MongoCursor<BsonDocument> converting to List is very slow

Question

 MongoCollection<BsonDocument> collection = db.GetCollection("TestCollection");
 MongoCursor<BsonDocument> cursor = collection.FindAll();
 List<BsonDocument> list = cursor.toList(); 

This is very slow executing. MongoCursor converting to a List is very slow, but if I use the following code:

MongoCollection<T> collection = db.GetCollection<T>("TestCollection");
MongoCursor<T> cursor = collection.findAll();
List<T> entities = cursor.toList(); 

The above code is much faster. Why is MongoCursor converting to a List so slow? I want to use BsonDocument. How can I solve this problem?

Answer 1

There's a bug with driver 1.8.0 ~ 1.8.2. We run into the same issue some days ago and reported in the MongoDb JIRA CSHARP-822. Upgrade to 1.8.3+ is supposed to resolve this issue.