Scylla consistency quiz for administrators¶
Topic: Architecture and development
Learn: Understanding consistency in Scylla: a quiz
Audience: Scylla administrators
Q: When you run
nodetool decommission to remove a node…
- Will the token range the node had will be relocated to other nodes? What about vnodes?
- When and how will we know the “decommission” operation is finished?
A1. Yes. The node enters the state “STATE_LEAVING” while streaming its data to other nodes. Then it is in “STATE_LEFT” when the data has been streamed.
nodetool netstats to check the state of a node.
Q: Let’s say I have a 16 node cluster using Network Topology Strategy across 2 data centers. The replication factor is 2 in each datacenter (DC1: 2, DC2: 2). If I write using a LOCAL_QUORUM, I will write the data to 4 nodes (2 in each data center) but when will the acknowledgement happen?
A: The quorum is local to the data center, so there will be 2 writes local and 2 reads local. Asynchronously the local coordinator will send the write to a remote coordinator but the local read and write don’t need it