Better concurrency control for upload scheduling

[mithrandi]

Bug #818854 address one possible cause of an upload scheduling meltdown. However, if a backend is down or otherwise unreachable for a sufficient period of time, there will still be a significant backlog of scheduled uploads; even though these will most likely not be scheduled for exactly the same time, there will likely be a significant number of uploads running concurrently, which could cause sufficient resource starvation to achieve meltdown, and is most likely undesirable even when it does not lead to a complete meltdown.

The correct approach for handling this is probably to control concurrency independently for each backend.

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Imported from Launchpad using lp2gh.

• date created: 2011-07-31T13:06:44Z
• owner: mithrandi
• the launchpad url was https://bugs.launchpad.net/bugs/818855