[CASSANDRA-6218] Repair should allow repairing particular data centers to reduce WAN usage

• Type: New Feature
• Status: Resolved
• Priority: Low
• Resolution: Fixed
• Fix Version/s: 2.0.4
• Component/s: Legacy/Tools
• Assignee: Jimmy Mårdell
• Reporter: Sankalp Kohli

Authors

Jimmy Mårdell

Reviewers

Lyuben Todorov

• Created: 18/Oct/13 20:45
• Updated: 16/Apr/19 09:32
• Resolved: 03/Dec/13 15:25

Description

The way we send out data that does not match over WAN can be improved.
Example: Say there are four nodes(A,B,C,D) which are replica of a range we are repairing. A, B is in DC1 and C,D is in DC2. If A does not have the data which other replicas have, then we will have following streams
1) A to B and back
2) A to C and back(Goes over WAN)
3) A to D and back(Goes over WAN)
One of the ways of doing it to reduce WAN traffic is this.
1) Repair A and B only with each other and C and D with each other starting at same time t.
2) Once these repairs have finished, A,B and C,D are in sync with respect to time t.
3) Now run a repair between A and C, the streams which are exchanged as a result of the diff will also be streamed to B and D via A and C(C and D behaves like a proxy to the streams).

For a replication of DC1:2,DC2:2, the WAN traffic will get reduced by 50% and even more for higher replication factors.

Issue Links

• is related to: CASSANDRA-6440 Repair should allow repairing particular endpoints to reduce WAN usage.