An introduction tot

1. mongo*
Just what do those commands do?
By Russell Smith

2. /usr/bin/whoami
• Russell Smith
• Consultant for UKD1 Limited
• I Specialise in helping companies going through rapid growth;
• Code, architecture, infrastructure, devops, sysops, capacity planning, etc
• <3 MongoDB, Neo4j, MySQL, Riak, Gearman, Kohana, PHP, Debian, Puppet, etc...

3. Huh?
• MongoDB ships with a variety of CLI tools
• Some popular;
mongodump, mongorestore, mongostat, mongo
• Some less so;
mongosniff, mongoexport, mongoimport, bsondump, etc

4. Core

5. mongo
• Probably the most commonly used
• ‘Hidden’ gems;
• ~/.mongorc.js - will be executed by default
• --eval “some js” - evaluates Javascript and exits

6. mongo (cont.)
~ mongo test --eval "printjson(db.getCollectionNames())"
MongoDB shell version: 2.1.0-pre-
connecting to: test
[ "fs.chunks", "fs.files", "system.indexes", "system.profile", "test" ]
~ mongo test --quiet --eval "printjson(db.getCollectionNames())"
[ "fs.chunks", "fs.files", "system.indexes", "system.profile", "test" ]

7. ~/.mongorc.js
x = db.queue.count({state:4});
if (x > 0)
{
print('WARNING: ' + x + ' hung jobs');
}

8. ~/.mongorc.js
~ mongo
MongoDB shell version: 2.1.0-pre-
connecting to: test
WARNING: 2 hung jobs
>

9. mongod
• The server itself
• Useful:
• --fastsync - allows (much) faster starting of a replset member by
using a (recent) snapshot of a peer
• --keyFile - replset / sharding authentication file

10. mongos
• Sits in front of your shard servers and directs queries
• --keyFile

11. Common

12. mongodump
• Used to take backups
• Common options:
• --oplog
• -d
• -c

13. mongodump (cont.)
~ mongodump -d test -c queue -q "{state:4}"
connected to: 127.0.0.1
DATABASE: test
to
dump/test
test.queue to dump/test/queue.bson
2 objects

14. mongorestore
• Restores backups taken with mongodump
• Interesting options;
• --filter
• --oplogReplay
• Possible performance issues with custom (non ObjectId) _id

15. mongorestore (cont.)
mongorestore -d test -c queue --filter "{state:4}" dump/test/queue.bson
connected to: 127.0.0.1
Mon Sep 19 07:34:03 dump/test/queue.bson
Mon Sep 19 07:34:03
going into namespace [test.queue]
764 objects found
2 objects processed

16. mongostat
• Produces periodically updated stats
• Useful in watching server load & spotting general performance issues

17. Common Cursor Total
operations paging data size queues
fsync active
locked
flushes clients

18. mongostat (cont’d)
• Watch for;
• faults (page faults)
• idx miss (index btree page misses)
• locked (percentage of time globally locked)
• repl (it should normally be M or SEC)

19. Others

20. mongoexport
• Useful to export data for use with another database or program
• You may specify down to the field level using a filter if needed
• Can export as;
• JSON (default)
• CSV

21. mongoimport
• Imports data in to mongodb
• Currently supports importing;
• JSON
• CSV
• TSV

22. mongoimport (cont’d)
• Useful options include;
• --upsert - allows updating objects that exist already
(see --upsertFields)
• --headerline - if your CSV / TSV contains headers
• -f / --fields - specify field names

23. bsondump
bsondump test.bson --type json
{ "_id" :
ObjectId( "4e72f51414345f302b0eea2e" ),
• Convert bson -> json
"test" : 1 }
1 objects found

24. bsondump (cont.)
bsondump test.bson --type debug
--- new object ---
size : 36
_id
• Debug info:
type: 7 size: 17
test
type: 1 size: 14
etc

25. mongofiles
~ mongofiles put test.txt
connected to: 127.0.0.1
added file: { _id: ObjectId('4e761b07c21062d06b349819'), filename:
"test.txt", chunkSize: 262144, uploadDate: new Date(1316363015625),
md5: "d41d8cd98f00b204e9800998ecf8427e", length: 12256 }
done!

26. mongofiles (cont.)
~ mongofiles list
connected to: 127.0.0.1
test.txt
12256

27. mongotop
• New in 1.9
• Collection level load stats

28. mongosniff
• Used for sniffing the traffic between client / server
• Can forward traffic
• Only really useful for debugging...

30. mongo-perf
• Does not ship with mongodb
See : https://github.com/mongodb/mongo-perf
• I can’t compile it, but it probably works

31. Useful third party tools

32. tungsten replicator
mysql> create table foo(id int primary key, msg varchar(35));
Query OK, 0 rows affected (0.05 sec)
mysql> insert into foo values(1, 'hello from MySQL!');
Query OK, 1 row affected (0.00 sec)
> db.foo.find()
{ "_id" : ObjectId("4dc77bacad9092bd1aef046d"), "id" : "1", "data" :
"hello from MySQL!" }
• http://code.google.com/p/tungsten-replicator/
• http://code.google.com/p/tungsten-replicator/wiki/

33. automongobackup
• A port of the popular AutoMySQLBackup
• Rotates & compresses backups
• https://github.com/micahwedemeyer/automongobackup

34. mongolog
• Full query logging
• Uses mongosniff
• Will be on github soon

35. Other interesting projects
• Eliots Munin plugins : https://github.com/erh/mongo-munin
• gridfs-fuse : https://github.com/mikejs/gridfs-fuse

36. Further reading
• Tungsten with Mongo details
http://scale-out-blog.blogspot.com/2011/05/introducing-mysql-to-mongodb.html
• Javascript shell API
http://api.mongodb.org/js/current/
• Admin UI’s
http://www.mongodb.org/display/DOCS/Admin+UIs
• Hacking the shell
http://bit.ly/r2vghH

37. Questions?