kasakrisz opened a new pull request, #6491:
URL: https://github.com/apache/hive/pull/6491
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### What changes were proposed in this pull request?
* Use custom DTOs to store column statistics and ensure that
serialVersionUID is specified explicitly.
* Modify `StatsUtils.estimateStatsForMissingCols` to return a new list of
column statistics instead of adding the newly estimated stats to its input
parameter.
### Why are the changes needed?
* Currently, Thrift-generated objects are serialized when storing the column
statistics of an Iceberg table. However, the `serialVersionUID` is not
explicitly specified, hence the Java compiler generates one at build time. This
can lead to compatibility issues when a newer Hive version attempts to read
column stats from a table created by an older version.
* When reading the column statistics of an Iceberg table fails,
`Collections.emptyList()` is returned. Because this is an unmodifiable list,
the current implementation of `estimateStatsForMissingCols` [tries to
add](https://github.com/apache/hive/blob/1516fb91e8a622b4655b0e07a37fb449634c1637/ql/src/java/org/apache/hadoop/hive/ql/stats/StatsUtils.java#L254-L257)
the estimated column statistics to it and an exception is thrown.
### Does this PR introduce _any_ user-facing change?
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No.
### How was this patch tested?
```
mvn test -Dtest=TestHiveIcebergStatistics -pl iceberg/iceberg-handler
mvn test -Dtest.output.overwrite -DskipSparkTests
-Dtest=TestIcebergLlapLocalCliDriver -Dqfile=merge_iceberg_partitioned_orc.q
-pl itests/qtest-iceberg -Pitests
```
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