2012 mongo db_bangalore_replication
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The document provides an introduction to MongoDB replica sets, including why they are used, how they are configured, and how data is replicated between nodes. It discusses how replica sets provide high availability and data redundancy. The document also covers operational considerations for replica sets such as primary election, replication, read and write preference settings, and consistency models for writes.
![> conf = {
_id : "mySet",
members : [
{_id : 0, host : "A”, priority : 3},
{_id : 1, host : "B", priority : 2},
{_id : 2, host : "C”},
{_id : 3, host : "D", hidden : true},
{_id : 4, host : "E", hidden : true, slaveDelay : 3600}
]
}
> rs.initiate(conf)
14](https://image.slidesharecdn.com/2012mongodbbangalorereplication-121107122532-phpapp02/85/2012-mongo-db_bangalore_replication-14-320.jpg)
![> conf = {
_id : "mySet”, Primary DC
members : [
{_id : 0, host : "A”, priority : 3},
{_id : 1, host : "B", priority : 2},
{_id : 2, host : "C”},
{_id : 3, host : "D", hidden : true},
{_id : 4, host : "E", hidden : true, slaveDelay : 3600}
]
}
> rs.initiate(conf)
15](https://image.slidesharecdn.com/2012mongodbbangalorereplication-121107122532-phpapp02/85/2012-mongo-db_bangalore_replication-15-320.jpg)
![> conf = {
_id : "mySet”,
members : [
{_id : 0, host : "A”, priority : 3},
{_id : 1, host : "B", priority : 2}, Secondary DC
{_id : 2, host : "C”}, Default priority = 1
{_id : 3, host : "D", hidden : true},
{_id : 4, host : "E", hidden : true, slaveDelay : 3600}
]
}
> rs.initiate(conf)
16](https://image.slidesharecdn.com/2012mongodbbangalorereplication-121107122532-phpapp02/85/2012-mongo-db_bangalore_replication-16-320.jpg)
![> conf = {
_id : "mySet”,
Analytics node
members : [
{_id : 0, host : "A”, priority : 3},
{_id : 1, host : "B", priority : 2},
{_id : 2, host : "C”},
{_id : 3, host : "D", hidden : true},
{_id : 4, host : "E", hidden : true, slaveDelay : 3600}
]
}
> rs.initiate(conf)
17](https://image.slidesharecdn.com/2012mongodbbangalorereplication-121107122532-phpapp02/85/2012-mongo-db_bangalore_replication-17-320.jpg)
![> conf = {
_id : "mySet”,
members : [
{_id : 0, host : "A”, priority : 3},
{_id : 1, host : "B", priority : 2},
{_id : 2, host : "C”},
{_id : 3, host : "D", hidden : true},
{_id : 4, host : "E", hidden : true, slaveDelay : 3600}
]
}
Backup node
> rs.initiate(conf)
18](https://image.slidesharecdn.com/2012mongodbbangalorereplication-121107122532-phpapp02/85/2012-mongo-db_bangalore_replication-18-320.jpg)
![{
_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"})
40](https://image.slidesharecdn.com/2012mongodbbangalorereplication-121107122532-phpapp02/85/2012-mongo-db_bangalore_replication-40-320.jpg)
2012 mongo db_bangalore_replication
- 1. Sridhar Nanjundeswaran, 10gen sridhar@10gen.com @snanjund October 26, 2012 1
- 2. • Introduction to Replica Sets • Developing with Replica Sets • Operational Considerations • Behind the Curtain 2
- 3. Introduction to Replica Sets Why? What is it? Configuration Options
- 4. • How many have faced node failures? • How many have been woken to do fail overs? • How many have experienced issues due to n/w latency? • Different uses for data – Normal processing – Simple analytics 4
- 5. Node 1 Node 2 Node 3 5
- 6. Node 1 Node 2 RS Init Node 3 6
- 7. Node 1 Node 2 Heartbeat Election Node 3 7
- 8. Node 1 Node 2 Secondary Heartbeat Secondary Node 3 Primary Replication Replication 8
- 9. Primary Election Node 1 Node 2 Secondary Heartbeat Secondary Node 3 Primary 9
- 10. Replication Node 1 Node 2 Secondary Heartbeat Primary Node 3 Primary 10
- 11. Replication Node 1 Node 2 Secondary Heartbeat Primary Node 3 Recovery 11
- 12. Replication Node 1 Node 2 Secondary Heartbeat Primary Node 3 Secondary Replication 12
- 13. Node 1 Node 2 Secondary Heartbeat Arbiterr Node 3 Primary Replication 13
- 14. > conf = { _id : "mySet", members : [ {_id : 0, host : "A”, priority : 3}, {_id : 1, host : "B", priority : 2}, {_id : 2, host : "C”}, {_id : 3, host : "D", hidden : true}, {_id : 4, host : "E", hidden : true, slaveDelay : 3600} ] } > rs.initiate(conf) 14
- 15. > conf = { _id : "mySet”, Primary DC members : [ {_id : 0, host : "A”, priority : 3}, {_id : 1, host : "B", priority : 2}, {_id : 2, host : "C”}, {_id : 3, host : "D", hidden : true}, {_id : 4, host : "E", hidden : true, slaveDelay : 3600} ] } > rs.initiate(conf) 15
- 16. > conf = { _id : "mySet”, members : [ {_id : 0, host : "A”, priority : 3}, {_id : 1, host : "B", priority : 2}, Secondary DC {_id : 2, host : "C”}, Default priority = 1 {_id : 3, host : "D", hidden : true}, {_id : 4, host : "E", hidden : true, slaveDelay : 3600} ] } > rs.initiate(conf) 16
- 17. > conf = { _id : "mySet”, Analytics node members : [ {_id : 0, host : "A”, priority : 3}, {_id : 1, host : "B", priority : 2}, {_id : 2, host : "C”}, {_id : 3, host : "D", hidden : true}, {_id : 4, host : "E", hidden : true, slaveDelay : 3600} ] } > rs.initiate(conf) 17
- 18. > conf = { _id : "mySet”, members : [ {_id : 0, host : "A”, priority : 3}, {_id : 1, host : "B", priority : 2}, {_id : 2, host : "C”}, {_id : 3, host : "D", hidden : true}, {_id : 4, host : "E", hidden : true, slaveDelay : 3600} ] } Backup node > rs.initiate(conf) 18
- 19. Developing with Replica Sets Consistency Write Preference Read Preference
- 20. Application Insert Read Primary v1 Secondary 20
- 21. Application 1 Insert Read Primary v1 Secondary Read Application 2 21
- 22. Application 1 Insert Read Primary v1 Secondary Does not Read exist Application 2 22
- 23. Application 1 Insert Read from primary is Read always consistent Primary v1 Secondary Read Application 2 23
- 24. Application 1 Insert Read Primary v1 Replicate Secondary v1 Read Application 2 24
- 25. Application 1 Insert Read Primary v1 Replicate Secondary v1 Read Read Application 2 25
- 26. Application 1 Insert Read Primary v1 Replicate Secondary v1 Reads V1 Read Read Application 2 26
- 27. Application 1 Insert Update Read Primary v1 v2 Replicate Secondary v1 Read Read Application 2 27
- 28. Application 1 Insert Update Read Read Primary v1 v2 Replicate Secondary v1 Read Read Application 2 28
- 29. Application 1 Insert Update Read Read Primary v1 v2 Replicate Secondary v1 Read Read Read Application 2 29
- 30. Application 1 Insert Update Read Read Primary v1 v2 Replicate Secondary v1 Read Read Read Application 2 30
- 31. Application 1 Insert Update Read Read Primary v1 v2 Replicate Replicate Secondary v1 v2 Read Read Read Application 2 31
- 32. Application 1 Insert Update Read Read Primary v1 v2 Replicate Replicate Secondary v1 v2 Read Read Read Read Application 2 32
- 33. Application 1 Insert Update Read Read Primary v1 v2 Replicate Replicate Secondary v1 v2 Read Read Read Read Application 2 33
- 34. • Fire and forget • Wait for error • Wait for journal sync • Wait for replication 34
- 35. Driver Primary write apply in memory 35
- 36. Driver Primary write getLastError apply in memory 36
- 37. Driver Primary write getLastError apply in memory j:true Write to journal 37
- 38. Driver Primary Secondary write getLastError apply in memory W:majority replicate 38
- 39. • Since 2.0.0 • Control over where data is written to • Each member can have one or more tags e.g. – Dc : "ny” – dc: "ny", ip: "192.168", rack: "row3rk7” • Replica set defines rules for where data resides • Rules can change without changing app code 39
- 40. { _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"}) 40
- 41. Driver Primary (sf) Secondary (ny) Secondary write (cloud) getLastError apply in memory W:allDCs replicate replicate 41
- 42. • 5 modes (new in 2.2) – PRIMARY(only) - Default – PRIMARYPREFERRED – SECONDARY (only) – SECONDARYPREFERRED – NEAREST 42
- 43. • Custom read preferences • Control where you read from – E.g. { "disk": "ssd", "use": "reporting" } • Use in conjunction with standard read preferences – Except primary 43
- 44. Operational Considerations Upgrade/Maintenance Common Deployment Scenarios
- 45. • No downtime • Rolling upgrade/maintenance – Start with Secondary – Primary last 45
- 46. • Single datacenter • Single switch & power Member 1 • Points of failure: – Power Member 2 – Network – Datacenter Member 3 – Two node failure • Automatic recovery of single node crash 46
- 47. • Multi datacenter DC Member 1 • DR node for safety 1 • Can’t do multi data Member 2 center durable write safely since only 1 node in distant DC DC Member 3 2 47
- 48. • Three data centers DC • Can survive full data Member 1 1 center loss Member 2 • Can do w= { dc : 2 } to guarantee write in 2 DC Member 3 2 data centers (with Member 4 tags) DC Member 5 - 3 DR 48
- 49. Behind the Curtain Schema Oplog
- 50. • Local DB (not replicated) – system.replset – oplog.rs • Capped collection • Idempotent version of operation stored 50
- 51. • Heartbeat every 2 seconds – Times out in 10 seconds • Missed heartbeat considered node down 51
- 52. > db.replsettest.insert({_id:1,value:1}) { "ts" : Timestamp(1350539727000, 1), "h" : NumberLong("6375186941486301201"), "op" : "i", "ns" : "test.replsettest", "o" : { "_id" : 1, "value" : 1 } } > db.replsettest.update({_id:1},{$inc:{value:10}}) { "ts" : Timestamp(1350539786000, 1), "h" : NumberLong("5484673652472424968"), "op" : "u", "ns" : "test.replsettest", "o2" : { "_id" : 1 }, "o" : { "$set" : { "value" : 11 } } } 52
- 53. > db.replsettest.update({},{$set:{name : ”foo”}, false, true}) { "ts" : Timestamp(1350540395000, 1), "h" : NumberLong("- 4727576249368135876"), "op" : "u", "ns" : "test.replsettest", "o2" : { "_id" : 2 }, "o" : { "$set" : { "name" : "foo" } } } { "ts" : Timestamp(1350540395000, 2), "h" : NumberLong("- 7292949613259260138"), "op" : "u", "ns" : "test.replsettest", "o2" : { "_id" : 3 }, "o" : { "$set" : { "name" : "foo" } } } { "ts" : Timestamp(1350540395000, 3), "h" : NumberLong("- 1888768148831990635"), "op" : "u", "ns" : "test.replsettest", "o2" : { "_id" : 1 }, "o" : { "$set" : { "name" : "foo" } } } 53
- 54. • Full read preference support in mongos – Drivers too • Improved RS lag logging • rs.syncFrom command • buildIndexes setting • replIndexPrefetch setting 54
- 55. • Use replica sets • Easy to setup – Try on a single machine • Check doc page for RS tutorials – http://docs.mongodb.org/manual/replication/#t utorials 55
- 56. download at mongodb.org We’re Hiring ! sridhar@10gen.com @snanjund conferences, appearances, and meetups http://www.10gen.com/events Facebook | Twitter | LinkedIn http://bit.ly/mongofb @mongodb http://linkd.in/joinmongo © Copyright 2010 10gen Inc. 56