A short deck used as talking points for 10gen's Internals webinar.

1. @mongodb @mdirolf http://www.mongodb.org/

2. How it Works
http://www.flickr.com/photos/tmh9/677919415/

3. BSON
{“hello”: “bson”}
x15 x00 x00 x00 x02 h e
l l o x00 x05 x00 x00
x00 b s o n x00 x00
http://bsonspec.org

4. Messages
• TCP/IP Wire Protocol
• Separate messages for
insert, update, query, get_more, delete, etc.
http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol

5. Anatomy of an insert
use foo;
db.test.insert({“hello”: “bson”});
message length request id response id op code (insert)
x67x00x00x0 xXXxXXxXX x00x00x00x xd2x07x00x00
0 xXX 00
reserved collection name document(s)
x00x00x00x00 f o o . t e s t x00 BSON({“hello”: “bson”})
http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol

6. Memory mapped
storage engine

7. Commands
db.foo.drop();
=
db.foo.runCommand({drop: "foo"});
=
db.$cmd.findOne({drop: "foo"});
=
db.$cmd.find({drop: "foo"}).limit(-1);

8. Query optimizer
find({x: 10, y: “foo”})
scan
terminate
index on x
index on y remember

9. Geohashing
(20, 10)
(0001 0100, 0000 1010)
0000 0010 0110 0100
(21, 9) 0000 0010 0110 0011
Problem: bit-flips (127 vs 128)

10. Replication
Replica sets
Master - slave
master slave
master
master slave
slave slave slave
master master
slave
slave master

11. Replication
• oplog - capped collection
• idempotent ($inc -> $set)

12. Auto-sharding
Shards
mongod mongod mongod
...
Config mongod mongod mongod
Servers
mongod
mongod
mongod
mongos mongos ...
client