[OAK-4069] Use read concern majority when connected to a replica set

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.5.16, 1.6.0
• Component/s: mongomk
• Labels: resilience
• Epic Link: DocumentMK resilience
• Assignee: Tomek Rękawek
• Reporter: Tomek Rękawek
• Created: 26/Feb/16 09:17
• Updated: 19/Jun/17 08:31
• Resolved: 14/Dec/16 21:10

Description

Mongo 3.2 introduces new query option: readConcern. It allows to read only these changes that have been already committed to the majority of secondary instances.

It prevents stale reads - a situation in which a change has been committed on the primary (and read from it), but due to the network partition a new primary is elected and the change is rolled back.

We should use this new option (together with w:majority implemented in OAK-3554) when running Oak on MongoDB replica set.

References:

• Jepsen: MongoDB stale reads
• MongoDB documentation: Read Concern in

Issue Links

• is blocked by: OAK-4580 Update to Mongo Java Driver 3.2.x
• is related to: OAK-6366 Detect unsupported combination of read and write concern