Awesome
SYNOPSIS
A two-phase-commit protocol for leveldb.
DESCRIPTION
Provides strong-consistency for local-cluster replication.
Every node in your cluster can be writable and all reads from any node will be consistent.
Uses reconnect-core
to support an injectable transport for e.g. browser compatibility.
BUILD STATUS
SPECIFICATION
The algorithm for how this works is here
.
USAGE
EXAMPLE
SERVER A
var level = require('level');
var Replicator = require('level-2pc');
var net = require('net');
var db1 = level('./db', { valueEncoding: 'json' });
var opts = {
peers: [
{ host: 'localhost', port: 3001 },
{ host: 'localhost', port: 3002 }
]
};
var r = Replicator(db1, opts);
net.createServer(function(con) {
var server = r.createServer();
server.pipe(con).pipe(server);
}).listen(3000);
SERVER B
var opts = {
peers: [
{ host: 'localhost', port: 3000 },
{ host: 'localhost', port: 3002 }
]
};
var r = Replicator(db2, opts);
net.createServer(function(con) {
var server = r.createServer();
server.pipe(con).pipe(server);
}).listen(3001);
SERVER C
var opts = {
peers: [
{ host: 'localhost', port: 3000 },
{ host: 'localhost', port: 3001 }
]
};
var r = Replicator(db3, opts);
net.createServer(function(con) {
var server = r.createServer();
server.pipe(con).pipe(server);
}).listen(3002);
WRITE SOME DATA
Now go ahead and write some data to one of the servers and watch the data magically appear in the other servers!
setTimeout(function() {
db1.put('x', 100, function(err) {
console.log(err || 'ok');
});
setTimeout(function() {
db2.get('x', function() {
console.log(arguments);
db3.get('x', function() {
console.log(arguments);
});
});
}, 100);
}, 100);
TRANSPORT
When the server wants to connect to the peers
that have been specified, it defaults to using
tcp from the net
module. You can inject any
transportation layer you like by setting the
transport
property in the options object:
var net = require('net');
var opts = {
transport: function() {
return net.connect.apply(null, arguments);
},
peers: [ /* .. */ ]
};
var r = Replicator(db, opts);
API
Replicator(db, opts)
Returns a Replicator
object, which is an EventEmitter
.
-
db
leveldb database object -
opts
options object with the following properties:host
host that other peers should connect toport
port that other peers should connect topeers
an array of objects that specify the host and port of each peerminConsensus
how many peers must connect initially or respond to quorum
Replicator#createServer()
Returns a duplex rpc-stream
that can be served over e.g. http
or tcp
or any other transport supporting node streams.
Replicator#close()
Closes connections to all peers.
Event: 'ready'
Emitted when the replicator is ready to replicate with other peers. Happens when the replicator has enough connections for the quorum, i.e. when the number of peers is above minConsensus
.
Event: 'notready'
Emitted when the replicator is not ready to replicate with other peers. Happens when the replicator doesn't have enough connections for the quorum, i.e. when the number of peers goes below minConsensus
.
Event: 'connect'
Emitted when the replicator has connected to a peer.
host
host of the connected peerport
port of the connected peer
Event: 'error'
Emitted when there was an error in the connection between the replicator and a peer.
err
error object
Event: 'disconnect'
Emitted when the replicator has disconnected from a peer.
host
host of the disconnected peerport
port of the disconnected peer
Event: 'reconnect'
Emitted when the replicator tries to reconnect to a peer.
host
retrying connection to this hostport
retrying connection to this port
Event: 'fail'
Emitted when the replicator has tried to reconnect but failed too many times. There might be a problem with the connection, or the peer is simply offline.
host
host of the failing peerport
port of the failing peer