couchdb-worker

CouchDB Worker

A worker module that manages state.

Installation

npm install couchdb-worker

Create a new Worker

new Worker(config, db)

Basically you define an object with two functions: check and process:

var Worker = require("couchdb-worker");

new Worker({
  name: 'myworker',
  server: "http://127.0.0.1:5984",
  processor: {
    check: function(doc) {
      return doc.type === 'post';
    },
    process: function(doc, done_func) {
      // Do work and call done_func callback with an error object
      // and the attributes to be merged into the doc.
      // You have access to the config document, see below.
      done_func(null, {
        foo: this.config.big_animal ? 'Bär' : 'bar'
      });
    }
  }
}, 'mydb');

This example processor inserts the property foo with the value bar or Bär, depending on the config document, into every document.

The processing takes place in the process function,

The return value of the check function decides wheather the worker is interested in a doc or not.

Run the Worker

npm start

Per Database Configuration

Configuration is done in a worker configuration document inside the target database.

The worker looks only processes if there exists such a configuration file.

A Worker configuration document might look like this:

{
  "_id": "worker-config/myworker",
  "_rev": "1-a653b27246b01cf9204fa9f5dee7cc64",
  "big_animal": true
}

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 where it left off.

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

Worker Options

name

Each worker needs a uniq name. It will be used for status objects and config - and status document ids.

server

The CouchDB server url.

processor.check

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 similar to a filter function.

CouchDB Worker will support Server Side Filters at some point in the future.

processor.process

This function takes two arguments: the doc and a callback function, done_func, which takes an error and the ouput of the processing when the job has been done. done_func also takes a status object as a third argument, which will be used to set the worker status if present. See lib/attachments-worker.js.

This output will be merged (using jQuery like deep extend) with the doc (if error is null) and saved.

config_id

The id of the configuration document. Default is worker-config/<worker-name>.

status_id

The id of the status document. Default is worker-status/<worker-name>.

batch_size

Number of changes to keep in RAM. Higher value means less HTTP requests but higher memory consumption.

Default is 10.

timeout

Number of miliseconds for timeout the changes feed. Defaults to 60000.

since

update_seq to initially start listening. Default is 0.

Conflict Resolution

Note that the doc could have changed after the job has been started so that the doc can not be saved. In that case CouchDB Worker will reset its worker state. The document will again show up in the changes feed an processed again.

Future versions of CouchDB Worker will provide a resolve conflict callback, where you can resolve that conflict in order to keep your heavy computed output.

Also take a look at examples.

Testing

Testing is done with Mocha.

npm test

License & Copyright

(c) null2 GmbH, 2012

License: The MIT License