Hi Team, Since the work begin to separate the HMS to a standalone project we thought that it would be useful the create extensive API tests for the public APIs of the new project. We started to create tests using the IMetaStoreClient interface implementations and found that not surprisingly the happy paths are working as expected, but there are some gaps in the exception handling. Most of the enhancements affect the Thrift API as well. We went through the following methods: Functions Indexes Tables Databases We also plan to comb through at least the Partition related methods too.
The possible enhancements we found could be grouped to the following categories: Bugs: For example IMetaStoreClient.drop/alter/createFunction with null function name might throw NullPointerException exception - this is clearly a bug which should be solved: Embedded MetaStore throws NullPointerException Remote MetaStore client throws TTransportException Sub-optimal error handling: For example IMetaStoreClient.alterFunction will not check if the new function is already exist, and tries to insert it anyway. After 10 tries it throws a MetaException where the exception text is "Update of object [...] failed : java.sql.SQLIntegrityConstraintViolationException [...]". Fixing this could be done without interface change, but following the logic of the other methods on the interface AlreadyExistsException should be thrown. Inconsistent exception handling: Different methods will throw different exceptions for similar errors. This makes the interface hard to understand, hard to document and maintain. For example: Calling IMetaStoreClient.createTable with nonexistent database name will throw InvalidObjectException Calling IMetaStoreClient.createFunction with nonexistent database name database will throw NoSuchObjectException There are some cases when the Embedded MetaStore handles error differently than the Remote MetaStore. For example: IMetaStoreClient.dropTable with "null" as a database: Embedded MetaStore throws MetaException Remote MetaStore client throws TProtocolException Proposed changes: Fixing cases 1. and 2. is a simple bug fix - it could be done independently Fixing cases 3. and 4. will change how the IMetaStoreClient and HMS Thrift API works. For these we should review the IMetaStoreClient and HMS Thrift API interface exception handling, to create consistent and easy to follow rules for the possible exceptions. We propose to keep the current exceptions, and only change when the given type of exceptions are thrown. If we stick to this then the interface will be binary backward compatible since currently every method defines TException as a throwable and every exception is inherited from TException. I think we allowed to change this since 3.0.0 is a major release. Do we agree with the general direction of these changes? Thanks, Peter
