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multi-master-merge

multi-master-merge

A database with multi master replication and merge support based on leveldb, fwdb and scuttleup

npm install multi-master-merge

build status

Usage

var mmm = require('multi-master-merge')
var level = require('level')
 
var mdb = mmm(level('data.db'), {encoding:'utf-8'})
 
mdb.put('hello', 'world', function(err, doc) {
  console.log('Inserted:', doc)
  mdb.get('hello', function(err, docs) {
    console.log('"hello" contains the following:', docs)
  })
})

When you do mdb.get(key, cb) you will always get an array of documents back. The reason for this is to support multi master replication which means that we might have multiple values for a given key.

Replication

To replicate your database simply open a sync stream and pipe it to another database

// a and b are two database instances 
var s1 = a.sync() // open a sync stream for db a 
var s2 = b.sync() // open a sync stream for db b 
 
s1.pipe(s2).pipe(s1) // pipe them together to start replicating 

Updates will now be replicated between the two instances. If two databases inserts a document on the same key both of them will be present if you do a mdb.get(key)

a.put('hello', 'a')
b.put('hello', 'b')
 
setTimeout(function() {
  a.get('hello', function(err, docs) {
    console.log(docs) // will print [{peer:..., value:'a'}, {peer:..., value:'b'}] 
  })
}, 1000) // wait a bit for the inserts to replicate 

Merging

To combine multiple documents into a single one use mdb.merge(key, docs, newValue) If we consider the above replication scenario we have two documents for the key hello

a.get('hello', function(err, docs) {
  console.log(docs) // will print [{peer:..., value:'a'}, {peer:..., value:'b'}] 
})

To merge them into a single document do

a.get('hello', function(err, docs) {
  a.merge('hello', docs, 'a + b')
})

Merges will replicate as well

// wait a bit for a to replicate to b 
b.get('hello', function(err, docs) {
  console.log(docs) // will print [{peer:..., value:'a + b'}] 
})

API

var mdb = mmm(db, [options])

Create a new database. db is a levelup instance. Options can include

{
  id: peerId, // defaults to a cuid 
  encoding: 'json' | 'utf-8' | 'binary', // the value encoding. defaults to binary 
  preupdate: function(logData, cb) {},  // set a preupdate hook 
  postupdate: function(logData, cb) {} // set a postupdate hook 
}

mdb.put(key, value, [cb])

Insert a new document. Callback is called with cb(err, doc) where doc is the inserted document.

mdb.get(key, cb)

Get documents stored on key. Callback is called with cb(err, docs).

mdb.createReadStream([options])

Get a stream of all {key:key, peer:peer, seq:seq, value:docs} pair in the database. You can pass in gt,gte,lt,lte options similar to levelup.

mdb.createKeyStream([options])

Similar to createReadStream but only returns keys

mdb.createLogStream([options])

Get a stream of all {key:key, value:doc} pairs in the log (all revisions of docs). Works about 10x faster than createValueStream, but returns all revisions, even merged ones.

mdb.merge(key, docs, newValue, [cb])

Merge multiple documents into a new document. Callback is called with cb(err, doc) where doc is the inserted merged document.

var stream = mdb.sync([options])

Returns a replication stream that can be piped to another mdb instance to replicate between them. Per defaults changes are replicated both ways. If you only want to push changes to another instance set {mode: 'push'} and if you only want to get changes do {mode: 'pull'}

mdb.fwdb

The used fwdb instance

mdb.log

The used scuttleup instance

License

MIT