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Before Start
The first thing to do will be get the information of out system:
- System Information: NMIS and OMK support tool will give us all the information needed.
- Monitor services: NMIS can monitor the involved processes - apache2, nmis9d, omkd and mongod - and provide useful information about CPU and memory - among others.
Number of processes
NMIS runs a daemon to obtain periodically the nodes information.
The number of workers is set in the parameter:
nmisd_max_workers
By default 10.
Some aprox. configurations:
Number of nodes | Number of threads |
---|---|
120 | 3-4 |
OMK has the equivalent parameter:
omkd_workers
Setting also omkd_max_requests, will help to have the threads restart gracefully before they get too big.
omkd_max_requests
MongoDB memory usage
MongoDB, in its default configuration, will use will use the larger of either 256 MB or ½ of (ram – 1 GB) for its cache size.
MongoDB cache size can be changed by adding the cacheSizeGB argument to the /etc/mongod.conf configuration file, as shown below.
storage: dbPath: /var/lib/mongodb journal: enabled: true wiredTiger: engineConfig: cacheSizeGB: 1
Here is an interesting information regarding how MongoDB reserves memory for internal cache and WiredTiger, the underneath technology. Also some adjustment that can be done: https://dba.stackexchange.com/questions/148395/mongodb-using-too-much-memory