Basic Replication in MongoDB
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This document discusses MongoDB replication and replica sets. It begins with an overview of why replication is useful, including protecting against node failures, network latency, and having different uses for data. It then covers the lifecycle of a replica set from creation to recovery. It describes the different roles nodes can have in a replica set and how replica sets are configured. It discusses considerations for developing applications with replica sets, including write acknowledgement and consistency levels. Finally, it covers some operational considerations like maintenance, upgrades, and topology options for replica sets spanning multiple data centers.
![> 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)
Configuration Options](https://image.slidesharecdn.com/hunt-replicationandreplicasets-130625160506-phpapp01/85/Basic-Replication-in-MongoDB-13-320.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}
]
}
> rs.initiate(conf)
Configuration Options
Primary DC](https://image.slidesharecdn.com/hunt-replicationandreplicasets-130625160506-phpapp01/85/Basic-Replication-in-MongoDB-14-320.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}
]
}
> rs.initiate(conf)
Configuration Options
Secondary DC
Default Priority = 1](https://image.slidesharecdn.com/hunt-replicationandreplicasets-130625160506-phpapp01/85/Basic-Replication-in-MongoDB-15-320.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}
]
}
> rs.initiate(conf)
Configuration Options
Analytics
node](https://image.slidesharecdn.com/hunt-replicationandreplicasets-130625160506-phpapp01/85/Basic-Replication-in-MongoDB-16-320.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}
]
}
> rs.initiate(conf)
Configuration Options
Backup node](https://image.slidesharecdn.com/hunt-replicationandreplicasets-130625160506-phpapp01/85/Basic-Replication-in-MongoDB-17-320.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 : "someDCs"})
Tagging Example](https://image.slidesharecdn.com/hunt-replicationandreplicasets-130625160506-phpapp01/85/Basic-Replication-in-MongoDB-27-320.jpg)
Basic Replication in MongoDB
- 1. Internal Tools, 10gen J. Randall Hunt #MongoDBDays Introduction to Replication and Replica Sets
- 2. Agenda • Replica Sets Lifecycle • Developing with Replica Sets • Operational Considerations
- 3. Why Replication? • How many have faced node failures? • How many have been woken up from sleep to do a fail-over(s)? • How many have experienced issues due to network latency? • Different uses for data – Normal processing – Simple analytics
- 5. Replica Set – Creation
- 6. Replica Set – Initialize
- 7. Replica Set – Failure
- 8. Replica Set – Failover
- 9. Replica Set – Recovery
- 10. Replica Set – Recovered
- 11. Replica Set Roles & Configuration
- 13. > 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) Configuration Options
- 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) Configuration Options Primary DC
- 15. > 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) Configuration Options Secondary DC Default Priority = 1
- 16. > 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) Configuration Options Analytics node
- 17. > 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) Configuration Options Backup node
- 21. Write Concern • Network acknowledgement • Wait for error • Wait for journal sync • Wait for replication
- 22. Unacknowledged
- 23. MongoDB Acknowledged (wait for error)
- 24. Wait for Journal Sync
- 26. Tagging • Control where data is written to, and read from • Each member can have one or more tags – tags: {dc: "ny"} – tags: {dc: "ny", subnet: "192.168", rack: "row3rk7"} • Replica set defines rules for write concerns • Rules can change without changing app code
- 27. { _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 : "someDCs"}) Tagging Example
- 28. Wait for Replication (Tagging)
- 29. Read Preference Modes • 5 modes – primary (only) - Default – primaryPreferred – secondary – secondaryPreferred – Nearest When more than one node is possible, closest node is used for reads (all modes but primary)
- 31. Maintenance and Upgrade • No downtime • Rolling upgrade/maintenance – Start with Secondary – Primary last
- 32. Replica Set – 1 Data Center • Single datacenter • Single switch & power • Points of failure: – Power – Network – Data center – Two node failure • Automatic recovery of single node crash
- 33. Replica Set – 2 Data Centers • Multi data center • DR node for safety • Can’t do multi data center durable write safely since only 1 node in distant DC
- 34. Replica Set – 3 Data Centers • Three data centers • Can survive full data center loss • Can do w= { dc : 2 } to guarantee write in 2 data centers (with tags)
- 35. Recent improvements • Read preference support with sharding – Drivers too • Improved replication over WAN/high-latency networks • rs.syncFrom command • buildIndexes setting • replIndexPrefetch setting
- 36. Just Use It • Use replica sets • Easy to setup – Try on a single machine • Check doc page for RS tutorials – http://docs.mongodb.org/manual/replication/#tutorials
- 37. Internal Tools, 10gen J. Randall Hunt #MongoDBDays Thank You
- 40. Next Sessions at 12:40 5th Floor: West Side Ballroom 3&4: Indexing and Query Optimization West Side Ballroom 1&2: Text Search (Beta) Juilliard Complex: Business Track: Building a Personalized Mobile App Experience Using MongoDB atADP Lyceum Complex:Ask the Experts 7th Floor: Empire Complex: Scaling MongoDB; Sharding Into and Beyond the Multi-Terabyte Range SoHo Complex:Automated Slow QueryAnalysis: MongoDB & Hadoop, Sittin' in a Tree