MongoDB Replica Sets

Replica Sets (MongoDB v1.6) Dwight Merriman (@dmerr) 10gen dmerr.tumblr.com

Basics
MongoDB replication is a bit like MySQL replication
Asynchronous master/slave at its core
Variations:
Master / slave
Replica Pairs (deprecated – use replica sets)
Replica Sets (today’s topic)

Replica Sets
A cluster of N servers
Any (one) node can be primary
Consensus election of primary
Automatic failover
Automatic recovery
All writes to primary
Reads can be to primary (default) or a secondary
v1.6

With Sharding

Replica Sets – Design Concepts
A write is only truly committed once it has replicated to a majority of servers in the set.
Thus, for important writes, the developer waits for confirmation of the cluster-wide commit with the getLastError command.
Writes which are committed at the master of the set may be visible before the true cluster-wide commit has occurred. This property, which is more relaxed than some traditional products, makes theoretically achievable performance and availability higher.
On a failover, if there is data which has not replicated form the primary, the data is dropped (see #1).

A Set Member 1 Member 2 Member 3

A Set Member 1 Member 2 PRIMARY Member 3

A Set Member 1 Member 2 DOWN Member 3 PRIMARY negotiate new master

A Set Member 1 Member 2 DOWN Member 3 PRIMARY

A Set Member 1 Member 2 RECOVER-ING Member 3 PRIMARY

A Set Member 1 Member 2 Member 3 PRIMARY

Configuration
{
_id : <setname>,
members: [
{
_id : <ordinal>,
host : <hostname[:port]>,
[, priority: <priority>]
[, arbiterOnly : true]
[, votes : n]
[, slaveDelay : s] [, hidden : true ]
}
, ...
],
settings: {
[getLastErrorDefaults: <lasterrdefaults>]
[, heartbeatSleep : <seconds>]
[, heartbeatTimeout : <seconds>]
[, heartbeatConnRetries : <n>]
}
}

Initiation
> cfg = {
... _id : "acme_a",
... members : [
... { _id : 0, host : "sf1.acme.com" },
... { _id : 1, host : "sf2.acme.com" },
... { _id : 2, host : "sf3.acme.com" } ] }
> use admin
> db.runCommand({replSetInitiate:cfg})

Set Member Types
Normal (priority == 1)
Passive (priority == 0)
DR (priority < 1.0) (coming soon)
Arbiter (no data, but can vote)

Commands
{ isMaster : 1 }
{ replSetGetStatus : 1 }
{ replSetInitiate : <config> }
{ replSetStepDown : true }
{ replSetReconfig : <config> }
> rs.help()

Questions?
Contact 10gen for on-site advisory sessions on MongoDB architecture, schema design, performance tuning, training…
[email_address]
irc://irc.freenode.net/#mongodb
http://groups.google.com/group/mongodb-user

http://d.hatena.ne.jp	2140
http://webcache.googleusercontent.com	17
http://paper.li	4
http://translate.googleusercontent.com	2
http://blog.sahsu.mobi	2
http://twitter.com	1

MongoDB Replica Sets

by Dwight Merriman on Aug 19, 2010

Accessibility

Categories

Tags

Upload Details

Usage Rights

6 Embeds 2,166

Statistics

MongoDB Replica Sets — Presentation Transcript