This document summarizes how to administer MongoDB using the command line interface. It discusses installing MongoDB, using basic commands like finding and saving documents, setting up replica sets for high availability and scaling, performing backups and repairs, and preventing slow queries through proper indexing. Sharding is mentioned as an advanced technique for scaling databases with large amounts of data or write operations.

1. Mongo Admin’ing
Jesse Wolgamott
twitter: @jwo slides: http://github.com/jwo

2. Quick Install
• Dev: brew install mongodb
• Server: apt-get install mongodb
• http://www.mongodb.org/display/
DOCS/Ubuntu+and+Debian+packages

3. Don’t Fear the
Command Line
Mongoid / Mongo Mapper
Ruby Driver
Command Line Javascript (mongo)

4. Quick Server Status
db
db.system.namespaces.find()
db.serverStatus()
db.currentOp()

5. Command Line Basics
use dba
db.collection.find({json params})
db.collection.findOne({json params})
db.collection.mapReduce(map,reduce)
db.collection.save({json})

6. Why Bother?
• Mongo queries enhance Mongoid queries
• Drop to command line when needed
• Game.where(:outcome=>{‘$in’=>[‘winning’
,‘tie’]})
• Game.collection.update({:outcome=>‘win
ning’, ‘$set’=>{:winning=>true}})

7. All Admin is
Command Line
• Setup Replica Sets
• Check on Status

8. Replica / Slave /
Journaling
“If you aren’t running a replica set, you don’t
care about your data”
-- Mongo DB dude

9. Master / Slave
What You’d Expect
M
Slave Slave Slave

10. Master / Slave
What You’d Expect
M Writes Go Here
Slave Slave Slave

11. Master / Slave
What You’d Expect
M Writes Go Here
Slave Slave Slave
Reads CAN Go
Here

12. Replica Sets
The new Hotness (and Recommended)
Primary Secondary Secondary Secondary
Arbiter

13. Replica Sets
The new Hotness (and Recommended)
Primary Secondary Secondary Secondary
Writes Go Here Arbiter

14. Replica Sets
The new Hotness (and Recommended)
Primary Secondary Secondary Secondary
Writes Go Here CAN Read Arbiter

15. Replica Sets
The new Hotness (and Recommended)
Primary Secondary Secondary Secondary
Writes Go Here CAN Read Arbiter
Nothing Goes
Here

16. Arbiter?
• Arbiters exist when even number of hosts
• They cast votes on primary elections
• Can exist on your app server

17. Journaling
• Added in 1.8
• mongod -- journal
• Will write out changes to a journal
directory
• You can restore from journal

18. Replica Set Fun
config = {
_id: 'houstonrb',
members: [
{_id: 0, host: 'localhost:20000'},
{_id: 1, host: 'localhost:20001'},
{_id: 2, host: 'localhost:20002', arbiterOnly: true}]
}
// Start it up
rs.initiate(config);
// Check it Out
rs.status()
// Who’s your daddy?
rs.isMaster()

19. Non-Master Reads
error: { "$err" : "not master", "code" : 10107 }
OK, so we’ll do:
db.getMongo().setSlaveOk()
// Awesome

20. Backup / Restore
mongodump --db houstonrb
mongorestore --db houstonrb -c
collections --drop --indexesLast
DirectoryName
* Have all your .bson files in a
directory named your database

21. Repairing
• The Data Gobbler -- mongodb likes hard-
drive space and won’t give it back
• Use mongod --repair to reclaim your
space!

22. Nightly Plan
service mongodb stop && mongod --repair --dbpath /var/
lib/mongodb && service mongodb start
rm -f /data/mongodump-backup.tar.bz2 && mongodump -
o /data/backups && tar -jcf /data/mongodump-
backup.tar.bz2 /data/backups && rm -rf /data/backups/

23. Catch Up!
• When a Replica Set gets ‘stale’
• rs.status will remain “5” (Recovering)
• On Master, will say “Error RS102 too stale
to catch up”
• stop mongo on all servers, copy over all
data files, including local.*, start all

24. Table Scans == Devil
• When you get to 500,000 records, your
DB may slow to crawl.
• /var/log/mongodb/mongodb.log for logged
queries (table scans)
• db.collection.getIndexKeys()
• Mongoid: rake
db:mongoid:create_indexes

25. No, Really
• I’ve been surprised LOTS at how often a
table scan happens.
• Test it out: mongod --notablescan
• Stuff will break.

26. Sharding
• Don’t Shard Early
• Helps in map-reduce
• You define a “shard-key”, like lastname
from A-H on this shard

27. Scaling (Secret Sauce)
• Many Shard Masters, even more slaves
• Add Shards for write and data size scaling
• Add Slaves for read scaling (map-reduce)
and redundancy
• Sharding is Hard

28. Neat Snippets
Replication Setup
Sharding Setup
https://github.com/mongodb/mongo-snippets

29. EC2 Notes
• Reformat drive to EXT4 or XFS
• Don’t use EBS for long term backups
• Can use EBS for setting up replica sets