How to increase the size of the MongoDB cache?
Via the filesystem cache, MongoDB automatically uses all free memory that is not used by the WiredTiger cache or by other processes. To adjust the size of the WiredTiger internal cache, see storage.wiredTiger.engineConfig.cacheSizeGB and –wiredTigerCacheSizeGB. Avoid increasing the WiredTiger internal cache size above its default value.
How does MongoDB keep data files in memory?
The storage.wiredTiger.engineConfig.cacheSizeGB limits the size of the WiredTiger internal cache. The operating system will use the available free memory for filesystem cache, which allows the compressed MongoDB data files to stay in memory.
Is there a deprecated storage engine in MongoDB?
Starting in version 4.2, MongoDB removes the deprecated MMAPv1 storage engine. Yes. See: The ratio of compressed data to uncompressed data depends on your data and the compression library used.
What should I do if I have multiple MongoDB instances?
If a single machine contains multiple MongoDB instances, then you should decrease the setting to accommodate the other mongod instances.
How is data represented in WiredTiger internal cache?
Different representations are used for data in the WiredTiger internal cache versus the on-disk format: Data in the filesystem cache is the same as the on-disk format, including benefits of any compression for data files. The filesystem cache is used by the operating system to reduce disk I/O.
What to do if mongod is not running in a container?
If you run mongod in a container (e.g. lxc , cgroups, Docker, etc.) that does not have access to all of the RAM available in a system, you must set storage.wiredTiger.engineConfig.cacheSizeGB to a value less than the amount of RAM available in the container. The exact amount depends on the other processes running in the container. See memLimitMB.