gistfile1.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using MongoDB.Bson;
using MongoDB.Driver;
using MongoDB.Driver.Builders;

namespace TestSlowGetMore
{
    class Program
    {
        static void Main(string[] args)
        {
            var server = new MongoClient("mongodb://localhost:30000,localhost:30001").GetServer();

            var db = server.GetDatabase("omni");

            var c = db.GetCollection<BsonDocument>("MyCollection");

            c.Drop(); // get rid of the data...
            InsertData(c);

            var query = Query.And(
                Query.Matches("category", "foo"),
                Query.Matches("refid", "bar"),
                Query.Exists("Topic_ID")
            );

            int count = 0;
            var cursor = c.Find(query);
            cursor.SetLimit(1000);

            foreach (var doc in cursor)
            {
                Console.WriteLine("i=" + (++count));
            }

            Console.WriteLine("Finished");
            Console.ReadKey();
        }

        private static void InsertData(MongoCollection<BsonDocument> collection)
        {
            var random = new Random();
            var categories = new [] { "foo", "other" };
            var refids = new [] { "bar", "other" };

            for (int i = 0; i < 10000; i++)
            {
                var doc = new BsonDocument
                {
                    { "category", categories[random.Next(0, categories.Length)] },
                    { "refid", refids[random.Next(0, refids.Length)] },
                    { "Topic_ID", true, random.Next(0,100) < 50 } // only include sometimes
                };

                collection.Insert(doc);
            }
        }
    }
}