sharedb-milestone-mongo

MongoDB milestone snapshot database adapter for sharedb. Milestone snapshots can be used to speed up the results of ShareDB's connection.fetchSnapshot method by providing points in time on top of which a smaller number of ops can be applied to reach the requested version.

Milestone snapshots will be stored in a collection called m_COLLECTION where COLLECTION is the name of your ShareDB collection.

Quick start

const MongoMilestoneDB = require('sharedb-milestone-mongo');
const ShareDB = require('sharedb');

const milestoneDb = new MongoMilestoneDB('mongodb://localhost:27017/test');
const shareDb = new ShareDB({ milestoneDb: milestoneDb });

Configuration

Mongo

The underlying Mongo database can be configured in a number of ways. This library wraps v2 of the mongodb library, so any configuration that can be used there can be used in this library.

Mongo can be configured simply using a connection string and any desired options:

const milestoneDb = new MongoMilestoneDB('mongodb://localhost:27017/test', { loggerLevel: 'debug' });

It can also be configured with a callback that provides an instance of a Mongo Db object:

const mongodb = require('mongodb');

const milestoneDb = new MongoMilestoneDB((callback) => {
  mongodb.connect('mongodb://localhost:27017/test', callback);
});

The Mongo connection string or function can be used as the first argument of the constructor, or as part of an options object:

const milestoneDb = new MongoMilestoneDB({
  mongo: 'mongodb://localhost:27017/test',
  loggerLevel: 'debug',
});

Milestone snapshot saving

Intervals

By default, ShareDB will save a milestone snapshot with a given frequency. This library defaults to an interval of 1,000, saving milestones when the 1,000th, 2,000th, etc. versions are committed. That default interval can be configured:

const milestoneDb = new MongoMilestoneDB({
  mongo: 'mongodb://localhost:27017/test',
  interval: 500,
});

Complex saving logic

If you need more complex saving logic (eg different intervals depending on collection), this can be achieved using ShareDB middleware:

const milestoneDb = new MongoMilestoneDB('mongodb://localhost:27017/test');
const shareDb = new ShareDB({ milestoneDb: milestoneDb });

shareDb.use('commit', (request, callback) => {
  switch (request.collection) {
    case 'foo':
      // Save every 100 versions for collection 'foo'
      request.saveMilestoneSnapshot = request.snapshot.v % 100 === 0;
      break;
    case 'bar':
    case 'baz':
      // Save every 500 versions for collections 'bar' and 'baz'
      request.saveMilestoneSnapshot = request.snapshot.v % 500 === 0;
      break;
    default:
      // Don't save any milestones for collections not named here.
      // IMPORTANT: We have to set this to false to actively disable milestones
      // If left to null, then the default interval will still apply
      request.saveMilestoneSnapshot = false;
  }

  callback();
});

Note that the default value of request.saveMilestoneSnapshot is null. If left to this value, it will use the default interval logic. If you want to actively disable snapshots, you must make sure to set it to false.

Indexing

By default, indexing is enabled on the milestone collections in order to speed up fetching. This can have an adverse impact on performance if being enabled on an existing collection that is missing the index. The indexing can be disabled:

const milestoneDb = new MongoMilestoneDB({
  mongo: 'mongodb://localhost:27017/test',
  disableIndexCreation: true,
});

Error codes

5100 -- Internal error - DB

• 5101 -- Mongo closed