allocator2: multi-metric allocation

[kvoli]

This issues tracks work on allocator2 package development, integration and testing.

Necessary for simulator integration

• [ ] Refactor asim to support hooking in different allocators
• [ ] Integrate allocator2 into asim simulator

Necessary for multi-metric rebalancing (non-centralized)

• [ ] Gossip IO
• [ ] Support rebalancing in allocator2 computeChanges()
• [ ] Separate out rebalancing and constraint satisfaction from the replicate queue
  • [ ] https://github.com/cockroachdb/cockroach/issues/90110
• [ ] Integrate allocator2 as a replacement for the store rebalancer
  • [ ] Add change dispatch handler local implementation
  • [ ] Add allocator2 handler, which periodically calls computeChanges and hands off changes to change dispatch.
  • [ ] Investigate concurrency handling (recv,send) snapshot queues.
• [ ] Evaluate allocator2 rebalancing performance for allocbench benchmarks

Necessary for recovery

• [ ] Support recovery in allocator2 computeChanges()

Dependencies on Allocator

• [ ] ShedLease used when draining node to iteratively remove leases.
• [ ] AllocateTargetFromList used for AdminRelocateRange to determine relocate operation order.
• [ ] AdminScatter used to semi-randomly rebalance replicas. See the scorer options maybeJitterStoreStats.

Necessary for centralized allocation

• [ ] Integrate communication
  • [ ] Protobufs for message structs
  • [ ] Hook up periodic load and problem range reporting
  • [ ] Add change dispatch handler remote implementation
• [ ] Add leader election support for electing centralized allocator

Jira issue: CRDB-27945

[kvoli]

Un-assigning myself for now. This project is currently unstaffed but may change in the future.