In the BATCH world, Hive is still the standard. Considering that Flink has continuously improved its compatibility with Hive in recent years, we propose to expose HiveServer2 Endpoint on the Flink SQL Gateway. The Endpoint will implement the thrift interface exposed by HiveServer2, and users' BI, CLI and other tools based on the HiveServer2 can also be seamlessly migrated to the Flink SQL Gateway.

HiveServer2 has 3 kinds of functionality:

• manage the metadata info in the Hive MetaStore
• translate the HiveSQL to the Operation and execute:
  • translate DML/QUERY to MapReduce job and submit the job to the Hadoop

• • translate to the Operation that manipulates the Hive MetaStore
• Users can lookup the Operation status and manage the submitted Operation.

Proposed Change

HiveServer2 has the similar architecture we describe in the FLIP-91. User should register the Session in the SessionManager before submitting the statement. After that, the user uses the SessionHandle to find the registered resources in the Session and execute the statements. All statements will be translated to the Operation and use the OperationHandle to fetch the results or logs. Therefore, the HiveServer2 endpoint gurantees:

1. The SessionHandle and OperationHandle in the HiveServer2 is able to convert to the SessionHandle and OperationHandle in the FLIP-91;
2. The interfaces exposed by the HiveServer2 can be converted into related calls in Flink GatewayService;

Handle

The structure of the Handle in the HiveServer2 is as follows.

The transfomration is as follows.

• HiveServer2 SessionHandle has the same structure with the Gateway SessionHandle
• The HiveServer2 OperationHandle has more information than the OperationHandle in the Gateway. HiveServer2 endpoint should use the result of the GatewayService#getOperationInfo to build the OperationHandle in the HiveServer2.

HiveServer2 Endpoint API

Refer to the file for the HiveServer2 API.

GatewayService API Change

public interface GatewayService {
    
    /**
     * Fetch the Operation-level log from the GatewayService.
     */
    ResultSet fetchLog(
        SessionHandle sessionHandle, 
        OperationHandle operationHandle, 
        FetchOrientation orientation, 
        int maxRows);
    
   /**
    * Only supports FORWARD/BACKWARD. 
    * - Users can only BACKWARD from the current offset once.
    * - The Gateway don't not materialize the changelog.
    */
    ResultSet fetchResult(
        SessionHandle sessionHandle, 
        OperationHandle operationHandle, 
        FetchOrientation orientation, 
        int maxRows
    );
}

enum FetchOrientation {
    FORWARD,
    BACKWARD
}

Session API

• OpenSession

• Usage：register a Session in the SessionManager
• Return：SessionHandle
• HiveServer2 Endpoint needs to do：

• Determine the communication version between HiveServer2 and Client;
• Invoke GatewayService#openSession to register the Session;
• Configure the Hive Environment

• Create the Hive Catalog
• Switch to the Hive Dialect
• Load the Hive Module

• CloseSession

• Usage: Clear the related resources;
• HiveServer2 Endpoint needs to do:

• Invoke the GatewayService#closeSession

Operation API

• GetOperationStatus

• Usage: Get the Operation status.
• HiveServer2 Endpoint needs to do:

• Invoke the GatewayService#getOperationStatus

• CancelOperation

• Usage: Cancel the Operation.
• HiveServer2 Endpoint needs to do:

• Invokes the GatewayService#cancelOperation

• CloseOperatio

• Usage: Close the Operation
• HiveServer2 Endpoint needs to do:

• Invoke the GatewayService#closeOperation

Statement API

• ExecuteStatement

• Usage: Execute the SQL to the Gateway Service synchronously or asynchronously.
• Return：OperationHandle
• HiveServer2 Endpoint needs to do：

• Invokes the GatewayService#executeStatement
• HiveServer2 supports to execute statement in the synchronous mode.

• ExecuteStatement with table.dml-sync is true.
• Currently the GatewayService only supports submission in asynchronous mode. It requires the HiveServer2 Endpoint to monitor Operation status.

• FetchResults

• Usage: Supports fetching the results or logs with fetch orientation to the client.
• HiveServer2 Endpoint needs to do：

• Invoke the GatewayService#fetchResults or GatewayService#fetchLog

• GetResultSetMetadata

• Usage: return the result schema
• HiveServer2 Endpoint needs to do：

• Invokes the GatewayService#getResultSchema。

• GetInfo

• Get cluster info。

• Only support to get the CLI_SERVER_NAME（FLINK) now. Extend other values if needed in the future.

• GetTypeInfo
  • Get the ODBC's  type info.

• GetCatalogs

• Return the registered Catalogs.

• • Do as follows:

/**
 * The schema for the Operation is 
 * <pre>
 * +-------------------------------+--------------+
 * | column name    | column type  | comments     |
 * +-------------------------------+--------------+
 * | TABLE_CAT      | STRING       | catalog name |
 * +-------------------------------+--------------+
 * </pre>
 */
gateway.submitOperation(
    HiveServer2OperationType.GET_CATALOGS,
    () -> convertToGetCatalogs(gateway.listCatalogs()), 
    resultSchema);

• GetSchemas

• Return the databases info。Currently HiveServer2 supports to use regex to filter out the unmatched database.
• Do as follow：

/**
 * The schema for the Operation is 
 * <pre>
 * +-------------------------------+--------------+
 * | column name    | column type  | comments     |
 * +-------------------------------+--------------+
 * | TABLE_SCHEMA   | STRING       | schema name  |
 * +-------------------------------+--------------+
 * | TABLE_CAT      | STRING       | catalog name |
 * +-------------------------------+--------------+
 * </pre>
 */
gateway.submitOperation(
    HiveServer2OperationType.GET_SCHEMAS,
    () -> {
         List<String> databases = filter(gateway.listDatabases(sessionHandle), databasePattern);
         return convertToGetDatabasesResultSet(databases);
    }, 
    resultSchema);

• GetTables

• Get the tables in the specified Catalog and Database. HiveServer2 allows to use the Catalog/Database/Table Pattern to filter out the unmatched tables.
• Do as follow：

/**
 * The schema for the Operation is 
 * <pre>
 * +-------------------------------+--------------------------------+
 * | column name    | column type  | comments                       |
 * +-------------------------------+--------------------------------+
 * | TABLE_CAT      | STRING       | catalog name                   |
 * +-------------------------------+--------------------------------+
 * | TABLE_SCHEMA   | STRING       | schema name                    |
 * +-------------------------------+--------------------------------+
 * | TABLE_NAME     | STRING       | table name                     |
 * +-------------------------------+--------------------------------+
 * | TABLE_TYPE     | STRING       | table type, e.g. TABLE, VIEW   |
 * +-------------------------------+--------------------------------+
 * | REMARKS        | STRING       | table desc                     |
 * +-------------------------------+--------------------------------+
 * </pre>
 */
gateway.submitOperation(
    HiveServer2OperationType.GET_TABLES,
    () -> {
        List<CatalogTable> results = new ArrayList<>(); 
        List<String> catalogs = filter(gateway.listCatalogs(sessionHandle), catalogPattern);
         for (String catalog: catalogs) {
             List<String> databases = filter(gateway.listDatabases(sessionHandle, catalog), databasePattern);
             for (String database: databases) {
                 List<String> tables = filter(gateway.listTables(sessionHandle, catalog, database), tablePattern);
                 for (String table: tables) {
                     results.add(gateway.getTable(catalog, database, table, ALL));
                 }
             }
         }
         return convertToGetTablesResultSet(results);
    }, 
    resultSchema);

• GetTableTypes

• Return the table types in the current catalog and current database.
• Do as follow.

/**
 * The schema for the Operation is 
 * <pre>
 * +-------------------------------+--------------------------------+
 * | column name    | column type  | comments                       |
 * +-------------------------------+--------------------------------+
 * | TABLE_TYPE     | STRING       | table type, e.g. TABLE, VIEW   |
 * +-------------------------------+--------------------------------+
 * | REMARKS        | STRING       | table desc                     |
 * +-------------------------------+--------------------------------+
 * </pre>
 */
gateway.submitOperaton(
    HiveServer2OperationType.GET_TABLE_TYPES,
    () -> {
        String catalog = gateway.getCurrentCatalog();
        String database = gateway.getCurrentDatbase();
        
        List<TableDescriptor> tables = gateway.listTables(catalog, database, ALL);
        return convertToGetTablesResultSet(results);
    }
)

• GetColumns

• Return the column info for the specified tables
• Should be similar to the GatTables

• GetPrimaryKeys

• Return the PK infos
• Should be similar to the GatTables

• GetFunctions

• Return the registered function infos
• Should be similar to the GatTables

Unsupported API

• GetCrossReference

Flink doesn't have the concepts about cross reference.

• GetDelegationToken、CancelDelegationToken、RenewDelegationToken

Flink doesn't support to get the delegation token from the Yarn side now. 

Configure HiveServer2 Endpoint

Options

We use the same style as the HiveServer2 options。

Example

endpoint.protocol: hiveserver2
endpoint.hiveserver2.port: 9002
endpoint.hiveserver2.catalog.hive-conf-dir: /path/to/catalog

Implementation

HiveServer2 uses the Apache Thrift framework. The server is composed of 3 parts.

• Transport determines how the client communicates with the server。Now HiveServer2 supports http and binary mode.
• Protocol is responsible for serialization and deserialization。Currently HiveServer2 uses the TBinaryProtocol.
• Processor is the application logic to handle requests 。We should rewrite the Processor with the Flink logic.

Therefore, we relies on the hive-service-rpc which contains HiveServer2 API and thrift dependencies. We will use the Hive-2.3.x as the Endpoint version, which is the most popular. Considering the HiveServer2 endpoint is lightweight and needs to work with the Hive Catalog, we just merge the HiveServer2 Endpoint into the flink-connector-hive module.