Releasenote slow index build / index rebalance

Index service uses DCP to get the data from data service, for the purpose of index build. Here, data service acts as a DCP producer and index service acts as a DCP consumer.

At the time of starting the stream of data, DCP producer allows the consumer to specify whether it can consume the data in out of sequence order (i.e. OSO enabled consumer). The data service reserves a right to decide if the data is sent in sequence order, or out of sequence order. But if the consumer does not specify if it is OSO enabled, data service will send the data in sequence order.

As per performance experiments mentioned in MB-56346, OSO enabled index builds can experience slowness as compared to OSO disabled index builds. This fact needs to be "release noted".

In Couchbase Server version 7.2.0, indexing uses OSO enabled index builds only for building indexes on non-default scopes/collections.

Note: Index rebalance requires index movement from one node to the other, to achieve better load balancing in the cluster. To move the indexes, index service first builds the indexes on the destination nodes, and then deletes the indexes on the source node. As index rebalance uses index builds, overall index rebalance may also experience slowness if the DCP streams are OSO enabled.

Following command can be used to make index service disable the use of OSO:

curl -u <username:password> https://<indexer_ip>:19102/settings -X POST -d '{"indexer.build.enableOSO":false}'