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PG Stream

Store kafka-node events into a postgres database.

Using

yarn add @ovotech/kafka-pg-sink

Each topic from the consumer stream gets its own "resolver" function that converts the message to an array of values, directly inserted as columns in the database.

INSERT INTO tableName VALUES (column1Value, column2Value ...) ON CONFLICT DO NOTHING
import { PGSinkStream, Message } from '@ovotech/kafka-pg-sink';
import { ConsumerGroupStream } from 'kafka-node';
import { Client } from 'pg';

const consumerStream = new ConsumerGroupStream(
  { kafkaHost: 'localhost:29092', groupId: 'my-group', encoding: 'buffer' },
  ['migration-completed'],
);

const pg = new Client('postgresql://postgres:[email protected]:5432/postgres');
const pgSink = new PGSinkStream({
  pg,
  topics: {
    'migration-completed': {
      table: 'migration_completed',
      resolver: (message: Message) => {
        const data = getDataSomehow(message.value);
        return [data.column1, data.column2, data];
      },
    },
  },
});

consumerStream.pipe(pgSink);

Message is the same as the type from kafka-node, but is more lenient on the "value field". This allows you to pre-process the message before sending it off to pg-sink, by deserializing an using avro for example.

export interface Message {
  topic: string;
  value: any;
  offset?: number;
  partition?: number;
  highWaterOffset?: number;
  key?: string;
}

Usage with a deserializer

You can transform kafka events with a transform stream before they arrive to the sink. For example with @ovotech/avro-stream.

import { AvroDeserializer, AvroMessage } from '@ovotech/avro-stream';
import { PGSinkStream } from '@ovotech/kafka-pg-sink';
import { ConsumerGroupStream } from 'kafka-node';

const consumerStream = new ConsumerGroupStream(
  { kafkaHost: 'localhost:29092', groupId: 'my-group', encoding: 'buffer' },
  ['migration-completed'],
);
const deserializer = new AvroDeserializer('http://localhost:8080');
const pg = new Client('postgresql://postgres:[email protected]:5432/postgres');
const pgSink = new PGSinkStream({
  pg,
  topics: {
    'migration-completed': {
      table: 'migration_completed',
      resolver: (message: AvroMessage) => [message.value.accountId],
    },
  },
});

consumerStream.pipe(deserializer).pipe(pgSink);

Errors

PGSinkStream can emit an PGSinkError and PGSinkMultipleError depending on whether it was processing batched or normal requests.

PGSinkError

Property Description
message Original error message
chunk The event sent from the previous stream to be saved to the database (Message)
encoding The buffer encoding
originalError The original error object that was triggered

PGSinkMultipleError

Property Description
message Original error message
chunks An array of { chunk: Message, encoding: string } objects
originalError The original error object that was triggered

Example error handling:

import { PGSinkStream, PGSinkError, PGSinkMultipleError } from '@ovotech/kafka-pg-sink';

const pgSink = new PGSinkStream();

pgSink.on('error', (error: PGSinkError | PGSinkMultipleError) => {
  if (error instanceof PGSinkError) {
    console.log(error.chunk);
  }
});

Gotchas

A thing to be aware of is that node streams unpipe in an event of an error, which means that you'll need to provide your own error handling and repipe the streams if you want it to be resilient to errors.

Running the tests

The tests require a running postgres database. This is setup easily with a docker-compose from root project folder:

docker-compose up

Then you can run the tests with:

yarn test

Coding style (linting, etc) tests

Style is maintained with prettier and tslint

yarn lint

Deployment

Deployment is preferment by lerna automatically on merge / push to master, but you'll need to bump the package version numbers yourself. Only updated packages with newer versions will be pushed to the npm registry.

Contributing

Have a bug? File an issue with a simple example that reproduces this so we can take a look & confirm.

Want to make a change? Submit a PR, explain why it's useful, and make sure you've updated the docs (this file) and the tests (see test folder).

License

This project is licensed under Apache 2 - see the LICENSE file for details