PostgreSQL-CDC

Overview

The PostgreSQL Extract Node allows for reading snapshot data and incremental data from PostgreSQL database. This document describes how to set up the PostgreSQL Extract Node to run SQL queries against PostgreSQL databases.

Supported Version

Extract Node	Version	Driver
PostgreSQL-CDC	PostgreSQL: 9.6, 10, 11, 12	JDBC Driver: 42.2.12

Dependencies

In order to set up the PostgreSQL Extract Node, the following provides dependency information for both projects using a build automation tool (such as Maven or SBT) and SQL Client with Sort Connectors JAR bundles.

Maven dependency

<dependency>
    <groupId>org.apache.inlong</groupId>
    <artifactId>sort-connector-postgres-cdc</artifactId>
    <version>1.6.0</version>
</dependency>

Setup PostgreSQL server

Change Data Capture (CDC) allows you to track and propagate changes in a PostgreSQL database to downstream consumers based on its Write-Ahead Log (WAL). You need to ensure that the upstream database is configured to support logical replication. Before using the PostgreSQL connector to monitor the changes committed on a PostgreSQL server, decide which logical decoding plug-in you intend to use. If you plan not to use the native pgoutput logical replication stream support, then you must install the logical decoding plug-in into the PostgreSQL server.

pgoutput

pgoutput is the standard logical decoding output plug-in in PostgreSQL 10+. It is maintained by the PostgreSQL community, and used by PostgreSQL itself for logical replication. This plug-in is always present so no additional libraries need to be installed.

1. Check the wal_level configuration setting:

SHOW wal_level;

The default value is replica. For CDC, you’ll need to set it to logical in the database configuration file (postgresql.conf). Keep in mind that changing the wal_level requires a restart of the Postgres instance and can affect database performance.

2. To configure the replication slot regardless of the decoder being used, specify the following in the postgresql.conf file:

wal_level = logical 

decoderbufs

decoderbufs is based on Protobuf and maintained by the Debezium community. installing it.

1. To load the plug-in at startup, add the following to the postgresql.conf file:

shared_preload_libraries = 'decoderbufs'

2. To configure the replication slot regardless of the decoder being used, specify the following in the postgresql.conf file:

wal_level = logical 

replica identity

REPLICA IDENTITY is a PostgreSQL-specific table-level setting that determines the amount of information that is available to the logical decoding plug-in for UPDATE and DELETE events. See more.

Please keep the replica indentity level of source tables to FULL. You can check and change this value by SQL:

-- show replica identity
SELECT CASE relreplident
  WHEN 'd' THEN 'default'
  WHEN 'n' THEN 'nothing'
  WHEN 'f' THEN 'full'
  WHEN 'i' THEN 'index'
  END AS replica_identity
FROM pg_class
WHERE oid = 'mytablename'::regclass;

-- change replica identity
ALTER TABLE mytablename REPLICA IDENTITY FULL;

How to create a PostgreSQL Extract Node

Usage for SQL API

CREATE TABLE `postgresTable`(
  `name` STRING,
  `age` INT
) WITH (
  'connector' = 'postgres-cdc-inlong',
  'hostname' = 'localhost',
  'username' = 'postgres',
  'password' = 'inlong',
  'database-name' = 'postgres',
  'schema-name' = 'public',
  'port' = '5432',
  'table-name' = 'user',
  'decoding.plugin.name' = 'pgoutput',
  'slot.name' = 'feaafacbaddadc'
)

Usage for InLong Dashboard

TODO: It will be supported in the future.

Usage for InLong Manager Client

TODO: It will be supported in the future.

PostgreSQL Extract Node Options

Option	Required	Default	Type	Description
connector	required	(none)	String	Specify what connector to use, here should be postgres-cdc-inlong.
hostname	required	(none)	String	IP address or hostname of the PostgreSQL database server.
username	required	(none)	String	Name of the PostgreSQL database to use when connecting to the PostgreSQL database server.
password	required	(none)	String	Password to use when connecting to the PostgreSQL database server.
database-name	required	(none)	String	Database name of the PostgreSQL server to monitor.
schema-name	required	(none)	String	Schema name of the PostgreSQL database to monitor.
table-name	required	(none)	String	Table name of the PostgreSQL database to monitor.
port	optional	5432	Integer	Integer port number of the PostgreSQL database server.
decoding.plugin.name	optional	decoderbufs	String	The name of the Postgres logical decoding plug-in installed on the server. Supported values are decoderbufs, wal2json, wal2json_rds, wal2json_streaming, wal2json_rds_streaming and pgoutput.
slot.name	optional	flink	String	The name of the PostgreSQL logical decoding slot that was created for streaming changes from a particular plug-in for a particular database/schema. The server uses this slot to stream events to the connector that you are configuring. Slot names must conform to PostgreSQL replication slot naming rules, which state: "Each replication slot has a name, which can contain lower-case letters, numbers, and the underscore character."
debezium.*	optional	(none)	String	Pass-through Debezium's properties to Debezium Embedded Engine which is used to capture data changes from Postgres server. For example: 'debezium.snapshot.mode' = 'never'. See more about the Debezium's Postgres Connector properties.
inlong.metric.labels	optional	(none)	String	Inlong metric label, format of value is groupId={groupId}&streamId={streamId}&nodeId={nodeId}.

caution

• slot.name is recommended to set for different tables to avoid the potential PSQLException: ERROR: replication slot "flink" is active for PID 974 error.
• PSQLException: ERROR: all replication slots are in use Hint: Free one or increase max_replication_slots. We can delete slot by the following statement.

SELECT * FROM pg_replication_slots;

-- get slot name is flink. delete it
SELECT pg_drop_replication_slot('flink');

Available Metadata

The following format metadata can be exposed as read-only (VIRTUAL) columns in a table definition.

key	Data Type	Description
table_name	STRING NOT NULL	Name of the table that contain the row.
schema_name	STRING NOT NULL	Name of the schema that contain the row.
database_name	STRING NOT NULL	Name of the database that contain the row.
op_ts	TIMESTAMP_LTZ(3) NOT NULL	It indicates the time that the change was made in the database. If the record is read from snapshot of the table instead of the change stream, the value is always 0.

The extended CREATE TABLE example demonstrates the syntax for exposing these metadata fields:

CREATE TABLE postgresTable (
    db_name STRING METADATA FROM 'database_name' VIRTUAL,
    table_name STRING METADATA  FROM 'table_name' VIRTUAL,
    operation_ts TIMESTAMP_LTZ(3) METADATA FROM 'op_ts' VIRTUAL,
    `name` STRING,
    `age` INT
) WITH (
     'connector' = 'postgres-cdc-inlong',
     'hostname' = 'localhost',
     'username' = 'postgres',
     'password' = 'inlong',
     'database-name' = 'postgres',
     'schema-name' = 'public',
     'port' = '5432',
     'table-name' = 'user',
     'decoding.plugin.name' = 'pgoutput',
     'slot.name' = 'feaafacbaddadc'
);

Data Type Mapping

PostgreSQL type	Flink SQL type
	TINYINT
SMALLINT INT2 SMALLSERIAL SERIAL2	SMALLINT
INTEGER SERIAL	INT
BIGINT BIGSERIAL	BIGINT
	DECIMAL(20, 0)
REAL FLOAT4	FLOAT
FLOAT8 DOUBLE PRECISION	DOUBLE
NUMERIC(p, s) DECIMAL(p, s)	DECIMAL(p, s)
BOOLEAN	BOOLEAN
DATE	DATE
TIME [(p)][WITHOUT TIMEZONE]	TIME [(p)][WITHOUT TIMEZONE]
TIMESTAMP [(p)]WITHOUT TIMEZONE	TIMESTAMP [(p)][WITHOUT TIMEZONE]
CHAR(n) CHARACTER(n) VARCHAR(n) CHARACTER VARYING(n) TEXT	STRING
BYTEA	BYTES