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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. The RFC is divided into two steps to finish, (mainly at the code level). The first part is to support multiple versions of Hive( first priority ) and the second part refactor the DML executor. We do not encourage users to manually configure the Hive version, but we still do provide a configuration for users to set it if they specify it.
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, other functions to be shimmed will also be represented in this interface .The pseudocode below illustrates this process.
public interface HiveShim extends Serializable { /** * Create a Hive Metastore client based on the given HiveConf object. * * @param hiveConf HiveConf instance * @return an IMetaStoreClient instance */ IMetaStoreClient getHiveMetastoreClient(HiveConf hiveConf); /** * Alters a Hive table. * * @param client the Hive metastore client * @param databaseName the name of the database to which the table belongs * @param tableName the name of the table to be altered * @param table the new Hive table */ void alterTable(IMetaStoreClient client, String databaseName, String tableName, Table table) throws InvalidOperationException, MetaException, TException; void alterPartition(IMetaStoreClient client, String databaseName, String tableName, Partition partition) throws InvalidOperationException, MetaException, TException; ... ... ... } 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
we add a shim loader to load HiveShim.
- Added interface
HiveShim
to define methods that need shimming. - Implemented
HiveShimV1
andHiveShimV2
for 1.x and 2.x respectively. - Added
HiveShimLoader
to automatically load HiveShim.
hudi on flink refactor
StreamWriteOperatorCoordinator#syncHive needs to rewrite in order to fit the new framework.