Cloned from launchpad blueprint https://blueprints.launchpad.net/nova/+spec/caching-scheduler.

Description:

I believe we need to encourage more scheduler innovation, by encouraging more scheduler drivers, allowing people to make different tradeoffs. Some of these may be dead ends, but I hope they may spark better ideas, and some may become the default scheduler, if they prove themselves.

This new driver attempts to:
* generate a list of pre-picked scheduler slots
* when user request hits scheduler, attempts to pick cached decision first

The idea is to do most of the expensive work up front, and do some very reduced filtering/weighting of hosts on each user request.

Implementation wise:
* this is a new driver
* uses the existing host manager for filtering and weighting
* will not have all the features of the existing filter scheduler

The current implementation is designed to work well under a low, but predictable load, when the cloud is also got a reasonable amount of space capacity.

Once this initial draft is complete (this blueprint), we can look at further ideas (in a follow up blueprint) to scale out the scheduler to multiple hosts with either:
* shared scheduler cache (centralised)
* pre-commit resources on a specific compute node's resource manager (de-centralised)

Specification URL (additional information):

None