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聊聊flink的JDBCAppendTableSink

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本文主要研究一下flink的JDBCAppendTableSink

实例

JDBCAppendTableSink sink = JDBCAppendTableSink.builder()
  .setDrivername("org.apache.derby.jdbc.EmbeddedDriver")
  .setDBUrl("jdbc:derby:memory:ebookshop")
  .setQuery("INSERT INTO books (id) VALUES (?)")
  .setParameterTypes(INT_TYPE_INFO)
  .build();

tableEnv.registerTableSink(
  "jdbcOutputTable",
  // specify table schema
  new String[]{"id"},
  new TypeInformation[]{Types.INT},
  sink);

Table table = ...
table.insertInto("jdbcOutputTable");

这里使用tableEnv.registerTableSink注册JDBCAppendTableSink，之后利用table.insertInto往该sink写数据

JDBCAppendTableSink

flink-jdbc_2.11-1.7.0-sources.jar!/org/apache/flink/api/java/io/jdbc/JDBCAppendTableSink.java

public class JDBCAppendTableSink implements AppendStreamTableSink<Row>, BatchTableSink<Row> {

    private final JDBCOutputFormat outputFormat;

    private String[] fieldNames;
    private TypeInformation[] fieldTypes;

    JDBCAppendTableSink(JDBCOutputFormat outputFormat) {
        this.outputFormat = outputFormat;
    }

    public static JDBCAppendTableSinkBuilder builder() {
        return new JDBCAppendTableSinkBuilder();
    }

    @Override
    public void emitDataStream(DataStream<Row> dataStream) {
        dataStream
                .addSink(new JDBCSinkFunction(outputFormat))
                .name(TableConnectorUtil.generateRuntimeName(this.getClass(), fieldNames));
    }

    @Override
    public void emitDataSet(DataSet<Row> dataSet) {
        dataSet.output(outputFormat);
    }

    @Override
    public TypeInformation<Row> getOutputType() {
        return new RowTypeInfo(fieldTypes, fieldNames);
    }

    @Override
    public String[] getFieldNames() {
        return fieldNames;
    }

    @Override
    public TypeInformation<?>[] getFieldTypes() {
        return fieldTypes;
    }

    @Override
    public TableSink<Row> configure(String[] fieldNames, TypeInformation<?>[] fieldTypes) {
        int[] types = outputFormat.getTypesArray();

        String sinkSchema =
            String.join(", ", IntStream.of(types).mapToObj(JDBCTypeUtil::getTypeName).collect(Collectors.toList()));
        String tableSchema =
            String.join(", ", Stream.of(fieldTypes).map(JDBCTypeUtil::getTypeName).collect(Collectors.toList()));
        String msg = String.format("Schema of output table is incompatible with JDBCAppendTableSink schema. " +
            "Table schema: [%s], sink schema: [%s]", tableSchema, sinkSchema);

        Preconditions.checkArgument(fieldTypes.length == types.length, msg);
        for (int i = 0; i < types.length; ++i) {
            Preconditions.checkArgument(
                JDBCTypeUtil.typeInformationToSqlType(fieldTypes[i]) == types[i],
                msg);
        }

        JDBCAppendTableSink copy;
        try {
            copy = new JDBCAppendTableSink(InstantiationUtil.clone(outputFormat));
        } catch (IOException | ClassNotFoundException e) {
            throw new RuntimeException(e);
        }

        copy.fieldNames = fieldNames;
        copy.fieldTypes = fieldTypes;
        return copy;
    }

    @VisibleForTesting
    JDBCOutputFormat getOutputFormat() {
        return outputFormat;
    }
}

JDBCAppendTableSink实现了AppendStreamTableSink接口的emitDataStream方法以及BatchTableSink接口的emitDataSet方法；AppendStreamTableSink接口及BatchTableSink接口都继承自TableSink接口，该接口定义了getOutputType、getFieldNames、getFieldTypes、configure方法
emitDataStream方法通过JDBCOutputFormat创建JDBCSinkFunction，然后输出到dataStream；emitDataSet方法则直接通过dataSet的output方法采用JDBCOutputFormat输出
JDBCAppendTableSink提供了builder静态方法用于创建JDBCAppendTableSinkBuilder，可以用来构建JDBCAppendTableSink

JDBCAppendTableSinkBuilder

flink-jdbc_2.11-1.7.0-sources.jar!/org/apache/flink/api/java/io/jdbc/JDBCAppendTableSinkBuilder.java

public class JDBCAppendTableSinkBuilder {
    private String username;
    private String password;
    private String driverName;
    private String dbURL;
    private String query;
    private int batchSize = DEFAULT_BATCH_INTERVAL;
    private int[] parameterTypes;

    /**
     * Specify the username of the JDBC connection.
     * @param username the username of the JDBC connection.
     */
    public JDBCAppendTableSinkBuilder setUsername(String username) {
        this.username = username;
        return this;
    }

    /**
     * Specify the password of the JDBC connection.
     * @param password the password of the JDBC connection.
     */
    public JDBCAppendTableSinkBuilder setPassword(String password) {
        this.password = password;
        return this;
    }

    /**
     * Specify the name of the JDBC driver that will be used.
     * @param drivername the name of the JDBC driver.
     */
    public JDBCAppendTableSinkBuilder setDrivername(String drivername) {
        this.driverName = drivername;
        return this;
    }

    /**
     * Specify the URL of the JDBC database.
     * @param dbURL the URL of the database, whose format is specified by the
     *              corresponding JDBC driver.
     */
    public JDBCAppendTableSinkBuilder setDBUrl(String dbURL) {
        this.dbURL = dbURL;
        return this;
    }

    /**
     * Specify the query that the sink will execute. Usually user can specify
     * INSERT, REPLACE or UPDATE to push the data to the database.
     * @param query The query to be executed by the sink.
     * @see org.apache.flink.api.java.io.jdbc.JDBCOutputFormat.JDBCOutputFormatBuilder#setQuery(String)
     */
    public JDBCAppendTableSinkBuilder setQuery(String query) {
        this.query = query;
        return this;
    }

    /**
     * Specify the size of the batch. By default the sink will batch the query
     * to improve the performance
     * @param batchSize the size of batch
     */
    public JDBCAppendTableSinkBuilder setBatchSize(int batchSize) {
        this.batchSize = batchSize;
        return this;
    }

    /**
     * Specify the type of the rows that the sink will be accepting.
     * @param types the type of each field
     */
    public JDBCAppendTableSinkBuilder setParameterTypes(TypeInformation<?>... types) {
        int[] ty = new int[types.length];
        for (int i = 0; i < types.length; ++i) {
            ty[i] = JDBCTypeUtil.typeInformationToSqlType(types[i]);
        }
        this.parameterTypes = ty;
        return this;
    }

    /**
     * Specify the type of the rows that the sink will be accepting.
     * @param types the type of each field defined by {@see java.sql.Types}.
     */
    public JDBCAppendTableSinkBuilder setParameterTypes(int... types) {
        this.parameterTypes = types;
        return this;
    }

    /**
     * Finalizes the configuration and checks validity.
     *
     * @return Configured JDBCOutputFormat
     */
    public JDBCAppendTableSink build() {
        Preconditions.checkNotNull(parameterTypes,
            "Types of the query parameters are not specified." +
            " Please specify types using the setParameterTypes() method.");

        JDBCOutputFormat format = JDBCOutputFormat.buildJDBCOutputFormat()
            .setUsername(username)
            .setPassword(password)
            .setDBUrl(dbURL)
            .setQuery(query)
            .setDrivername(driverName)
            .setBatchInterval(batchSize)
            .setSqlTypes(parameterTypes)
            .finish();

        return new JDBCAppendTableSink(format);
    }
}

JDBCAppendTableSinkBuilder提供了setUsername、setPassword、setDrivername、setDBUrl、setQuery、setBatchSize、setParameterTypes方法用于设置构建JDBCOutputFormat的对应属性，最后build方法使用JDBCOutputFormat创建了JDBCAppendTableSink

小结

JDBCAppendTableSink在开启checkpoint的情况下，它实现的是at-least-once的语义，如果要实现exactly-once的语义，则需要使用类似REPLACE或者INSERT OVERWRITE这类幂等的操作；JDBCAppendTableSink实现了AppendStreamTableSink接口的emitDataStream方法以及BatchTableSink接口的emitDataSet方法
AppendStreamTableSink接口及BatchTableSink接口都继承自TableSink接口，该接口定义了getOutputType、getFieldNames、getFieldTypes、configure方法；emitDataStream方法通过JDBCOutputFormat创建JDBCSinkFunction，然后输出到dataStream；emitDataSet方法则直接通过dataSet的output方法采用JDBCOutputFormat输出；JDBCAppendTableSink提供了builder静态方法用于创建JDBCAppendTableSinkBuilder，可以用来构建JDBCAppendTableSink
JDBCAppendTableSinkBuilder提供了setUsername、setPassword、setDrivername、setDBUrl、setQuery、setBatchSize、setParameterTypes方法用于设置构建JDBCOutputFormat的对应属性，最后build方法使用JDBCOutputFormat创建了JDBCAppendTableSink