level-cowdown v1.0.0

level-cowdown

copy-on-write leveldown

example

We can make a lazy copy of the src database as the copy db:

var cow = require('level-cowdown');
var levelup = require('levelup');
var memdb = require('memdb');

var src = memdb({ valueEncoding: 'json' });
src.batch([
    { type: 'put', key: 'a', value: 100 },
    { type: 'put', key: 'b', value: 555 },
    { type: 'put', key: 'c', value: 300 },
], ready);

function ready () {
    var copy = levelup('fake', {
        db: function () { return cow(src, memdb()) },
        valueEncoding: 'json'
    });
    copy.get('a', function (err, value) {
        console.log('a:copy=', value);
    });
    copy.put('b', 5000, function (err) {
        src.get('b', function (err, value) {
            console.log('b:src=', value);
        });
        copy.get('b', function (err, value) {
            console.log('b:copy=', value);
        });
    });
}

output:

b:src= 555
a:copy= 100
b:copy= 5000

api

var cow = require('level-cowdown')

var copy = cow(originaldb, newdb)

Lazily make a copy of originaldb, storing data in newdb.

Returns a leveldown copy.

Note that if you modify originaldb, you will see those modifications in newdb unless newdb has operations on the same key.

install

With npm do:

npm install level-cowdown

license

MIT