On 04/02/2012 09:49 AM, Matt Wagner wrote:
On Fri, Mar 30, 2012 at 11:59:11AM -0400, Tzu-Mainn Chen wrote:
https://www.aeolusproject.org/redmine/projects/aeolus/wiki/Allow_Conductor_t...
So I wrote the below email and was about to send it, when I realized that I'd focused on the technical implementation details without ever fully understanding the overall use case. But it's not abundantly clear to me what that entails. What information, exactly, are we intending to keep? I wonder if we should look at stashing core information in the Events table?
I'd imagine Hugh or someone else with a better feel for customer requirements may need to weigh in, but in general part of what we may be dealing with are audit requirements, especially if we ever start modeling cost issues. We may need to be able to produce a report on a user's history/activities, when instances were up, which ones, who changed properties, etc.
The "soft delete" vs. "archiving" is only part of this, though. We need it so that references in events, etc. to deleted items are still valid. However we also need to fully spec out the event/auditing requirements (not part of this task it seems). What changes do we need to record? What history do we need for what object types? Is there some process for purging in-db events/archives to some "long-term" storage/report format?
The document talks about two possible approaches to keeping deployment activity; one is to use an archive table, and another is to use a soft_delete flag. I'd be interested in hearing people's thoughts on both.
I was going to mention that I'm still fond of acts_as_paranoid, but I just saw your mention on the wiki page that Tomas sent a patch adding archivist six months ago. I'm all for just using that in this case. I think we're likely to need to stitch together associations anyway when we're dealing with deleted objects.
Though, FWIW, using soft delete wouldn't necessarily require any major changes. acts_as_paranoid would override the finder methods of AR to add a "WHERE deleted_at IS NULL" to all queries unless you ran "find_with_deleted". If we did this ourselves, we could probably just use a default scope and a with_deleted method to override it.
Yeah -- the document didn't make it clear whether you'd looked into the existing rails plugins for this, but when I looked into this a couple years ago there were options for both soft_delete (i.e. acts_as_paranoid) or archive tables (I forget what I found here). Also, while the finder overrides will make _most_ instances of deleted objects disappear, you've still got to be careful with joins, custom queries, etc. I'd imagine that even with acts_as_paranoid we'll need to be careful to make sure that our code doesn't find deleted stuff when we don't want it -- and that we've got decent automated test coverage to confirm that deleted things don't start appearing with future code changes.
The real pain with deletion isn't the object itself but the associations. Not just for query filtering (w/ soft-delete) but also w/ foreign key constraints (for 'archive tables').
Oh, and the document also talks about potentially using dbomatic for periodic history purges. I know there's been some discussion around dbomatic, so if someone had an opinion about that as well. . .
I think I talked to you on IRC about this and didn't note this objection, so I apologize for suddenly raising it. ;) But it occurs to me now that cleaning up old history is something that we want to do perhaps once a month, not every couple of minutes, so maybe we should just use cron. What if we added a rake task / little script that did this, using a configurable time period? Then we could ship with a reasonable default (do a monthly cleanup of entries older than 6 months?), but allow administrators to change it by just editing crontab. (I'm also not entirely convinced that deleting archived entries by default is a good thing... Some users might want to preserve history indefinitely. This way they could at least disable it easily.)
In addition, there may be other actions that need to occur in conjunction with purging history. Something as simple as a log file logging each deleted item (so there's still some possibility to manually recover old archive data if needed), or perhaps someting more complex. Also the 'deleted item' purging and old events purging should probably done in conjunction with each other.
One additional note -- the last sentence of your "Summary" section includes this interesting tidbit: "Finally, historical event data will need to be searched efficiently. In order to do so, we will evaluate Katello's search implementation and see if it is suitable."
With soft-delete, we've got search -- but perhaps even the standard list UI will help us -- we can provide an 'include deleted' flag for admins to see deleted stuff too.
That sounds like a really good idea, although I suspect it'll be a good bit of work, enough that I wonder if it should be its own feature. I think we'd need to work with Katello to make sure it was appropriately configured for multi-tenancy, and make sure that Katello and Aeolus both included a dependency on it, plus make sure that we had consistent configuration so that if one project set it up the other project could use it without problems. It's definitely achievable and likely worthwhile; I just think it deserves scoping as a bigger task. (IMHO.)
-- Matt