----- Original Message -----
From: "Matt Wagner" matt.wagner@redhat.com To: "Tzu-Mainn Chen" tzumainn@redhat.com Cc: aeolus-devel@lists.fedorahosted.org Sent: Tuesday, April 3, 2012 11:53:22 AM Subject: Re: RFC Feature Planning: Deployment Activity History
On Tue, Apr 03, 2012 at 12:05:48AM -0400, Tzu-Mainn Chen wrote:
Thanks for the comments! My comments in-line:
----- Original Message -----
From: "Matt Wagner" matt.wagner@redhat.com To: "Tzu-Mainn Chen" tzumainn@redhat.com Cc: aeolus-devel@lists.fedorahosted.org Sent: Monday, April 2, 2012 9:49:02 AM Subject: Re: RFC Feature Planning: Deployment Activity History
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?
To be honest, I assumed that the scope of the task was simply to create a way to store events, and then worry about (potentially) adding events later. I'd hope that the implementation certainly wouldn't preclude that possibility, and expandability is definitely something worth keeping in mind.
So I certainly don't mean to point the finger at you here, because I think you're right about this task only referring to the technical changes. But I will note that this is the second major "Events" task to be entered without any user stories about what history we want to save, or why. Normally I'm not too big of a stickler about user stories, but in the case of storing events, I think it's really pretty important to know *what* we want to save. I suspect you've done the best that can be done without more background, but I think we could make more progress if we knew what it is that we're building.
No, that's a fair point. I'll update the doc and seek clarification.
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.
I personally prefer the soft delete approach, because my experience with playing with associations is not good; it's possible a bad association took my lunch money in grade school.
has_no :lunch_money ?
I think this is a good point, though. We have some code to check if things have the "last reference" to something on has_many relationships, which would probably result in things being deleted if we switched to archive tables.
Although, actually, we're still going to have to deal with this. Take deployments, which can't be deleted if they still have instances. (I'm going from memory here, so if that's not true, pretend it is.) Now if you "delete" all the instances, that code needs to be changed to look for non-deleted instances only, and to do a soft-delete on the deployment in that case. So I'm left wondering if maybe we're going to need to shape some code to suit our needs whether we use archive tables or soft deletes.
(Note, though, that I'm personally in the "soft delete" camp myself, I'm just thinking of ways to not reinvent the wheel after Tomas already sent out an archive table patch a few months ago.)
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.)
There's a separate task (specified in the document) that specifies that the administrator should be able to configure history purges. I should add details to that section to specify what I think that means. In any case, I disagree that cleaning up old history is a once-a-month task, but the point about cron still stands. What I *do* want to avoid is the sense that Conductor is using multiple schedulers for multiple tasks when one scheduler could do; I don't think that's a pleasant user experience. Ideally, though, the action and the scheduler should be reasonably discrete. I'll make a note of the issue in the documentation.
Oh, hmm -- does a "configurable policy" mean that you should be able to change it through the web interface? Because that potentially means that we can't "just use cron" here. Though I can see how being able to change this on the fly would actually be a bad thing -- someone accidentally changes the archive period to 1 hour, saves, loses almost all history, and then changes it back to 90 days and everyone is left wondering where the history went. (That said, I'm really not a big fan of disabling features because someone could misuse them. But it makes me wonder if maybe the interval should just be set in a config file, not on-the-fly.)
This might be a wider philosophical point, is the current standard to use a config file?
-- Matt