Monitoring memory usage in WiredTiger
WiredTiger is MongoDB's default storage engine, known for its efficiency and scalability. When you initiate MongoDB with WiredTiger, it establishes an internal memory cache. How sizable is this cache? By default, it's roughly half of the RAM you have, minus 1 GB. Therefore, if you have 16 GB RAM the internal cache is set to about 7.5 GB. But that's not all the memory MongoDB uses. It also sets aside some memory for tasks such as handling connections and sorting data. MongoDB also takes advantage of any extra memory your system has to further improve its performance.
If you want to check or change the WiredTiger cache settings, you can use the MongoDB Shell. Using the parameter storage.wiredTiger.engineConfig.cacheSizeGB, lets you adjust the cache size.
Note
It's usually best to stick with the default cache size. But if your data is highly compressed, you may consider reducing the cache, say by 10-20% to free up some...
