Hi Team,

In SERVER-38731 we introduced the ability to specify a parameter called initialSyncSourceReadPreference that allows one of the following options:

• primary
• primaryPreferred (Default for voting replica set members)
• secondary
• secondaryPreferred
• nearest (Default for newly added or non-voting replica set members)

I open this ticket to propose an improvement to this, allowing tag sets to be used for this parameter with the ability to configure replica set tags in order of preference just like when working with connection strings.

The reasoning is that this would allow users to control which replica set members are used as initial sync sources and avoid overloading members of the replica set that participate in low latency and/or critical operations. As an example, a user might want the initial sync overhead to be handled by Analytics nodes (MongoDB Atlas is a perfect example) or hidden nodes that do not interfere with low latency and/or critical workload.

This would affect the following versions:

• v4.2.7+
• v.4.4+
• v5.0+

Regards
Diego