[Owncloud] Background Jobs

[Jakob Sack]

Hi Jan,

thank you for the praise.
as far as I know there is no reason for completely disabling background 
jobs.
I strongly disaggree with you regarding your second argument. Using 
AJAX always is a bad idea. Exactly spoken, there are at least two 
problems with the ajax solution: if you installed ownCloud on a shared 
web hosting service and use it alone or with your family chances are 
high that there are periods with no one being online. Then you could 
miss news that are meant to be fetched every now and then. In this case 
a webcron serice would be perfect. On the other hand a large setup with 
several hundred users - we both know that they exist - should not be 
bombed with another hundred requests every minute. In this case it's 
better to use the systems cron service which does not have the 
limitations apaches processes might have.
regards,

Jakob

Am 11.08.2012 20:30, schrieb Jan-Christoph Borchardt:
> Awesoooome! Does that mean that step-by-step, all the »refresh« and
> »rescan« buttons can go away?
>
> Just one thing: You say »there are four options: using the systems
> cron feature, using a webcron service, using AJAX or not using
> background jobs at all.«
> Why even have the possibility to deactivate it? It’s a great function
> which improves the experience silently, as with doing away with the
> need for refresh buttons. And since doing it via AJAX is a good
> default there’s no reason to not just do it like that always – or is
> there?
>
>
> On Sat, Aug 11, 2012 at 7:07 AM, Jakob Sack <mail at jakobsack.de> 
> wrote:
>> Hi,
>>
>> yesterday I pushed the new Background Jobs system to ownCloud 
>> master. As you
>> can guess from the name, this feature allows ownCloud to do certain 
>> tasks in
>> the background without blocking the UI. It also makes it possible to 
>> execute
>> some tasks without any need of user interaction, for example 
>> fetching news
>> while the user is on holidays.
>> From a users perspective there is not much to pay attention to, 
>> background
>> jobs tries to get out of the way as much as possible. On the other 
>> hand,
>> administrators can use the settings interface to set the way 
>> background jobs
>> are executed. There are four options: using the systems cron 
>> feature, using
>> a webcron service, using AJAX or not using background jobs at all. 
>> Using the
>> systems cron feature is the preferred way. It allows regular 
>> executed jobs
>> without the limitations the web server may have. The second 
>> recommended
>> option is the webcron implementation. By registering your ownCloud 
>> cron.php
>> address at a webcron service like [1] you ensure that background 
>> jobs will
>> be executed regularly. Using AJAX is the default option, although 
>> the least
>> reliable. Every time a  user visits the page a single background job 
>> gets
>> executed. The disadvantage of this solution compared to the webcron 
>> service
>> is that it requires regular visits of the page. The reason for 
>> making this
>> option the default is that this solution simply does not require 
>> access to
>> the system or registration on some third party service.
>> When you are implementing background jobs in your app, please be 
>> aware of
>> the difference between the AJAX/Webcron and the cron implementation! 
>> The
>> AJAX/Webcron implementation gets started by 
>> your-favorite-web-server, so you
>> might have some limitations on execution time or memory. These 
>> limitations
>> do not affect the system cron implementation, which calls php from 
>> the
>> command line. As a consequence, you should split large tasks when 
>> not using
>> system cron. You can check whether the app has been started by 
>> systems cron
>> by checking if OC::$CLI is set to true.
>> If you want to  use background jobs in your app, you have to 
>> register them
>> in appinfo/app.php by calling OCP\BackgroundJobs::addRegularTask( 
>> $class,
>> $method ).
>> The first app featuring a background job is the news app being 
>> implemented
>> by Alessandro Cosentino (zimba12). If you want to use background 
>> jobs in
>> your app, have a look at the apps:newsapp repository first! There 
>> you will
>> not only find a working example, but also a strategy of how to deal 
>> with the
>> different requirements of AJAX/Webcron and the system cron.
>> Regards,
>>
>> Jakob
>>
>> 1: http://www.easycron.com/
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