MongoDB Replication

Presented at MongoDB Seattle Sept 2012.

Transcript

1. 1 Sridhar Nanjundeswaran, 10gen sridhar@10gen.com @snanjund
2. 2 • Introduction to Replica Sets • Developing with Replica Sets • Operational Considerations • Miscellaneous
3. Introduction to Replica Sets What is it? Configuration Options
4. 4 Node 1 Node 2 Node 3
5. 5 Node 1 Secondary Node 2 Secondary Node 3 Primary Replication Replication Heartbeat
6. 6 Node 1 Secondary Node 2 Secondary Node 3 Primary Heartbeat Primary Election
7. 7 Node 1 Secondary Node 2 Primary Node 3 Primary Heartbeat Replication
8. 8 Node 1 Secondary Node 2 Primary Node 3 Secondary Replication Heartbeat Replication
9. 9 • Priorities – Help control election – Secondary only • Slave Delay – Purposely delay replication • Hidden – Not seen as part client connection • Tagging
10. 10 • New in 2.0.0 • Control over where data is written to • Each member can have one or more tags e.g. • tags: {dc: "ny"} • tags: {dc: "ny",
 ip: "192.168",
 rack: "row3rk7"} • Replica set defines rules for where data resides • Rules can change without changing app code
11. 11 { _id : "mySet", members : [ {_id : 0, host : "A", tags : {"dc": "ny"}}, {_id : 1, host : "B", tags : {"dc": "ny"}}, {_id : 2, host : "C", tags : {"dc": "sf"}}, {_id : 3, host : "D", tags : {"dc": "sf"}}, {_id : 4, host : "E", tags : {"dc": "cloud"}}] settings : { getLastErrorModes : { allDCs : {"dc" : 3}, someDCs : {"dc" : 2}} } } > db.blogs.insert({...}) > db.runCommand({getLastError : 1, w : "allDCs"})
12. Developing with Replica Sets Consistency Write Preference Read Preference
13. 13 Primary Secondary Secondary Read Write Driver Client
14. 14 Primary Read Write Driver Read Secondary Secondary Client Application
15. 15 • Fire and forget • Wait for error • Wait for journal sync • Wait for replication
16. 16 Driver Primary write apply in memory
17. 17 Driver Primary getLastError apply in memory
18. 18 Driver Primary getLastError apply in memory write j:true Write to journal
19. 19 Driver Primary getLastError apply in memory write w:2 Secondary replicate
20. 20 • 5 modes – primary (only) - Default – primaryPreferred – secondary – secondaryPreferred – nearest
21. 21 • Custom read preferences • Control where you read from – E.g. { "disk": "ssd", "use": "reporting" } • Use in conjunction with standard read preferences – Except primary
22. Operational Considerations Upgrade/Maintenance Common Deployment Scenarios
23. 23 • No downtime • Rolling upgrade/maintenance – Start with Secondary – Primary last
24. 24 • Single datacenter • Single switch & power • Points of failure: – Power – Network – Datacenter – Two node failure • Automatic recovery of single node crash Member 1 Member 2 Member 3
25. 25 • Multi datacenter • DR node for safety • Can’t do multi data center durable write safely since only 1 node in distant DC Member 1 Member 2 Member 3 DC 1 DC 2
26. 26 • Three data centers • Can survive full data center loss • Can do w= { dc : 2 } to guarantee write in 2 data centers (with tags) Member 1 Member 2 Member 3 Member 4 DC 2 Member 5 - DR DC 1 DC 3
27. Miscellaneous Behind the scenes What’s new in 2.2
28. 28 • Local DB • Oplog – Capped collection – Idempotent version of operation stored db.replsettest.update({},{$inc:{set:1}}) { "ts" : …, "h" : …, "op" : "u", "ns" : "mongo_la.replsettest", "o2" : { "_id" : ObjectId("4f177bc768dad821278224d8") }, "o" : { "$set" : { "set" : 2 } } }
29. 29 • Full read preference support in mongos – Drivers too • Improved RS lag logging • rs.syncFrom command • buildIndexes setting • replIndexPrefetch setting
30. 30 • Use replica sets • Easy to setup even on a single machine • Check doc page for RS tutorials – http://docs.mongodb.org/manual/replication/#t utorials
31. 31 @mongodb © Copyright 2010 10gen Inc. conferences, appearances, and meetups http://www.10gen.com/events http://bit.ly/mongofb Facebook | Twitter | LinkedIn http://linkd.in/joinmongo download at mongodb.org We’re Hiring ! sridhar@10gen.com @snanjund