wypoon opened a new pull request #26895: [SPARK-17398][SQL] Fix ClassCastException when querying partitioned JSON table URL: https://github.com/apache/spark/pull/26895 ### What changes were proposed in this pull request? When querying a partitioned table with format `org.apache.hive.hcatalog.data.JsonSerDe` and more than one task runs in each executor concurrently, the following exception is encountered: `java.lang.ClassCastException: java.util.ArrayList cannot be cast to org.apache.hive.hcatalog.data.HCatRecord` The exception occurs in `HadoopTableReader.fillObject`. `org.apache.hive.hcatalog.data.JsonSerDe#initialize` populates a `cachedObjectInspector` field by calling `HCatRecordObjectInspectorFactory.getHCatRecordObjectInspector`, which is not thread-safe; this `cachedObjectInspector` is returned by `JsonSerDe#getObjectInspector`. We protect against this Hive bug by synchronizing on an object when we need to call `initialize` on `org.apache.hadoop.hive.serde2.Deserializer` instances (which may be `JsonSerDe` instances). By doing so, the `ObjectInspector` for the `Deserializer` of the partitions of the JSON table and that of the table `SerDe` are the same cached `ObjectInspector` and `HadoopTableReader.fillObject` then works correctly. (If the `ObjectInspector`s are different, then a bug in `HCatRecordObjectInspector` causes an `ArrayList` to be created instead of an `HCatRecord`, resulting in the `ClassCastException` that is seen.) ### Why are the changes needed? To avoid a bug in Hive. ### Does this PR introduce any user-facing change? No. ### How was this patch tested? Tested manually on a cluster with a partitioned JSON table and running a query using more than one core per executor. Before this change, the ClassCastException happens consistently. With this change it does not happen.
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