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MongoDB Replication
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Sridhar Nanjundeswaran
September 14, 2012
Programming
1
120
MongoDB Replication
Presented at MongoDB Seattle Sept 2012.
Sridhar Nanjundeswaran
September 14, 2012
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Transcript
1 Sridhar Nanjundeswaran, 10gen
[email protected]
@snanjund
2 • Introduction to Replica Sets • Developing with Replica
Sets • Operational Considerations • Miscellaneous
Introduction to Replica Sets What is it? Configuration Options
4 Node 1 Node 2 Node 3
5 Node 1 Secondary Node 2 Secondary Node 3 Primary
Replication Replication Heartbeat
6 Node 1 Secondary Node 2 Secondary Node 3 Primary
Heartbeat Primary Election
7 Node 1 Secondary Node 2 Primary Node 3 Primary
Heartbeat Replication
8 Node 1 Secondary Node 2 Primary Node 3 Secondary
Replication Heartbeat Replication
9 • Priorities – Help control election – Secondary only
• Slave Delay – Purposely delay replication • Hidden – Not seen as part client connection • Tagging
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 { _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"})
Developing with Replica Sets Consistency Write Preference Read Preference
13 Primary Secondary Secondary Read Write Driver Client
14 Primary Read Write Driver Read Secondary Secondary Client Application
15 • Fire and forget • Wait for error •
Wait for journal sync • Wait for replication
16 Driver Primary write apply in memory
17 Driver Primary getLastError apply in memory
18 Driver Primary getLastError apply in memory write j:true Write
to journal
19 Driver Primary getLastError apply in memory write w:2 Secondary
replicate
20 • 5 modes – primary (only) - Default –
primaryPreferred – secondary – secondaryPreferred – nearest
21 • Custom read preferences • Control where you read
from – E.g. { "disk": "ssd", "use": "reporting" } • Use in conjunction with standard read preferences – Except primary
Operational Considerations Upgrade/Maintenance Common Deployment Scenarios
23 • No downtime • Rolling upgrade/maintenance – Start with
Secondary – Primary last
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 • 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 • 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
Miscellaneous Behind the scenes What’s new in 2.2
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 • Full read preference support in mongos – Drivers
too • Improved RS lag logging • rs.syncFrom command • buildIndexes setting • replIndexPrefetch setting
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 @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 !
[email protected]
@snanjund