see also in the following parquet issue:
Currently, if we change parquet format hive table using "alter table parquet_table change c1 c1 bigint " ( assuming original type of c1 is int), it will result in exception thrown from SerDe: "org.apache.hadoop.io.IntWritable cannot be cast to org.apache.hadoop.io.LongWritable" in query runtime.
This is different behavior from hive (using other file format), where it will try to perform cast (null value in case of incompatible type).
Parquet Hive's RecordReader returns an ArrayWritable (based on schema stored in footers of parquet files); ParquetHiveSerDe also creates an corresponding ArrayWritableObjectInspector (but using column type info from metastore). Whenever there is column type change, the objector inspector will throw exception, since WritableLongObjectInspector cannot inspect an IntWritable etc...
Conversion has to happen somewhere if we want to allow type change. SerDe's deserialize method seems a natural place for it.
Currently, serialize method calls createStruct (then createPrimitive) for every record, but it creates a new object regardless, which seems expensive. I think that could be optimized a bit by just returning the object passed if already of the right type. deserialize also reuse this method, if there is a type change, there will be new object to be created, which I think is inevitable.