The WiredTiger engine automatically closes and evicts idle tables in order to free cache space quickly. There are three knobs that can be adjusted to tune when and how often the file manager checks for idle tables.

• close_handle_minimum: number of handles open before the file manager will look for handles to close; default 250
• close_idle_time: amount of time in seconds a file handle needs to be idle before attempting to close it; default 30 secs
• close_scan_interval : interval in seconds at which to check for files that are inactive and close them; default 10 secs

The defaults should be increased in the MongoDB integration layer. This will result in the regular LRU eviction policy to control when collections are evicted from cache and is more in line with behavior most users expect.