couchdb-worker

CouchDB Worker

A worker module that manages state.

Installation

npm install couchdb-worker

Create a new Worker

Define an object with two functions: check and process:

var processor = {
  check: function(doc) {
    return true
  },
  process: function(doc, done) {
    // do something with the doc
    var output = {
      foo: 'bar'
    };
    done(null, output);
  }
}

The check function is called to decide whether this doc should be processed generally. For example you might only be interested in docs of a certain field. This function is the same as a filter function.

The processing takes place in the process function. This function takes two arguments: the doc and a callback function, done, which takes an error and the ouput of the processing when the job has been done. This output will be merged with the doc (if error is null) and saved. Note that the doc could have been changed after the job has been started so that the doc variable could differ from the doc when it gets saved.

The processor above inserts the property foo with the value bar into every document.

Also take a look at examples/.

Per Database Configuration

Configuration is done in a worker configuration document inside the target database. The worker looks at all databases and only process if there exists such a configuration file.

A Worker Configuration File might look like this:

{
  "_id": "worker-config/myworker",
  "_rev": "1-a653b27246b01cf9204fa9f5dee7cc64",
  "my_worker_setting": "100%"
}

You can update the config live so that all future processings will take the new configuration.

Worker Status Document

The worker stores a status document inside the target database. The worker stores its last update seq here and can resume at the point it has started the last processing.

{
  "_id": "worker-status/myworker",
  "_rev": "543-1922b5623d07453a753ab6ab2c634d04",
  "last_seq": 34176,
  "docs_processed": 145
}

Document Status Object

The worker updates a status object inside the document. This makes it supereasy to monitor worker status as well as it keeps a lock when many workers listen to the same database.

The status object of the worker could look like this:

"worker_status": {
  "worker-name": {
    "status": "completed"
  }
}

The status field can be triggered, completed or error.

The worker status is scoped by the worker name in order to have many workers processing the same document.

Running the Worker

To start, this needs either the following environment variables set:

export HOODIE_SERVER=http://example.org
npm start

or pass them to the commandline:

HOODIE_SERVER=http://example.org npm start

Testing

Testing is done with Mocha. Run the tests with

npm test

License & Copyright

(c) 2012 Johannes J. Schmidt, Berlin

Licensed under the Apache License 2.0.