[CASSANDRA-3901] write endpoints are not treated correctly, breaking consistency guarantees

• Type: Sub-task
• Status: Resolved
• Priority: Normal
• Resolution: Duplicate
• Assignee: Peter Schuller
• Reporter: Peter Schuller

Authors

Peter Schuller

• Created: 13/Feb/12 00:47
• Updated: 16/Apr/19 09:32
• Resolved: 27/Sep/12 04:49

Description

I had a nagging feeling this was the case ever since I started wanting CASSANDRA-3833 and thinking about hot to handle the association between nodes in the read set and nodes in the write set.

I may be wrong (please point me in the direct direction if so), but I see no code anywhere that tries to (1) apply consistency level to currently normal endpoints only, and (2) "connect" a given read endpoint with a future write endpoint such that they are tied together for consistency purposes (parts of these concerns probably is covered by CASSANDRA-2434 but that ticket is more general).

To be more clear about the problem: Suppose we have a ring of nodes, with a single node bootstrapping. Now, for a given row key suppose reads are served by A, B and C while writes are to go to A, B, C and D. In other words, D is the node bootstrapping. Suppose RF is 3 and A,B,C,D is ring order. There are a few things required for correct behavior:

• Writes acked by D must never be treated as sufficient to satisfy consistency level since until it is part of the read set it does not count towards CL on reads.
• Writes acked by B must not be treated as sufficient to satisfy consistency level unless the same write is also acked by D, because once D enters the ring, B will no longer be counting towards CL on reads. The only alternative is to make the read succeed and disallow D from entering the ring.

We don't seem to be handling this at all (and it becomes more complicated with arbitrary transitions).

Issue Links

• relates to: CASSANDRA-3833 support arbitrary topology transitions