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MongoDB: How it Works
The document discusses MongoDB and how it works. It includes information on BSON, the wire protocol for messages like insert and query, the anatomy of an insert message, how MongoDB uses memory mapped storage, commands like drop, the query optimizer using indexes, issues with geohashing, replication using replica sets and oplogs, and auto-sharding using config and mongos servers.
MongoDB: How it Works
- 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 WireProtocol • Separate messages for insert, update, query, get_more, delete, etc. http://www.mongodb.org/display/DOCS/Mongo+Wire+Protocol
- 5. Anatomy of aninsert 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 storageengine
- 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