Mongo Java driver and replication tags

[Andy.Fan]

I added some tags in our mongo replication set like http://docs.mongodb.org/manual/tutorial/configure-replica-set-tag-sets/, then our application uses tags like 

cms.config.need.query.tag.normal=query:normal

cms.config.need.query.tag.regex=query:regex

I guess the tags are used by Java driver to choose which instance to request rather than mongo server decide which instance to server a request. 

So I want to know how does java driver use their tags, for example, What if the query is send without a tag while all the instances are tagged? What if the query with a tag, but the host with that tag is not available at that time?

It's be great that you can point the related Java class in Java driver. 

[Ross Lawley]

Hi,

Read preferences can be set at the MongoClient, Database, Collection or on a query by query basis and its part of the driver code to handle the server selection for a given request.

There is a specification regarding sever selection available here https://github.com/mongodb/specifications/blob/master/source/server-selection/server-selection.rst and the Java driver adheres to that specification.

Ross