Read preferences

Read preferences mongodb://mongo1.local,mongo3.local/?replicaSet=demo ⏎ &readPreference=secondary&readPreferenceTags=dc:europe

Servers: mongo1.local - primary - 6ms - dc:europe,server:big mongo2.local - secondary - 25ms - dc:europe,server:small mongo3.local - secondary - 4ms - dc:europe,server:big mongo4.local - secondary - 17ms - dc:europe,server:big mongo5.local - secondary - 16ms - dc:asia,server:big

Servers (after finding all candidates): mongo2.local - secondary - 25ms - dc:europe,server:small mongo3.local - secondary - 4ms - dc:europe,server:big mongo4.local - secondary - 17ms - dc:europe,server:big mongo5.local - secondary - 16ms - dc:asia,server:big

Servers (after matching tags): mongo2.local - secondary - 25ms - dc:europe,server:small mongo3.local - secondary - 4ms - dc:europe,server:big mongo4.local - secondary - 17ms - dc:europe,server:big

Servers (after sorting): mongo3.local - secondary - 4ms - dc:europe,server:big mongo4.local - secondary - 17ms - dc:europe,server:big mongo2.local - secondary - 25ms - dc:europe,server:small

Servers (after removing "far away" ones): mongo3.local - secondary - 4ms - dc:europe,server:big mongo4.local - secondary - 17ms - dc:europe,server:big And from those a random one per (read) query is picked.