Print connector - Realtime Compute for Apache Flink - Alibaba Cloud Documentation Center

This topic describes how to use the Print connector.

Background information

The Print connector is used to write every row to the system output or system error stream. It is designed for debugging. To view the intermediate results or the output of a Flink deployment, you can add a print result table. Then, you can view the result data in TaskManager logs as prompted.

The Print connector can be used to check whether the messages sent to other result tables meet the expectations.

The following table describes the capabilities supported by the Print connector.

Item	Description
Table type	Result table and data ingestion sink
Running mode	Batch mode and streaming mode
Data format	N/A
Metric	N/A
API type	SQL API and data ingestion YAML API
Data update or deletion in a sink table	Supported

Prerequisites

If you want to view the output of a Print result table, make sure that the log level is set to INFO.
A maximum of 2,000 log entries can be displayed in Taskmanager.out. If you want to check for dirty data or specific data, we recommend that you specify conditions in the WHERE clause to perform the print operation. The print operation allows you to effectively check required data, even when the number of data records displayed is limited.

SQL

Syntax

CREATE TABLE print_table (
  a INT,
  b varchar
) WITH (
  'connector'='print',
  'logger'='true'
);

You can also create a Print table by using the LIKE clause based on an existing table schema. Sample statement:

CREATE TABLE print_table WITH ('connector' = 'print')
LIKE table_source (EXCLUDING ALL)

Parameters in the WITH clause

Parameter	Description	Data type	Required	Default value	Remarks
connector	The type of the table.	String	Yes	No default value	Set the value to print.
logger	Specifies whether to display the data result in the console.	Boolean	No	false	Valid values: false: The data result is not displayed in the console. This is the default value. true: The data result is displayed in the console.
print-identifier	The identifier of the data result.	String	No	No default value	The log information is retrieved by using the identifier of the data result.
sink.parallelism	The parallelism of the result table.	Int	No	A value that is the same as the upstream parallelism	N/A.

Data ingestion

YAML drafts for data ingestion can use the values connector to print data to out files or logs.

Syntax

source:
  type: xxx

sink:
  type: values
  name: Values Sink
  print.enabled: true

Parameters in the WITH clause

Parameter	Description	Data type	Required	Default value	Remarks
type	The connector type of a sink	STRING	Yes	No default value	The value is fixed to values.
name	The connector name of a sink	STRING	No	No default value	N/A.
print.enabled	Whether the connector is used as the Print connector	BOOLEAN	Yes	No default value	The value is fixed to true.
materialized.in.memory	Whether to persist binary log events to the memory.	BOOLEAN	No	false	N/A.
sink.print.standard-error	Whether to print the format to system error instead of system out.	BOOLEAN	No	false	By default, the format is printed to the system out.
sink.print.logger	Whether to display the result data on the console.	BOOLEAN	No	false	N/A.
sink.print.limit	The maximum number of data records to print.	LONG	No	2000	N/A.
error.on.schema.change	Whether an error is reported when a schema change occurs.	BOOLEAN	No	false	N/A.

Sample code

Sample code for a result table

CREATE TEMPORARY TABLE table_source(
  name VARCHAR,
  score BIGINT
) WITH (
  ...
);

CREATE TEMPORARY TABLE print_sink(
  name VARCHAR,
  score BIGINT
) WITH (
  'connector' = 'print'
);

INSERT INTO print_sink SELECT * from table_source;

Data ingestion sink

source:
  type: mysql
  name: MySQL Source
  hostname: ${mysql.hostname}
  port: ${mysql.port}
  username: ${mysql.username}
  password: ${mysql.password}
  tables: ${mysql.source.table}
  server-id: 7601-7604

sink:
  type: values
  name: Values Sink
  print.enabled: true