pouchdb-load

PouchDB Load

Client-side tools for loading a dump from a CouchDB/PouchDB database.

For dumping, check out pouchdb-dump-cli to dump from the command line, or pouchdb-replication-stream to dump from within your Node.js application.

This method is typically much faster than standard replication, because it uses fewer HTTP requests. So it's a great way to quickly load an initial state for your database.

Usage

To use this plugin, include it after pouchdb.js in your HTML page:

<script src="pouchdb.js"></script>
<script src="pouchdb.load.js"></script>

Or install from Bower:

bower install pouchdb-load

Or to use it in Node.js, just npm install it:

npm install pouchdb-load

And then attach it to the PouchDB object:

var PouchDB = require('pouchdb');
PouchDB.plugin(require('pouchdb-load'));

API

This plugin exposes a single method on your database, load():

db.load(urlOrString [, options] [, callback])

This method returns a Promise or calls your callback, if you prefer the callback style.

You can give it a URL pointing to a single dump file:

var db = new PouchDB('my-awesome-db');
db.load('http://example.com/my-dump-file.txt').then(function () {
  // done loading!
}).catch(function (err) {
  // HTTP error or something like that
});

This will read the entire file into memory, though. Assuming you used the --split option when you dumped your database, you can also load multiple files by using Promise.all. For instance, let's say you had 5 files, named 'my-dump-file_00000000.txt' through 'my-dump-file_00000004.txt'. You would do:

var dumpFiles = [
  'my-dump-file_00000000.txt',
  'my-dump-file_00000001.txt',
  'my-dump-file_00000002.txt',
  'my-dump-file_00000003.txt',
  'my-dump-file_00000004.txt',
];

PouchDB.utils.Promise.all(dumpFiles.map(function (dumpFile) {
  return db.load('http://example.com/' + dumpFile);
})).then(function () {
  // done loading!
}).catch(function (err) {
  // HTTP error or something like that
});

This will load them all simultaneously. You can also load them all in a series:

var series = PouchDB.utils.Promise.resolve();

dumpFiles.forEach(function (dumpFile) {
  series = series.then(function () {
    return db.load('http://example.com/' + dumpFile);
  });
});

series.then(function () {
  // done loading!
}).catch(function (err) {
  // HTTP error or something like that
});

Loading from a string rather than a URL

Instead of a URL, you can also load directly from a string. This is useful if you used pouchdb-replication-stream to dump directly to a string, or if you are loading your dumpfile through some other mechanism than ajax (websockets, WebRTC, etc.):

var db = new PouchDB('my-awesome-db');
var myDumpedString = getDumpedStringSomehow();

db.load(myDumpedString).then(function () {
  // done loading!
}).catch(function (err) {
  // any possible errors
});

Handoff to regular replication

Normally the load() operation doesn't write any checkpoints, meaning that if you switch from load() to normal replication, then it will start reading all the changes from the remote CouchDB from the beginning of time. This is slow, so to avoid it, use the proxy option:

db.load('http://example.com/my-dump-file.txt', {
  proxy: 'http://mysite.com/mydb'
}).then(function () {
  // done loading! handoff to regular replication
  return db.replicate.from('http://mysite.com/mydb');
}).catch(function (err) {
  // HTTP error or something like that
});

This will tell the plugin that the dumpfile 'http://example.com/my-dump-file.txt' is just a proxy for 'http://mysite.com/mydb'. So when you pick up replication again, it won't start from 0 but rather will start from the last checkpoint reported by the dump file.

If your replication also involves a filter function, you should pass that in as filter as well (so that the correct checkpoint can be written):

function filterFun(doc) {
  /* your cool filter function here */ 
}

db.load('http://example.com/my-dump-file.txt', {
  proxy: 'http://mysite.com/mydb',
  filter: filterFun
}).then(function () {
  // done loading! handoff to regular replication
  return db.replicate.from('http://mysite.com/mydb', {filter: filterFun});
}).catch(function (err) {
  // HTTP error or something like that
});

The same goes for view and query_params.

Custom ajax options

You can also include ajax options in the options:

db.load('myfile.txt', {
  ajax: {
    timeout: 30000
  }
});

The ajax options themselves are described in the PouchDB documentation.

Live demo

NPM Browser uses pouchdb-load to load a bunch of static files from Amazon S3, which is how it's able to replicate all of NPM so quickly. Here is the relevant code, which does the dump, checkpointing, and handoff to regular replication (as described above).

Notes on idempotency

The load() operation is idempotent, meaning that you can run it over and over again, and it won't create duplicate documents in the target database.

However, it's inefficient to run the load() every time the user starts your app. So if you'd like, you can use "local documents" to remember whether or not this database has already been loaded:

db.get('_local/initial_load_complete').catch(function (err) {
  if (err.status !== 404) { // 404 means not found
    throw err;
  }
  db.load(/* ... */).then(function () {
    return db.put({_id: '_local/initial_load_complete'});
  });
}).then(function () {
  // at this point, we are sure that 
  // initial replication is complete
}).catch(function (err) {
  // handle unexpected errors
});

This code first checks for a local document called '_local/initial_load_complete'. If the document is not found, then it calls dump(), then puts the local doc to mark that it's complete. Else it finishes.

(Local documents are non-replicated PouchDB/CouchDB documents that are useful for storing local state or configuration files. To create a local document, you simply prefix '_local/' to the document _id.)

Building

npm install
npm run build

Testing

In Node

This will run the tests in Node using LevelDB:

npm test

You can also check for 100% code coverage using:

npm run coverage

In the browser

npm run test-local

To test in your own browser, or

npm run test-browser

To test in PhantomJS.