pg-trx-outbox

Transactional outbox of Postgres for Node.js with little Event Sourcing More info about Transactional Outbox pattern: https://microservices.io/patterns/data/transactional-outbox.html More info about Event Sourcing pattern: https://microservices.io/patterns/data/event-sourcing.html

DB structure

CREATE TABLE IF NOT EXISTS pg_trx_outbox (
  id bigserial NOT NULL,
  processed bool NOT NULL DEFAULT false,
  created_at timestamptz NOT NULL DEFAULT now(),
  updated_at timestamptz NOT NULL DEFAULT now(),
  since_at timestamptz,
  topic text NOT NULL,
  "key" text NULL,
  value jsonb NULL,
  "partition" int2 NULL,
  "timestamp" int8 NULL,
  headers jsonb NULL,
  response jsonb NULL,
  error text NULL,
  meta jsonb NULL,
  context_id double precision NOT NULL DEFAULT random(),
  attempts smallint NOT NULL DEFAULT 0,
  is_event bool NOT NULL DEFAULT false,
  CONSTRAINT pg_trx_outbox_pk PRIMARY KEY (id)
);

CREATE INDEX pg_trx_outbox_not_processed_idx
  ON pg_trx_outbox (processed, id)
  WHERE (processed = false);

Types of DB entities

Command

• Command it's row when is_event = false
• Command handled by one consumer only once (at least once in theory), Postgres SQL for update used for row locking
• Usually used for third-party integration
• May propagate events or another commands in same transaction

Event

• Event it's row when is_event = true
• Same event wlll be handled by all consumers
• Usually used for DB denormalization, cache creation, response providing, etc

Modes

Short polling mode

Messages polled from PostgreSQL using FOR UPDATE with COMMIT order. This batch of messaged produced to destination. Then messages marked as processed. This mode used by default.

Short polling example

Code

import { PgTrxOutbox } from 'pg-trx-outbox'

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnAdapter(), // about adapters see below
  outboxOptions: {
    mode: 'short-polling',
    pollInterval: 5000, // how often to poll PostgreSQL for new messages, default 5000 milliseconds
    limit: 50, // how much messages in batch, default 50
    onError(err) {/**/} // callback for catching uncaught error
  },
  eventSourcingOptions: {/* [2] */}
});

await pgTrxOutbox.start();

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L85

Notify mode

For reducing latency PostgreSQL LISTEN/NOTIFY can be used. When message inserted in DB, NOTIFY called and all listeners try to fetch new messages. Short polling mode also used here, because LISTEN/NOTIFY not robust mechanism and notifications can be lost.

Notify example

Deps

npm install --save pg-listen

SQL migration

CREATE OR REPLACE FUNCTION pg_trx_outbox() RETURNS trigger AS $trigger$
  BEGIN
    PERFORM pg_notify('pg_trx_outbox', '{}');
    RETURN NEW;
  END;
$trigger$ LANGUAGE plpgsql;

CREATE TRIGGER pg_trx_outbox AFTER INSERT ON pg_trx_outbox
EXECUTE PROCEDURE pg_trx_outbox();

Code

import { PgTrxOutbox } from 'pg-trx-outbox'

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnAdapter(), // about adapters see below
  outboxOptions: {
    mode: 'notify',
    pollInterval: 5000, // how often to poll PostgreSQL for new messages, default 5000 milliseconds
    limit: 50, // how much messages in batch, default 50
    onError(err) {/**/} // callback for catching uncaught error
  },
  eventSourcingOptions: {/* [2] */}
});

await pgTrxOutbox.start();

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L85

Create custom adapter for destination

Some adapters for Transactional Outbox destination are built-in. You can find it here: https://github.com/darky/pg-trx-outbox/tree/master/src/adapters But sometimes you want to create your own

Custom adapter example

import { PgTrxOutbox } from 'pg-trx-outbox'
import { Adapter } from 'pg-trx-outbox/dist/src/types'

class MyOwnAdapter implements Adapter {
  async start() {
    // some init logic here, establish connection and so on
  },
  
  async stop() {
    // some graceful shutdown logic here, close connection and so on
  },
  
  async send(messages) {
    // messages handling here
    // need return Promise.allSettled compatible array for each message in appropriate order
    
    return [
      // example of successful message handling
      { value: {someResponse: true}, status: 'fulfilled' },
      // example of exception while message handling
      { reason: 'some error text', status: 'rejected' },
      // Optional meta property can be returned
      // which will be saved in appropriate DB column
      { value: {someResponse: true}, status: 'fulfilled', meta: {someMeta: true} }
    ]
  },

  async onHandled(messages) {
    // some optional logic here for handled messages in batch
  }
}

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnAdapter(),
  outboxOptions: {
    /* [2] */
  }
});

await pgTrxOutbox.start();

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42

Built-in adapters for message handling order

SerialAdapter example

SerialAdapter can be used for handling messages of batch serially, step by step

import { PgTrxOutbox } from 'pg-trx-outbox'
import { SerialAdapter } from 'pg-trx-outbox/dist/src/adapters/abstract/serial'

class MyOwnAdapter extends SerialAdapter {
  async start() {
    // some init logic here, establish connection and so on
  },
  
  async stop() {
    // some graceful shutdown logic here, close connection and so on
  },
  
  async handleMessage(message) {
    // serial messages handling here, step by step
    
    // example of successful message handling
    return { value: {someResponse: true}, status: 'fulfilled' },
    // example of exception while message handling
    return { reason: 'some error text', status: 'rejected' },
    // Optional meta property can be returned
    // which will be saved in appropriate DB column
    return { value: {someResponse: true}, status: 'fulfilled', meta: {someMeta: true} }
  },

  async onHandled(messages) {
    // some optional logic here for handled messages in batch
  }
}

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnAdapter(),
  outboxOptions: {
    /* [2] */
  }
});

await pgTrxOutbox.start();

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42

ParallelAdapter example

ParallelAdapter can be used for handling messages in parallel independently of each other

import { PgTrxOutbox } from 'pg-trx-outbox'
import { ParallelAdapter } from 'pg-trx-outbox/dist/src/adapters/abstract/parallel'

class MyOwnAdapter extends ParallelAdapter {
  async start() {
    // some init logic here, establish connection and so on
  },
  
  async stop() {
    // some graceful shutdown logic here, close connection and so on
  },
  
  async handleMessage(message) {
    // parallel messages handling here
    
    // example of successful message handling
    return { value: {someResponse: true}, status: 'fulfilled' },
    // example of exception while message handling
    return { reason: 'some error text', status: 'rejected' },
    // Optional meta property can be returned
    // which will be saved in appropriate DB column
    return { value: {someResponse: true}, status: 'fulfilled', meta: {someMeta: true} }
  },

  async onHandled(messages) {
    // some optional logic here for handled messages in batch
  }
}

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnAdapter(),
  outboxOptions: {
    /* [2] */
  }
});

await pgTrxOutbox.start();

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42

GroupedAdapter example

GroupedAdapter is combination of SerialAdapter and ParallelAdapter Messages with same key will be handled serially, step by step. But messages with different key will be handled in parallel

import { PgTrxOutbox } from 'pg-trx-outbox'
import { GroupedAdapter } from 'pg-trx-outbox/dist/src/adapters/abstract/grouped'

class MyOwnAdapter extends GroupedAdapter {
  async start() {
    // some init logic here, establish connection and so on
  },
  
  async stop() {
    // some graceful shutdown logic here, close connection and so on
  },
  
  async handleMessage(message) {
    // grouped by `key` message handling here
    
    // example of successful message handling
    return { value: {someResponse: true}, status: 'fulfilled' },
    // example of exception while message handling
    return { reason: 'some error text', status: 'rejected' },
    // Optional meta property can be returned
    // which will be saved in appropriate DB column
    return { value: {someResponse: true}, status: 'fulfilled', meta: {someMeta: true} }
  },

  async onHandled(messages) {
    // some optional logic here for handled messages in batch
  }
}

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnAdapter(),
  outboxOptions: {
    /* [2] */
  }
});

await pgTrxOutbox.start();

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42

Partitioning

Over time, performance of one table pg_trx_outbox can be not enough. Also, handling messages throughput can be not enough too. In this cases native PostgreSQL partitioning can help and pg-trx-outbox supports it. Implementation inspired by Kafka key partitioning mechanism.

Partitioning example

SQL migration

CREATE TABLE pg_trx_outbox (
  id bigserial NOT NULL,
  processed bool NOT NULL DEFAULT false,
  created_at timestamptz NOT NULL DEFAULT now(),
  updated_at timestamptz NOT NULL DEFAULT now(),
  since_at timestamptz,
  topic text NOT NULL,
  "key" text NULL,
  value jsonb NULL,
  "partition" int2 NULL,
  "timestamp" int8 NULL,
  headers jsonb NULL,
  response jsonb NULL,
  error text NULL,
  meta jsonb NULL,
  context_id double precision NOT NULL DEFAULT random(),
  attempts smallint NOT NULL DEFAULT 0,
  CONSTRAINT pg_trx_outbox_pk PRIMARY KEY (id, key)
) PARTITION BY HASH (key);

CREATE TABLE pg_trx_outbox_0 PARTITION OF pg_trx_outbox FOR VALUES WITH (MODULUS 3, REMAINDER 0);
CREATE TABLE pg_trx_outbox_1 PARTITION OF pg_trx_outbox FOR VALUES WITH (MODULUS 3, REMAINDER 1);
CREATE TABLE pg_trx_outbox_2 PARTITION OF pg_trx_outbox FOR VALUES WITH (MODULUS 3, REMAINDER 2);

Code

import { PgTrxOutbox } from 'pg-trx-outbox'

const pgTrxOutbox0 = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnOrBuiltInAdapter(),
  outboxOptions: {
    partition: 0 // this istance of `PgTrxOutbox` will handle only `0` partition
    /* [2] */
  }
});
const pgTrxOutbox1 = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnOrBuiltInAdapter(),
  outboxOptions: {
    partition: 1 // this instance of `PgTrxOutbox` will handle only `1` partition
    /* [2] */
  }
});

await pgTrxOutbox0.start();
await pgTrxOutbox1.start();

const [{ id } = { id: '' }] = await pg
  .query<{ id: string }>(
    `
      INSERT INTO pg_trx_outbox (topic, "key", value)
      VALUES ('some.topic', 'someKey', '{"someValue": true}')
      RETURNING id;
    `
  )
  .then(resp => resp.rows)

try {
  // waitResponse can handle response from any partition
  // key passing will prune unnecessary partitions
  const waitResp = await pgTrxOutbox0.waitResponse<{someValue: boolean}>(id, 'someKey')
} catch(e) {
  // if error will be happens on message handling
}

// on shutdown

await pgTrxOutbox0.stop();
await pgTrxOutbox1.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42

Built-in messages meta

In Custom adapter section you already see, that meta field can be returned in message handling and implicitly will be saved in DB in appropriate column. Also pg-trx-outbox provide some built-in meta, which will be persisted with using of SerialAdapter, ParallelAdapter or GroupedAdapter:

{
  pgTrxOutbox: {
    time: 1.343434, // time of message handling execution, high-precision count of milliseconds
    libuv: { /* [1] */ }, // contains libuv metrics for detecting CPU stucks
    beforeMemory: { /* [2] */ }, // memory usage before event
    afterMemory: { /* [2] */ }, // memory usage after event
    uptime: 100, // [3] uptime of process
    cpuUsage: { /* [4] */ } // CPU usage per event
  }
}

• [1] https://nodejs.org/dist/latest-v20.x/docs/api/perf_hooks.html#class-histogram
• [2] https://nodejs.org/dist/latest-v20.x/docs/api/process.html#processmemoryusage
• [3] https://nodejs.org/dist/latest-v20.x/docs/api/process.html#processuptime
• [4] https://nodejs.org/dist/latest-v20.x/docs/api/process.html#processcpuusagepreviousvalue

Context id

Very useful to link chain of messages handling with through contextId More info about pattern: https://microservices.io/patterns/observability/distributed-tracing.html Using SerialAdapter, ParallelAdapter or GroupedAdapter very easy to extract contextId of current handled message and pass it futher:

import { PgTrxOutbox } from 'pg-trx-outbox'
import { SerialAdapter } from 'pg-trx-outbox/dist/src/adapters/abstract/serial'

class MyOwnAdapter extends SerialAdapter {
  async start() {
    // some init logic here, establish connection and so on
  },
  
  async stop() {
    // some graceful shutdown logic here, close connection and so on
  },
  
  async handleMessage(message) {
    // `contextId` can be extracted in any place of async stack and passed to futher
    // AsyncLocalStorage will used for this purpose [3]
    // `pg` is hypothetical object of your code, which means PostgreSQL client
    await pg.query(`
      insert into pg_trx_outbox (topic, "key", value, context_id)
      values ('some.topic', 'key', '{"someValue": true}', $1)
    `, [pgTrxOutbox.contextId()])
  },

  async onHandled(messages) {
    // some optional logic here for handled messages in batch
  }
}

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnAdapter(),
  outboxOptions: {
    /* [2] */
  }
});

await pgTrxOutbox.start();

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42
• [3] https://nodejs.org/dist/latest-v20.x/docs/api/async_context.html#class-asynclocalstorage

Filter messages handling by topic

Messages handling can be filtered by topic. It's useful, when you have multiple microservices with one shared DB and each microservice should handle specific bunch of messages filtered by topic.

More optimized index for not processed messages

CREATE INDEX pg_trx_outbox_not_processed_idx
  ON pg_trx_outbox (processed, topic, id)
  WHERE (processed = false);

Topics filter example

import { PgTrxOutbox } from 'pg-trx-outbox'

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnOrBuiltInAdapter(),
  outboxOptions: {
    topicFilter: ['for.handle'] // Array of topics, which should be handled only
    /* [2] */
  }
});

await pgTrxOutbox.start();

await pg
  .query<{ id: string }>(
    `
      INSERT INTO pg_trx_outbox (topic, "key", value)
      VALUES ('for.handle', 'someKey', '{"someValue": true}'), -- this message will be handled
        ('not.for.handle', 'someKey', '{"someValue": true}') -- this message not will be handled
    `
  )

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42

Scheduling of messages

Messages can be delayed and handled at some time in future

Messages scheduling example

import { PgTrxOutbox } from 'pg-trx-outbox'

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnOrBuiltInAdapter(),
  outboxOptions: {
    /* [2] */
  }
});

await pgTrxOutbox.start();

await pg
  .query<{ id: string }>(
    `
      INSERT INTO pg_trx_outbox (topic, "key", value, since_at)
      VALUES ('for.handle', 'someKey', '{"someValue": true}', now() + interval '1 hour'), -- this message will be handled since 1 hour
        ('not.for.handle', 'someKey', '{"someValue": true}', null), -- this message not will be handled ASAP
        ('not.for.handle', 'someKey', '{"someValue": true}', now() - interval '1 hour'), -- this message not will be handled ASAP
    `
  )

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42

Retrying of errors

Messages can be retried via predicate

Retrying of errors example

import { PgTrxOutbox } from 'pg-trx-outbox'

const pgTrxOutbox = new PgTrxOutbox({
  pgOptions: {/* [1] */},
  adapter: new MyOwnOrBuiltInAdapter(),
  outboxOptions: {
    retryError(err) {
      // return true for retrying
    },
    retryDelay: 5, // delay of retry in seconds, default is 5
    retryMaxAttempts: 5 // max attempts for retry, default is 5
    /* [2] */
  }
});

await pgTrxOutbox.start();

await pg
  .query<{ id: string }>(
    `
      INSERT INTO pg_trx_outbox (topic, "key", value)
      VALUES ('for.handle', 'someKey', '{"someValue": true}')
    `
  )

// on shutdown

await pgTrxOutbox.stop();

• [1] https://node-postgres.com/apis/pool
• [2] https://github.com/darky/pg-trx-outbox/blob/master/src/types.ts#L42