Mongodb – the syntax of mongodump and mongorestore

MongoDB makes good use of your RAM. As long there is free RAM, it will take it. It will first try to get the indices into RAM. You can see their size with

use <yourDB>
db.status()

from the mongo shell.

Next it will try to keep as much as possible of your working set in RAM (which is a bit simplified, but sufficient for this explanation).

MongoDB does all this to improve performance, which is a good thing. It does not make much sense to have free RAM I'd,Ingrid around because it might be possible that some other process might need it in the future. It is much better to utilize the RAM available and free it on demand. Which is a bit of the discussion between Windows and UNIX memory usage patterns. Judging from that, I'd assume you run MongoDB on a Windows machine ;).

The spikes you are experiencing usually happen under more or less high load. As long as there is no impact on other processes, there is nothing to worry about. If other processes are impacted, I'd strongly suggest migrating them or MongoDB to a dedicated machine/instance/VM. Please read the MongoDB Production Notes for details on how to set up optimal machines for MongoDB.

I wasn't able to use wiredTiger upgrading MongoDB. However, at May 17 I uninstalled MongoDB 2.6 then installed MongoDB 3.0.3 . Immediate after the installation, I added storageEngine=wiredTiger on top of my mongod.conf file. Then I gave sudo service mongod start command and eventually I could.

Edit:

For fresh installed as directed by official documentation;

1. Open configuration file using sudo nano /etc/mongod.conf
2. Change the # engine line to engine: wiredTiger like the below
3. Run mongod using the command sudo service mongod start

.

# Where and how to store data.
storage:
  dbPath: /var/lib/mongodb
  journal:
    enabled: true
  engine: wiredTiger
#  mmapv1:
#  wiredTiger:

Edit:

If the current version is supported the wiredTiger;

1. Get the backup of the current database using mongodump command
2. Stop the mongod service using sudo service mongod stop command
3. Add storageEngine=wiredTiger text as the first line of mongod.conf file
4. Delete the all file on /var/lib/mongodb (or /data/db folder if used)
   [This is important. Because MongoDB cannot convert the current MMAP db files to wiredTiger format]
5. Start the mongod service using sudo service mongod start command
6. Restore the database from the backup using [mongorestore][2] command
7. wiredTiger is being used...