pg-logical-replication

pg-logical-replication

• PostgreSQL Logical Replication client for node.js
• Supported plugins
  • wal2json (Recommended)
  • pgoutput (Native to PostgreSQL)
  • decoderbufs
  • test_decoding (Not recommended)
• Document for old version(1.x)

1. Install

• pg-logical-replication depends on pq(node-postgres) >= 6.2.2 and eventemitter2

$ npm install pg-logical-replication

2. Usage

• This is an example using wal2json. A replication slot(test_slot_wal2json) must be created on the PostgreSQL server.
  • SELECT * FROM pg_create_logical_replication_slot('test_slot_wal2json', 'wal2json')

const slotName = 'test_slot_wal2json';

const service = new LogicalReplicationService(
  /**
   * node-postgres Client options for connection
   * https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/pg/index.d.ts#L16
   */
  {
    database: 'playground',
    // ...
  },
  /**
   * Logical replication service config
   * https://github.com/kibae/pg-logical-replication/blob/main/src/logical-replication-service.ts#L9
   */
  {
    acknowledge: {
      auto: true,
      timeoutSeconds: 10
    }
  }
)

// `TestDecodingPlugin` for test_decoding and `ProtocolBuffersDecodingPlugin` for decoderbufs are also available.
const plugin = new Wal2JsonDecodingPlugin({
  /**
   * Plugin options for wal2json
   * https://github.com/kibae/pg-logical-replication/blob/main/src/output-plugins/wal2json/wal2json-plugin-options.type.ts
   */
  //...
});

/**
 * Wal2Json.Output
 * https://github.com/kibae/pg-logical-replication/blob/ts-main/src/output-plugins/wal2json/wal2json-plugin-output.type.ts
 */
service.on('data', (lsn: string, log: Wal2Json.Output) => {
  // Do something what you want.
  // log.change.filter((change) => change.kind === 'insert').length;
});

// Start subscribing to data change events.
(function proc() {
  service.subscribe(plugin, slotName)
    .catch((e) => {
      console.error(e);
    })
    .then(() => {
      setTimeout(proc, 100);
    });
})();

---

3. LogicalReplicationService

3-1. Constructor(clientConfig: ClientConfig, config?: Partial<LogicalReplicationConfig>)

const service = new LogicalReplicationService(
  /**
   * node-postgres Client options for connection
   * https://github.com/DefinitelyTyped/DefinitelyTyped/blob/master/types/pg/index.d.ts#L16
   */
  clientConfig: {
    user?: string | undefined;
    database?: string | undefined;
    password?: string | (() => string | Promise<string>) | undefined;
    port?: number | undefined;
    host?: string | undefined;
    connectionString?: string | undefined;
    keepAlive?: boolean | undefined;
    stream?: stream.Duplex | undefined;
    statement_timeout?: false | number | undefined;
    parseInputDatesAsUTC?: boolean | undefined;
    ssl?: boolean | ConnectionOptions | undefined;
    query_timeout?: number | undefined;
    keepAliveInitialDelayMillis?: number | undefined;
    idle_in_transaction_session_timeout?: number | undefined;
    application_name?: string | undefined;
    connectionTimeoutMillis?: number | undefined;
    types?: CustomTypesConfig | undefined;
    options?: string | undefined;
  },
  /**
   * Logical replication service config
   * https://github.com/kibae/pg-logical-replication/blob/main/src/logical-replication-service.ts#L9
   */
  config?: Partial<{
    acknowledge?: {
      /**
       * If the value is false, acknowledge must be done manually.
       * Default: true
       */
      auto: boolean;
      /**
       * Acknowledge is performed every set time (sec). If 0, do not do it.
       * Default: 10
       */
      timeoutSeconds: 0 | 10 | number;
    };
  }>
)

3-2. subscribe(plugin: AbstractPlugin, slotName: string, uptoLsn?: string): Promise<this>

• Receive changes from the server.
• plugin output plugins.
• slotName Logical replication slot name. You can create slot via pg_create_logical_replication_slot function.
• uptoLsn (optional) The starting point of the data to be streamed.

3-3. acknowledge(lsn: string): Promise<boolean>

• After processing the data, it signals the PostgreSQL server that it is OK to clear the WAL log.
• Usually this is done automatically.
• Manually use only when new LogicalReplicationService({}, {acknowledge: {auto: false}}).

3-4. Event

• on(event: 'start', listener: () => Promise<void> | void)
  • Emitted when start replication.
• on(event: 'data', listener: (lsn: string, log: any) => Promise<void> | void)
  • Emitted when PostgreSQL data changes. The log value type varies depending on the plugin.
• on(event: 'error', listener: (err: Error) => void)
• on(event: 'acknowledge', listener: (lsn: string) => Promise<void> | void)
  • Emitted when acknowledging automatically.
• on(event: 'heartbeat', listener: (lsn: string, timestamp: number, shouldRespond: boolean) => Promise<void> | void)
  • A heartbeat check signal has been received from the server. You may need to run service.acknowledge().

3-5. Misc. method

• stop(): Promise<this>
  • Terminate the server's connection and stop replication.
• isStop(): boolean
  • Returns false when replication starts from the server.
• lastLsn(): string
  • Returns the last LSN(Log Sequence Number) received from the server.

---

4. Output Plugins

4-1. Wal2JsonDecodingPlugin for wal2json (Recommended)

4-2. ProtocolBuffersDecodingPlugin for decoderbufs

4-3. TestDecodingPlugin for test_decoding (Not recommended)

Contributors