Hive 3 classes present in hive-iceberg-runtime.jar breaks running on Hive 2

[massdosage]

If you try deploy the version of iceberg-hive-runtime in master on Hive 2 one gets exceptions like this:

2020-10-19T11:19:25,011 ERROR [8aadf788-a388-4641-88f6-4e7a07e8929e main([])]: exec.DDLTask (DDLTask.java:failed(639)) - java.lang.NoClassDefFoundError: org/apache/hadoop/hive/serde2/io/DateWritableV2
        at java.lang.Class.getDeclaredMethods0(Native Method)
        at java.lang.Class.privateGetDeclaredMethods(Class.java:2729)
        at java.lang.Class.privateGetMethodRecursive(Class.java:3076)
        at java.lang.Class.getMethod0(Class.java:3046)
        at java.lang.Class.getMethod(Class.java:1812)
        at org.apache.iceberg.common.DynMethods$Builder.impl(DynMethods.java:305)
        at org.apache.iceberg.common.DynMethods$Builder.impl(DynMethods.java:264)
        at org.apache.iceberg.common.DynMethods$Builder.impl(DynMethods.java:283)
        at org.apache.iceberg.mr.hive.serde.objectinspector.IcebergObjectInspector.<clinit>(IcebergObjectInspector.java:40)
        at org.apache.iceberg.mr.hive.HiveIcebergSerDe.initialize(HiveIcebergSerDe.java:67)

This is because the Hive3 object inspector classes are present in the runtime jar:

jar -tf 9d98b1d.dirty/iceberg-hive-runtime-9d98b1d.dirty.jar  | grep Hive3
org/apache/iceberg/mr/hive/serde/objectinspector/IcebergDateObjectInspectorHive3.class
org/apache/iceberg/mr/hive/serde/objectinspector/IcebergTimestampObjectInspectorHive3$1.class
org/apache/iceberg/mr/hive/serde/objectinspector/IcebergTimestampObjectInspectorHive3$2.class
org/apache/iceberg/mr/hive/serde/objectinspector/IcebergTimestampObjectInspectorHive3.class

which means it attempts to load these object inspectors which in turn fails as the required Hive 3 classes aren't on the classpath.

I'm pretty sure this issue started happening after the changes introduced in #1478.

[massdosage]

@marton-bod could you look at the above? I haven't had time to try come up with a solution but my first guess would be that we're going to need a hive2-runtime jar and a hive3-runtime jar.

[marton-bod]

Thanks @massdosage. I think we can avoid having to create a different runtime jar for Hive2, we'll just have to use MetastoreUtil.hive3PresentOnClasspath() to select the correct object inspector at runtime. I'll post a fix as soon as I can.

[massdosage]

OK, yes, sounds like a good option.