Foursquare did add more MongoDB servers, the problem was that the 5% of records that were migrated off of the full server were small, so the removal didn't resu

Foursquare did add more MongoDB servers, the problem was that the 5% of records that were migrated off of the full server were small, so the removal didn't result in many memory pages being released, so it didn't help. This article does not address how any of the alternatives address small records and rebalancing with small records.