We have two MongoDB data nodes (replica set) - Primary & Secondary. I noticed that the non-mapped virtual memory is relatively high and wondering if they are hurting our MongoDB performance (The server usually peaked at around 6-7K queries per sec). In MMS, it was stated: "The most common case of usage of a high amount of memory for non-mapped is that there are very many connections to the database." So we checked the memory usage with db.serverStatus().mem in our Secondary: { "bits" : 64, "resident" : 6846, "virtual" : 416797, "supported" : true, "mapped" : 205549, "mappedWithJournal" : 411098, "note" : "virtual minus mapped is large. could indicate a memory leak" } Note: We are using 2.0.4 and now the default stack size should be 1MB per connection. The current number of connections is around 1.1K, but the non-mapped virtual memory (virtual-mappedWithJournal) is around 5699 MB. The trend is quite stable so I can't say there is a leak here, but where is the memory gone? Any idea?