What is a delayed background job? How does it work?

I am using Heroku to host a sm开发者_如何学Pythonall app. It's running a screenscraper using Mechanize and Nokogiri for every search request, and this takes about 3 seconds to complete.

Does the screenscraper block anyone else who wants to access the app at that moment? In other words, is it in holding mode for only the current user or for everyone?

If you have only one heroku dyno, then yes it is the case that other users would have to wait in line.

Background jobs are for cases like yours where there is some heavy processing to be done. The process running rails doesn't do the hard work up-front, instead it triggers a background job to do it and responds quickly, freeing itself up to respond to other requests.

The data processed by the background job is viewed later - perhaps in a few requests time, or whenever the job is done, loaded in by javascript.

Definitely, because a dyno is single threaded if it's busy scrapping then other requests will be queued until the dyno is free or ultimately timed out if they hang for more than 30 seconds.

Anything that relies on an external service would be best run through a worker via DJ - even sending an email, so your controller puts the message into the queue and returns the user to a screen and then the mail is picked up by DJ and delivered so the user doesn't have to wait for the mailing process to complete.

Install the NewRelic gem to see what your queue length is doing

John.

If you're interested in a full service worker system we're looking for beta testers of our Heroku appstore app SimpleWorker.com. It's integrated tightly into Heroku and offers a number of advantages over DJ.

It's as simple as a few line of code to send your work off to our elastic worker cloud and you can take advantage of massive parallel processing because we do not limit the number of workers.

Shoot me a message if you're interested.

Chad