distsys-nov-27th-2018.md

Hashtables, Viewstamped Repl, Raft (cont) - DistSys Lecture - Nov 27th, 2018

Healing a Partition

• The leader with the higher election term takes over according to the rules of Raft

Alternative: Run another election

Hints for using Raft on Project 4

• Build a library that sends and receives messages asynchronously
  • Have a goroutine send a message
• Make sure that two goroutines aren’t trying to send messages over the same TCP connection

One way to do timeouts

select {
	case <- tcpread():
		// try to read from connection for 3 seconds
	case <- time.After(3 * time.Second):
		// After 3 seconds, timeout
}

Viewstamped Replication (VR)

Hashtables

Keyspace partitioning

• Create an excessively large space (hashtable) and map nodes across the space randomly (literally assign each node a random number)

Adding new nodes

1. You give the new node a random number
2. Find the items the first node with a higher number than the new node and rehash values that will now be incorrectly hashed