multileveldown

multilevel implemented using leveldowns with seamless retry support

Usage

Similar to multilevel you can use this to share a levelup database across multiple processes over a stream. In addition multileveldown supports seamless retry so you can reconnect to a server without your read streams / puts failing etc.

First create a server:

const multileveldown = require('multileveldown')
const level = require('level')
const net = require('net')

const db = level('db')

const server = net.createServer(function (sock) {
  sock.on('error', function () {
    sock.destroy()
  })

  sock.pipe(multileveldown.server(db)).pipe(sock)
})

server.listen(9000)

Then create some clients:

const multileveldown = require('multileveldown')
const net = require('net')

const db = multileveldown.client()

const sock = net.connect(9000)
sock.pipe(db.connect()).pipe(sock)

db.put('hello', 'world', function () {
  db.get('hello', console.log)
})

Reconnect

To setup reconnect in your client simply set retry: true and reconnect to your server when the connection fails:

const multileveldown = require('multileveldown')
const net = require('net')

const db = multileveldown.client({
  retry: true
})

const connect = function () {
  const sock = net.connect(9000)
  const remote = db.connect()

  sock.on('error', function () {
    sock.destroy()
  })

  sock.on('close', function () {
    remote.destroy()
    setTimeout(connect, 1000) // reconnect after 1s
  })

  sock.pipe(remote).pipe(sock)
}

connect()

multileveldown will now make sure to retry your pending operations when you reconnect. If you create a read stream and your connection fails half way through reading that stream multileveldown makes sure to only retry the part of the stream you are missing. Please note that this might not guarantee leveldb snapshotting if you rely on that.

API

multileveldown.server(db, [options])

Returns a new duplex server stream that you should connect with a client. Options include:

{
  readonly: true, // make the database be accessible as read only
  preput: function (key, val, cb) {}, // called before puts
  predel: function (key, cb) {}, // called before dels
  prebatch: function (batch, cb) {} // called before batches
}

clientDb = multileveldown.client([options])

Creates a new client levelup that you can connect to a server. Options are forwarded to the levelup constructor.

clientDb.connect()

Returns a new duplex client stream that you should connect with a server stream

clientDb.createRpcStream()

Just an alias to .connect for multilevel API compatibility.

Install

With npm do:

npm i multileveldown

Contributing

Level/multileveldown is an OPEN Open Source Project. This means that:

Individuals making significant and valuable contributions are given commit-access to the project to contribute as they see fit. This project is more like an open wiki than a standard guarded open source project.

See the Contribution Guide for more details.

Donate

Support us with a monthly donation on Open Collective and help us continue our work.

License

MIT