[MB-63075] Collection aware DCP client for view engine

Product: Couchbase Server
Component: Data-Service
Issue Link: MB-63075
Affects Versions: 7.0.x, 7.1.x, 7.2.x, 7.6.x
Fix Version: 7.6.4

Summary

Prior to Couchbase Server 7.6.4, the View Engine makes use of a DCP consumer that is not aware of collections. This leads to the View Engine being unaware of collection-related changes occurring on a vBucket and only updates on changes to the default collections. This can result in the View Engine becoming too far behind the purge sequence number and entering a rollback loop due to the collections sequence numbers increasing.

This behaviour significantly affects cluster state change performance, such as graceful failover and rebalances.

Symptoms 

• Slow failover and rebalance performance with Views and collections deployed

Triggers

The requirements for this issue to be triggered are:

• Views deployed on a bucket
• The bucket views are deployed to make use of scopes and collections
• A failover or rebalance occurs

Verification

If a bucket has both Views and Scopes/Collections deployed, it is guaranteed to be impacted by the lack of collection awareness within the View Engine.

Workarounds

The only viable workaround for impacted rebalance performance due to the Views being present is to drop all Views present before the rebalance begins. These can then be created after the rebalance; however, during this period of time, any View Queries will fail.

All users of Views and Collections should upgrade to the latest 7.6 release as soon as possible.