MongoDB using almost 50% memory usage

Ops and Admin
1

Hello Experts,
I am beginner to operate MongoDB and I have big challenge to handle/control host memory usage.
I run 3 replica mongoDB environment, each server has 125GB memory and 2 of them were using almost 50% of system memory which is almost 60GB out of 125GB. And I have no idea how to control the memory usage under 10GB.
So I am absolutely looking for somebody who can advise on above matter.

Will stay tuned and thanks in advance to whom give support on this matter.

2

See: https://docs.mongodb.com/manual/core/wiredtiger/#memory-use

With WiredTiger, MongoDB utilizes both the WiredTiger internal cache and the filesystem cache.

Starting in MongoDB 3.4, the default WiredTiger internal cache size is the larger of either:

50% of (RAM - 1 GB), or
256 MB.

Via the filesystem cache, MongoDB automatically uses all free memory that is not used by the WiredTiger cache or by other processes.

3

You can limit the size of WiredTiger internal cache by setting up storage.wiredTiger.cacheSizeGB parameter during mongod startup or in configuration file. Below is the snippet of a configuration file used in one of my deployment where i limit the internal cache to 8GB.

storage:
  dbPath: /ebs01/mongo/data/
  engine: wiredTiger
  directoryPerDB: true
  wiredTiger:
    engineConfig:
       cacheSizeGB: 8
       directoryForIndexes: true

Hope this helps.

Regards,
E