[Tilesathome] Dissappearing tiles.

[spaetz]

> >They are not being thrown away, they will still be uploaded once they get
> >a slot in the upload queue.
> 
> Sloppy language on my part, sorry.

> Technically you are correct, but in reality, what is happening is that 1 tile request is being processed in full by up to 6 different clients,

Yes, that could happen, but only something like 30 hours after the first job has been handed out. These 30 hours would only apply if all our job queues were empty (in which case some redundancy wouldn't hurt). If queues are longer (as is the case now) a failed job will effectively be requeued, so it will take much longer until a rerender request is reissued. And if the upload happens while the rerender request is still in the pending queue it will be deleted.

So yes, while some redundancy can occur, I think it is not as bad, as a rerender request will sit and wait in our queue for quite some time, giving the uploaded tile some more time.

> Such a waste of processing power. Perhaps at times like these, it would be a good idea to throttle back the number of requests being given out to try and bring the upload queue under control?

Would be nice, and I did implement this with a "maximum active number of concurrent jobs" rate limiting. However it miserably failed as many requests fail to render and - as we don't have good failure feedback mechanisms - effectively clogged up the active job slots with failed jobs. This lead us to only have a handful of actually rendering clients at any one time. In order to improve this, we would need better failure feedback from clients to the server.

spaetz