[p2pu-dev] Course metrics

[Alison Cole]

Hey Dirk, Although all of this is over my head I just want to let you know
how much I appreciate you posting these problem solving posts. I'm learning
a lot about programming by reading these and what you do behind the scenes!
Thanks for all your hard work being a one man show!

On Tuesday, June 19, 2012, Dirk Uys wrote:

> Hi everyone
>
> During the last release on 18 May I enabled course metrics for all course
> organizers believing that the metrics were working perfectly and that it's
> simply a permission update. You know what they say about assumption...
>
> The problem is that when a user goes to the metric page for a course the
> metrics get generated from the recorded page views (
> https://github.com/p2pu/lernanta/blob/master/lernanta/apps/tracker/models.py#L100).
> If the user refreshes the page (because it's taking so long), the process
> is started again and the metric updating procedure happens concurrently.
> This doesn't play nice with the intended use of the db and duplicated data
> is generated :(
>
> Now, solving this problem has multiple possibilities! Each with pros and
> cons.
>
> 1. Enforce some locking mechanism to ensure the operation only happens once
> + process doesn't run concurrently
> - user waits
> - lots of db work tied to specific requests
>
> 2. Queue a celery tasks that runs to operation
> + user doesn't need to wait for results
> - still need to implement some locking mechanism to prevent celery tasks
> from running concurrently
> - lots of db work tied to specific requests
>
> 3. Keep the table updated from the get go
> + metrics are always up to date
> - introduces small overhead to every page view
> - generate metrics that's never used
>
> 4. Fix the data duplication issue that presents itself
> + doesn't matter if process runs concurrently
> - update still takes a long time
> - lots of db work tied to specific requests
>
> 5. Don't trigger the update process based on user actions, but rather at a
> predetermined time
> + user doesn't wait
> - generate metrics that's never used
>
> 6. ?
>
> Does anyone have any thoughts on this?
>
> Cheers
> d
>


-- 

Alison
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