Proposers

zhangminglei

Approvers

Status

Current state: 

Discussion thread: 

JIRA: 

Released: 

Current

SQL statements for DML are executed by Hive Driver with concatenation SQL statements in most cases. More importantly, multiple versions of Hive cannot be supported at the moment. The way SQL is concatenated is hard to maintain and the code is easy to break. Not supporting multiple versions of Hive creates a lot of headaches for users to use. 

for example, the following function use driver to execute sql.

HiveSyncTool#syncHoodieTable, for creating a database
HoodieHiveClient#createTable, for creating a table
HoodieHiveClient#addPartitionsToTable
HoodieHiveClient#updatePartitionsToTable
HoodieHiveClient#updateTableDefinition, alter table

Other than that, HoodieHiveClient#updateTableProperties, HoodieHiveClient#scanTablePartitions, HoodieHiveClient#doesTableExist and etc, those metadata operation use client api to execute sql.

The Improvement Proposal

We need to abstract a unified interface completely for all stuff contact with HMS and does not use Driver to execute DML. For supporting multiple version, we can add a shim middle layer to support multiple versions of HMS and allow user to specify the hive version in use.

Middle layer supports

we can use a wrapper to wrap a IMetaStoreClient and HiveShim , thus we can create different version of IMetaStoreClient by using HiveShim#getHiveMetastoreClient. The pseudocode below illustrates this process.

HiveShim hiveShim = HiveShimLoader.loadHiveShim(hiveVersion);

IMetaStoreClient createMetastoreClient() {
    return hiveShim.getHiveMetastoreClient(hiveConf);
}

IMetaStoreClient client = createMetastoreClient();

DML executor

We can also use the wrapper to wrap all dml operation or a fraction of them like create database, create table, add partition, update partition and etc. The pseudocode below shown the process.

	public void createDatabase(Database database)
			throws InvalidObjectException, AlreadyExistsException, MetaException, TException {
		client.createDatabase(database);
	}

	public void createTable(Table table)
			throws AlreadyExistsException, InvalidObjectException, MetaException, NoSuchObjectException, TException {
		client.createTable(table);
	}

 		public Partition add_partition(Partition partition)
			throws InvalidObjectException, AlreadyExistsException, MetaException, TException {
		return client.add_partition(partition);
	}

	public int add_partitions(List<Partition> partitionList)
			throws InvalidObjectException, AlreadyExistsException, MetaException, TException {
		return client.add_partitions(partitionList);
	}

HiveShimLoader

• Added interface HiveShim to define methods that need shimming.
• Implemented HiveShimV1 and HiveShimV2 for 1.x and 2.x respectively.
• Added HiveShimLoader to automatically load HiveShim.