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level-jobs

Job Queue in LevelDB for Node.js

• Define worker functions
• Persist work units
• Work units are retried when failed
• Define maximum concurrency

Install

$ npm install level-jobs --save

Use

Create a levelup database

var levelup = require('levelup');
var db = levelup('./db')

Require level-jobs

var Jobs = require('level-jobs');

Define a worker function

This function will take care of a work unit.

function worker(id, payload, cb) {
  doSomething(cb);
}

This function gets 3 arguments:

• id uniquely identifies a job to be executed.
• payload contains everyting worker need to process the job.
• cb is the callback function that must be called when the job is done.

This callback function accepts an error as the first argument. If an error is provided, the work unit is retried.

Wrap the database

var queue = Jobs(db, worker);

This database will be at the mercy and control of level-jobs, don't use it for anything else!

(this database can be a root levelup database or a sublevel)

You can define a maximum concurrency (the default is Infinity):

var maxConcurrency = 2;
var queue = Jobs(db, worker, maxConcurrency);

More Options

As an alternative the third argument can be an options object with these defaults:

var options = {
  maxConcurrency: Infinity,
  maxRetries:     10,
  backoff: {
    randomisationFactor: 0,
    initialDelay: 10,
    maxDelay: 300
  }
};

var queue = Jobs(db, worker, options);

Push work to the queue

var payload = {what: 'ever'};

var jobId = queue.push(payload, function(err) {
  if (err) console.error('Error pushing work into the queue', err.stack);
});

or in batch:

var payloads = [
  {what: 'ever'},
  {what: 'ever'}
];

var jobIds = queue.pushBatch(payloads, function(err) {
  if (err) console.error('Error pushing works into the queue', err.stack);
});

Delete pending job

(Only works for jobs that haven't started yet!)

queue.del(jobId, function(err) {
  if (err) console.error('Error deleting job', err.stack);
});

or in batch:

queue.delBatch(jobIds, function(err) {
  if (err) console.error('Error deleting jobs', err.stack);
});

Traverse jobs

queue.pendingStream() emits queued jobs. queue.runningStream() emits currently running jobs.

var stream = queue.pendingStream();
stream.on('data', function(d) {
  var jobId = d.key;
  var work = d.value;
  console.log('pending job id: %s, work: %j', jobId, work);
});

Events

A queue object emits the following event:

• drain — when there are no more jobs pending. Also happens on startup after consuming the backlog work units.
• error - when something goes wrong.
• retry - when a job is retried because something goes wrong.

Client isolated API

If you simply want a pure queue client that is only able to push jobs into the queue, you can use level-jobs/client like this:

var QueueClient = require('level-jobs/client');

var client = QueueClient(db);

client.push(work, function(err) {
  if (err) throw err;
  console.log('pushed');
});

License

MIT