fields should be extracted and
passed from the target split.
2. `spark.hadoopRDD.ignoreEmptySplits` being enabled causes HadoopRDD to
filter out all of the empty splits which does not work in the case of
SymlinkTextInputFormat. This is due to 1. Because we don't set any length (and
start) those splits are considered to be empty and are removed from the final
list of partitions even though the target splits themselves are non-empty.
Technically, this needs to be addressed in Hive but I figured it would be
much faster to fix this in Spark.
### Why are the changes needed?
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Fixes a correctness issue when using `SymlinkTextInputSplit` in Spark.
### Does this PR introduce _any_ user-facing change?
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No.
### How was this patch tested?
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I added a unit test that reproduces the issue and verified that it passes
with the fix.
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