Presentation given via webinar on 5th May 2010 by David Mytton on approaching 1 billion documents in MongoDB. Audio recording at http://bit.ly/mongo1bndocs

1. Approaching 1 Billion
Documents in MongoDB
David Mytton
1/25 david@boxedice.com / www.mytton.net

2. Server Density Monitoring
Processing Database UI
2/25
www.serverdensity.com

3. db.stats()
Documents 981,289,332
Collections 47,962
Indexes 39,684
Data size 369GB
Index size 241GB
3/25
As of 25th Apr 2010.

4. 10 months
4/25
Why we moved: http://bit.ly/mysqltomongo

5. Initial Setup
Replication
Master Slave
DC1 DC2
8GB RAM 8GB RAM
5/25

6. Vertical Scaling
Replication
Master Slave
DC1 DC2
72GB RAM 8GB RAM
6/25

7. Tip #1
Keep your indexes in
memory at all times.
db.stats()
7/25

8. Manual Partitioning
Replication
Master A Slave A
DC1 DC2
16GB RAM 16GB RAM
Replication
Master B Slave B
DC1 DC2
8/25 16GB RAM 16GB RAM

9. Database vs collections
• Many databases = many data files (small but
quickly get large).
• Many collections = watch namespace limit.
9/25

10. Namespaces = Number of collections +
number of indexes
10/25

11. Tip #2
Monitor the 24,000
namespace limit.
11/25

12. Using Server Density
12/25

13. Console
db.system.namespaces.count()
13/25

14. Replica Pairs = Failover
Replica Pair
Master A Slave A
DC1 DC2
16GB RAM 16GB RAM
Replica Pair
Master B Slave B
DC1 DC2
14/25 16GB RAM 16GB RAM

15. Tip #3
Pre-provision your oplog files.
15/25

16. A shell script to generate 75GB oplog files
for i in {0..40}
do echo $i
head -c 2146435072 /dev/zero > local.$i
done
16/25

17. Tip #4
Expect slower performance
during initial replica sync.
17/25

18. Tip #5
You can rotate your log files
from the console.
18/25

19. Rotating your log files
db.runCommand("logRotate")
19/25

20. Tip #6
Index creation blocks by
default. Use background
indexing if necessary.
20/25
MongoDB Manual: http://bit.ly/mongobgindex

21. Tip #7
Increase your OS file
descriptor limit + use
persistent connections.
21/25

22. Too many open files!
/etc/security/limits.conf
mongo hard nofile 10000
mongo soft nofile 10000
user type limit
/etc/ssh/sshd_config
UsePAM yes
22/25

23. Space is not reused
23/25

24. Tip #8
10gen commercial support is
worth paying for.
24/25

25. Summary
1. Keep indexes in memory.
2. Monitor the 24k namespace limit.
3. Pre-provision oplog files.
4. Expect slower performance on replica sync.
5. Rotate logs from the console.
6. Index creation blocks by default.
7. OS file descriptor limit + persistent connections.
25/25 8. Commercial support is worth it.