Feat; status page queries

[Jamesbarford]

This should have no performance bottle necks; Both in_progress and completed are obtained in 2 queries.

Roughly we have;

completed_requests: [ (request, duration, Vec<error>) ]

in_progress: [ (request, Vec<Job>) ]

Then in the website we'd compose the queue by calling the method from the job_queue module.

Annoyingly we don't have any database deserialisation so I've had to do it manually. The test probably gives the best example of why this approach is handy. I've tried to push all of the oddities into the postgres.rs file so nothing leaks out.

[Kobzol]

Thanks! It's a bit weird to encode the knowledge of status page data in the database crate, but I guess that it is better than splitting it into multiple methods on the pool, as we want to get highly specialized results here, and ideally in an optimal manner. So fine by me.

[Kobzol]

I thought about this a bit more and I think that we should probably just compute the request computation duration at completion time, and then just store it as a field in the benchmark request table. It will allow us to avoid doing this job query everytime we load the page, and it makes the duration immutable. If we load the jobs on every status page load, then if the jobs disappear, the duration can change (should be quite rare), but more importantly if we backfill the request in the meantime, then suddenly the duration of the request would jump to some ludicrously long duration, because we'd get a new recent completed job, while the old completed jobs could be e.g. 1-2 days old.

Computing the duration once at the time the request is completed (ideally in the mark_request_as_completed query) would avoid these, so I would prefer doing that.

[Kobzol]

Huh, interesting. The error count should be low, so normally I would just do a join and call it a day, but if this works, then why not.

[Jamesbarford]

Something to note on the error table is that it needs a unique "krate", aid pairing. Which if we are using for arbitrary error collection may mean we need think about this

[Kobzol]

Well, it's called "krate", but it's really just an arbitrary string, so we can put there "job-queue-error" or whatever.