{
    "in_latency_window": [], 
    "operation": "read", 
    "read_preference": {
        "mode": "Nearest", 
        "tag_sets": [
            {
                "data_center": "sf"
            }
        ]
    }, 
    "suitable_servers": [], 
    "topology_description": {
        "servers": [
            {
                "address": "b:27017", 
                "avg_rtt_ms": 5, 
                "tags": {
                    "data_center": "nyc"
                }, 
                "type": "RSSecondary"
            }, 
            {
                "address": "c:27017", 
                "avg_rtt_ms": 100, 
                "tags": {
                    "data_center": "nyc"
                }, 
                "type": "RSSecondary"
            }
        ], 
        "type": "ReplicaSetNoPrimary"
    }
}
