Discussion thread	-
Vote thread	-
JIRA	-
Release	-

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

In our production, we create Flink Session Cluster and users can perform OLAP query in it. Users like to use Jdbc Driver in their applications to submit queries and get results. Currently we use the old flink-sql-gateway[1] and flink-jdbc-driver[2], but when we try to upgrade our Flink Session Cluster, We meet compatibility problem. Flink Sql Gateway has been a submodule in Flink, and the API has been greatly optimized. The old Flink JDBC Driver cannot connect to the new Gateway directly which cause we cannot upgrade our Flink version. In this FLIP, I'd like to introduce Flink Jdbc Driver module in Flink to connect Gateway, users can use Jdbc Driver to submit their queries and get results like a database in their applications.

Proposal

Architecture

Currently users can use Flink Sql Client to connect Sql Gateway as followed

SqlGateway starts Rest Service, and SqlClient can connect to it. Executor creates RestClient according to the address of Rest Service, then it can create Session, Submit Sql and Fetch Result according to RestClient.

We propose Flink Jdbc Driver interacts with SqlGateway through Executor too.

There are four main classes in Flink Jdbc Driver: FlinkDriver, FlinkConnection, FlinkStatement and FlinkResultSet which implement jdbc interface Driver, Connection, Statement and Result.

FlinkDriver parses gateway address from url, and creates FlinkConnection
FlinkConnection creates Executor according to gateway address. When the Connections is closed, it can close the connection with gateway by Executor
FlinkStatement can get Executor from FlinkConnection, and submit sql query to it. After query is executed, FlinkStatement can get StatementResult from Executor, and create FlinkResultSet
FlinkResultSet is an iterator, it gets results from StatementResult and return them to users

The call relationship between them are as followed.

User Case

Flink Jdbc Driver project will be packaged into an independent jar file such as flink-table-jdbc-driver-{version}.jar , which will contains classes of flink jdbc driver and shaded flink classes such as data type. User only need to add dependecy in pom.xml or add the jar in the classpath of external jdbc tools such as sqlite.

<dependency>
    <groupId>org.apache.flink</groupId>
    <artifactId>flink-table-jdbc-driver</artifactId>
    <version>${flink.version}</version>
</dependency>

More information about Flink Jdbc Driver

Driver Name: org.apache.flink.table.jdbc.FlinkDriver
Flink Connection URL: Users can use default catalog and database directly, or set them in url. They can set custom parameters in url to open the session in SqlGateway with key1=val1&key2=val2&...
1. jdbc:flink://{sql-gateway.host}:{sql-gateway.port}?key1=val1&key2=val2
2. jdbc:flink://{sql-gateway.host}:{sql-gateway.port}/{catalog name}?key1=val1&key2=val2
3. jdbc:flink://{sql-gateway.host}:{sql-gateway.port}/{catalog name}/{database name}?key1=val1&key2=val2

Use Flink Jdbc Driver in Java code

String driverName = "org.apache.flink.table.jdbc.FlinkDriver";
String url = "jdbc:flink://{sql-gateway.host}:{sql-gateway.port}/catalog/database?key1=val1&key2=val2";
Class.forName(driverName);

try (Connection connection = DriverManager.getConnection(url)) {
    try (Statement statement = connection.createStatement()) {
        try (ResultSet resultSet = statement.execute("SELECT * FROM {Your Table}")) {
            while (resultSet.hasNext()) {
                ....
            }
        }
    }
}

User can also add the flink-table-jdbc-driver-{version}.jar to the classpath of external jdbc tools.

Data Types

We support to convert the following flink data type to sql data type in this FLIP, and more types can be supported as needed in the future.

Flink Data Type	Jdbc Sql Data Type
CharType/VarCharType	String
BooleanType	Boolean
TinyIntType	Byte
SmallIntType	Short
IntType	Int
BigIntType	Long
FloatType	Float
DoubleType	Double
DecimalType	BigDecimal
BinaryType/VarBinaryType	(byte[]) Bytes
DateType	Date
TimeType	Time
TimestampType	Timestamp
ArrayType	Array

Public Interface

There are many functions in Jdbc Driver, while this FLIP only implement the basic functions first and more functions will be supported later. The mainly related interfaces are as follows.

Methods in FlinkDriver

/* Jdbc Driver for flink sql gateway */
public class FlinkDriver implements Driver {
    /* Connect sql gateway with given url and open/create session with given priperties. */
	@Override
    public Connection connect(String url, Properties info) throws SQLException;
}

Methods in FlinkConnection

/* Connection to flink sql gateway for jdbc driver. */
public class FlinkConnection implements Connection {
    /* Create statement from connection. */
	@Override
    public Statement createStatement() throws SQLException;
    
    /* Close session in sql gateway. */
 	@Override
    public void close() throws SQLException;
    
    /* Use given catalog to the session in sql gateway. */
 	@Override 
    public void setCatalog(String catalog) throws SQLException;
    
    /* Get current catalog name from session. */
 	@Override 
    public String getCatalog() throws SQLException;
    
    /* Get FlinkDatabaseMetaData instance for the current catalog. */
 	@Override 
    public DatabaseMetaData getMetaData() throws SQLException;
    
    /* Use given database to the session in sql gateway. */
 	@Override 
    public void setSchema(String schema) throws SQLException;
    
    /* Get current database name from session. */
 	@Override 
    public String getSchema() throws SQLException;
}

Methods in FlinkStatement

/* Statement in flink jdbc driver. */
public class FlinkStatement implements Statement {
    /* Submit sql to sql gateway and get result set. */
 	@Override  
    public ResultSet executeQuery(String sql) throws SQLException;
    
    /* Execute given update sql and return result count. */
 	@Override  
    public int executeUpdate(String sql) throws SQLException;
    
    /* Cancel the running job in sql gateway. */
 	@Override  
    public void close() throws SQLException;
    
    /* Return true if the result set has more results. */
 	@Override  
    public boolean getMoreResults() throws SQLException;
    
    /* Get current result set in the statement. */
 	@Override
    public ResultSet getResultSet() throws SQLException;
}

Methods in FlinkResultSet : FlinkResultSet only supports to fetching data from iterator StatementResult , it supports getXXX methods and doesn't support deleting, updating or moving the cursor.

/* ResultSet for flink jdbc driver. */
public class FlinkResultSet implements ResultSet {
    /* Return true if there are more resuts in result iterator. */
 	@Override 
    public boolean next() throws SQLException;
    
    /* Close the fetch result operation. */
 	@Override 
    public void close() throws SQLException;
    
    /* Get different values according to data type and column index. */
 	@Override 
    public <V> V getXXX(int columnIndex) throws SQLException.
    
    /* Get different values according to data type and column name. */
 	@Override
    public <V> V getXXX(String columnName) throws SQLException.
}

Methods in FlinkDatabaseMetaData : FlinkDatabaseMetaData only supports TABLE and VIEW tables, getting information of catalog, database and tables.

/* DatabaseMetaData in flink sql driver. */
public class FlinkDatabaseMetaData implements DatabaseMetaData {
    /* Get the url of flink sql driver. */
 	@Override 
    public String getURL() throws SQLException;
    
    /* Get catalog name list from session. */
 	@Override 
    public ResultSet getCatalogs() throws SQLException;
    
    /* Get database name list from session. */
 	@Override 
    public ResultSet getSchemas() throws SQLException;
    
    /* Get database name lins in given catalog from session. */
 	@Override 
    public ResultSet getSchemas(String catalog, String schemaPattern) throws SQLException;
    
    /* Get table name list with given condition from session. */
 	@Override 
    public ResultSet getTables(String catalog, String schemaPattern, String tableNamePattern, String[] types) throws SQLException;
    
    /* Get column list with given condition from session. */
 	@Override 
    public ResultSet getColumns(String catalog, String schemaPattern, String tableNamePattern, String columnNamePattern) throws SQLException;
    
    /* Get primary key list for given table from session. */
 	@Override 
    public ResultSet getPrimaryKeys(String catalog, String schema, String table) throws SQLException;
}

Methods in FlinkResultSetMetaData : FlinkResultSetMetaData only supports to getting column information according to column index or name.

/* ResultSetMetaData in flink sql driver. */
public class FlinkResultSetMetaData implements ResultSetMetaData {
    /* Get column count in the result set. */
 	@Override 
    public int getColumnCount() throws SQLException;
    
    /* If the column may be null. */
 	@Override 
    public int isNullable(int column) throws SQLException;
    
    /* Get display size for the column. */
 	@Override 
    public int getColumnDisplaySize(int column) throws SQLException;
    
    /* Get column name according to column index. */
 	@Override 
    public String getColumnLabel(int column) throws SQLException;
    public String getColumnName(int column) throws SQLException;
    
    /* Get precision for the column index. */
 	@Override 
    public int getPrecision(int column) throws SQLException;
    
    /* Get column type id for the column index. */
 	@Override 
    public int getColumnType(int column) throws SQLException;
    
    /* Get column type name for the column index. */
 	@Override 
    public String getColumnTypeName(int column) throws SQLException;
    
    /* Get column type class name for the column index. */
 	@Override 
    public String getColumnClassName(int column) throws SQLException;
}

Unsupported Ability

Don't support transaction such as commit, rollback
Don't support prepare statement, prepare call and etc operations
Don't support management operations such as savepoint and etc

[1] https://github.com/ververica/flink-sql-gateway

[2] https://github.com/ververica/flink-jdbc-driver

Page tree

FLIP-293: Introduce Flink Jdbc Driver For Sql Gateway