Delayed methods

[Barry]

Hi, I faced such issue - my app should run some delayed method.

For example, I have Test model, which User can create. But to other users it should be visible only if it has :saved value in status attribute, which is assigned with special button.

I want to delete all tests, which remained unpublished 24 hours after creating.

And really don't know where to start. Found Rails episode 'Delayed Jobs', but it is not what I'm looking for, it is mostly about background methods.

Can you give me any keys to topic, from where I can begin digging by myself?

[Colin Law]

You could write a rake task to do the work and then run that from cron
daily or hourly or whatever is appropriate.

Colin

[Jodi Showers]

for regularly scheduled jobs, I use a mixture of cron (to create a delayed job), and the delayed_job itself

the crontab instance is very light, just a small (non-rails) rb script to insert the delayed_job in the delayed_jobs table

then the delayed_job instance will pickup the job and run it

in your instance, I would create a class method on the Test model - something like

def self.remove_old_unpublished

  delete_all(["created_at < ? and state in('unpublished')", 24.hours.ago])

end

cron entry like this:
05 1 * * * cd /path/to/current && RAILS_ENV=production /path/to/current/lib/delayed_job_cron_jobs/create_delayed_job.rb --model "Test" --method "remove_old_unpublished" --queue "general" --arguments "{:any_argument => 42}"

the following gist is a script to insert delayed_jobs from cron

https://gist.github.com/jshow/5228049

fyi, the reason to take this route over the simpler rake route (run rake task from cron) is performance and memory usage - this method will save you a bunch of both.

Jodi

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[Colin Law]

On 23 March 2013 15:15, Jodi Showers <jo...@homestars.com> wrote:
> for regularly scheduled jobs, I use a mixture of cron (to create a delayed
> job), and the delayed_job itself
>
> the crontab instance is very light, just a small (non-rails) rb script to
> insert the delayed_job in the delayed_jobs table
>
> then the delayed_job instance will pickup the job and run it
>
> in your instance, I would create a class method on the Test model -
> something like
>
> def self.remove_old_unpublished
> delete_all(["created_at < ? and state in('unpublished')", 24.hours.ago])
> end
>
> cron entry like this:
> 05 1 * * * cd /path/to/current && RAILS_ENV=production
> /path/to/current/lib/delayed_job_cron_jobs/create_delayed_job.rb --model
> "Test" --method "remove_old_unpublished" --queue "general" --arguments
> "{:any_argument => 42}"
>
> the following gist is a script to insert delayed_jobs from cron
> https://gist.github.com/jshow/5228049
>
> fyi, the reason to take this route over the simpler rake route (run rake
> task from cron) is performance and memory usage - this method will save you
> a bunch of both.

I am always suspicious of the idea of doing something in a more
complex way in order to save resources. It is only worth spending the
additional time developing the solution if computing resources are
likely to be an issue. Computing resources are usually cheaper than
human resources.

Colin

[Jodi Showers]

that is a good thinking, just like normalization - then comes a time to denormalize

we have millions of visitors per month - and about 50 asynch processes - having one rails process deal with all those asynchs rather than one per is not helpful in any way

using a best practice such as my approach is not harder to implement and will scale - choosing an approach of equal complexity that won't scale doesn't hold water

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[tamouse mailing lists]

Please bottom post (appending). It makes responses easier to find.

If you're working in a distributed, multi-server and multi-process
environment, cron is a poor solution. DelayedJobs and several others
work in a distributed environment much better. I have been using the
gem clockwork in addition to DJ, which makes things very simple.

[Jodi Showers]

I'm just about to scale to a second app server - so good timing

in which ways did you find cron to be a poor choice ? on a single server they meet our needs nicely

you'd only run one clock instance per cluster - so much like cron (ie. no interserver clock scheduling). Have you tried using clock driven from a schedule described in the db (like a centralized cron, useful for failover) ?

Any thoughts you have on this topic appreciated

As for the OP, I hope they can see the short and long term options before them.

J

[tamouse mailing lists]

The primary issue when you bring in multiple servers is
synchronization of the workers. Cron can't do that, as it only knows
about one server. Having something that workers can distribute over
requires something more sophisticated. That's what DJ is really about.
Using clockwork makes it all the easier coming from cron.

[Jodi Showers]

yes - I know - I use DJ presently

my question was about what advantages you see with clockwork over cron - other than syntax I don't see any advantages

now if the schedule was stored in the db, and I could run multiple clockworks on each server there would some inherent scheduling failover (DJ already provides job/worker failover)

[Colin Law]

On 23 March 2013 21:37, tamouse mailing lists <tamous...@gmail.com> wrote:
> ...

> The primary issue when you bring in multiple servers is
> synchronization of the workers. Cron can't do that, as it only knows
> about one server. Having something that workers can distribute over
> requires something more sophisticated. That's what DJ is really about.
> Using clockwork makes it all the easier coming from cron.

Since all the OP is trying to do (I believe) is run a task
occasionally to purge obsolete data from the database are those issues
actually a problem?

Colin

[tamouse mailing lists]

Since the person I was answering directly asked about scaling to
multipler servers, I'd say yes.

[tamouse mailing lists]

This is a bottom post. Please follow suit.

On Sat, Mar 23, 2013 at 4:47 PM, Jodi Showers <jo...@homestars.com> wrote:
> yes - I know - I use DJ presently
>
> my question was about what advantages you see with clockwork over cron -
> other than syntax I don't see any advantages

The advantage is that you'd need to be running cron on each of your
servers managing workers, whereas clockwork only needs to run on one
to keep things synchronized.

> now if the schedule was stored in the db, and I could run multiple
> clockworks on each server there would some inherent scheduling failover (DJ
> already provides job/worker failover)

If you do decide to go that route, DJ can handle the requeuing itself,
not needing anything else. It's just a bit more configuration and
such.

[Jordon Bedwell]

As much as I've seen you ask people not to top post, I'm going to
remind you to trim your emails, nobody wants to read 10 miles worth of
quotes when you could simply trim it, like I did...

[Colin Law]

I understand that it is relevant to Jodi's problem, I was enquiring
whether it is also relevant in the case described by the OP.

Colin