High Availability with Galera Cluster - SkySQL Road Show 2013 in Berlin

G a l e r a C l u s t e r

Seppo JaakolaCodership

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Agenda

● The Meaning of Galera● Galera Cluster Short Introduction● Migrating to Galera Cluster● Galera Project

● MariaDB Galera Cluster 5.5.29 GA

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What is the Meaning of Galera ?

Turns out it has different semantics in:● Italy● Uruguay● Brazil● Spain, Portugal, Russia...

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Galera in Italy

Che cosa significa la parola galera?

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Galera in Italy

Che cosa significa la parola galera?

Jail / Prison

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Galera in Italy

Che cosa significa la parola galera?

PoliziottoJail / Prison

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Otto Poliziotto ?

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Galera in Uruguay

Que significa galera en Uruguai?

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Galera in Uruguay

Que significaca galera en Uruguai?

Traditional tall hat

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Galera in Brazil

Como sobre em Brazil?

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Galera in Brazil

A Group of Happy People

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Galera in Spain, Portugal, Russia...

Here's the correct meaning for Galera...

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Galera in Spain, Portugal, Russia...

Galley

Galera Cluster

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MariaDB

Multi-Master Replication

Galera Replication

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MariaDB MariaDB

Multi-Master Replication

Galera Replication

There can be several nodes

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MariaDB MariaDB MariaDB

Multi-Master Replication

Galera Replication

There can be several nodes

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MariaDB MariaDB MariaDB

Multi-Master Replication

Galera Replication

Client can connect to any node

There can be several nodes

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MariaDB MariaDB MariaDB

Multi-Master Replication

Galera Replication

Client can connect to any node

There can be several nodes

read & write read & write read & write Read & write access to any node

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MariaDB MariaDB MariaDB

Multi-Master Replication

Galera ReplicationReplication is synchronous

read & write read & write read & write

Client can connect to any node

There can be several nodes

Read & write access to any node

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MariaDB

Multi-Master Replication

a

Multi-master cluster looks like one big database with multiple entry points

read & write read & write read & write

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MariaDB MariaDB MariaDB

Synchronous Replication

aGalera Replication

Read & write

Transaction is processed locally up to commit time

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MariaDB MariaDB MariaDB

Synchronous Replication

Galera Replication

commit

Transaction's write set is replicated to whole cluster

Slave queueSlave queue

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Galera Replication

MariaDB MariaDB MariaDB

Synchronous Replication

OK

Client gets OK status

Slave queueSlave queue

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Galera Replication

MariaDB MariaDB MariaDB

Synchronous Replication

Transaction is applied in slaves

Slave queueSlave queue

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MariaDB MariaDB MariaDB

How node failures are handled

a

Galera Replication

Load Balancing

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MariaDB MariaDB MariaDB

Quorum

a

Galera Replication

Load Balancing

● Galera uses quorum based failure handling:

– When cluster partitioning is detected, the majority partition "has quorum" and can continue

– A minority partition cannot commit transactions, but will attempt to re-connect to primary partition

– Note: 50% is not majority!=> Minimum 3 nodes recommended.

● Load balancer will notice errors & remove node from pool

Optimistic Concurrency Control

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Galera ReplicationA

Optimistic Concurrency Control

commit

Trx A

B

commit

Trx B

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Galera ReplicationA

Optimistic Concurrency Control

commit

Trx A

B

commit

Trx B

DEADLOCK eror

ROLLBACK

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Optimistic Concurrency Control

● Transactions process independently in each cluster node

● Transaction write sets will be replicated at commit time (before commit)

● Cluster wide conflicts will be resolved and conflict victim must rollback

Optimistic Concurrency Control

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Multi-Master or Not

● If your application can handle deadlock errors, multi-master is good to use

● However, if database has hot-spots, i.e. multi-master conflicts happen frequently, write performance will suffer

● But read scalability is always guaranteed ● Use Master-Slave, if deadlock errors are a

problem or conflict rate hurts your performance

Parallel Replication

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MariaDB

Parallel Replication

Slave queue

Slave thd Slave thdAny number of slave applier threads can be started

Slave control

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MariaDB

Parallel Replication

Slave queue

Slave thd Slave thdAny number of slave applier threads can be started

Slave control assigns write sets for slave appliers

Slave control

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MariaDB

Parallel Replication

Slave queue

Slave thd Slave thdAny number of slave applier threads can be started

Slave control assigns write sets for slave appliers

Slave control is on ROW levelSlave control

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MariaDB

Parallel Replication

Slave queue

Slave thd Slave thd

Slave control

Any number of slave applier threads can be started

Slave control assigns write sets for slave appliers

Slave control is on ROW level

Only applying is parallel commit order is dictated

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Parallel Applying

● Aka parallel replication● Every application will benefit of it, because it

works:● not on database● not on table● but on row level

● wsrep_slave_threads=n● How many slaves makes sense:

● Monitor wsrep_cert_deps_distance● Max ~4 * #CPUcores

Galera Cluster Benefits

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Galera Cluster

➢ Good Performance➢ Optimistic concurrency control➢ Virtually synchronous replication➢ Parallel Replication➢ Optimized Group Communication

➢ 99.99% transparent➢ InnoDB look & feel

➢ Automatic node joining➢ Works in LAN / WAN / Cloud

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Galera Cluster

➢ Synchronous multi-master cluster➢ no data loss➢ no slave lag➢ no slave failover

➢ For MySQL/MariaDB InnoDB➢ 3 or more nodes needed for HA➢ No single point of failure

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Synchronous Replication

That's more like it !!

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Synchronous Replication

That's more like it !!

Row based

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Synchronous Replication

That's more like it !!

Multi-Master

Row based

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Synchronous Replication

That's more like it !!

Multi-MasterAll have Oxford master degree

Row based

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Synchronous Replication

That's more like it !!

Multi-MasterAll have Oxford master degree

Synchronous

Row based

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Synchronous Replication

That's more like it !!

Top notch performance

Multi-MasterAll have Oxford master degree

Synchronous

Row based

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Synchronous Replication

That's more like it !!

Top notch performance

Multi-MasterAll have Oxford master degree

Arbitrator

Synchronous

Row based

Automatic Node Joining

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MySQL MySQL

Automatic Node Joining

Galera Replication

joiner

Cluster handshake

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MySQL Donor

Automatic Node Joining

Galera Replication

joiner

Send state

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MySQL MySQL

Automatic Node Joining

Galera Replication

joinerCatch up

Slave queue

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MySQL MySQL

Automatic Node Joining

Galera Replication

MySQL

Migrating to Galera Cluster

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Migrating to Galera Clustering

a

MySQLslave

MySQLmaster

MySQL master slave hierarchy

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MySQLslave

MySQLmaster

GaleraNode 1

Migrating to Galera Clustering

a

Install first Galera node to operate as MySQL slave

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MySQLslave

MySQLmaster

GaleraNode 1

Migrating to Galera Clustering

a

promote Galera node to operate as one node cluster

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MySQLslave

MySQLmaster

GaleraNode 1

Migrating to Galera Clustering

a

Join more nodes in Galera slave cluster

GaleraNode 2

GaleraNode 3

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MySQLslave

MySQLmaster

GaleraNode 1

Migrating to Galera Clustering

a

Move traffic to Galera cluster

GaleraNode 2

GaleraNode 3

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GaleraNode 1

Migrating to Galera Clustering

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Drop obsolete MySQL servers

GaleraNode 2

GaleraNode 3

Galera Project

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Galera Project

● Galera Cluster for MySQL● 5 years development● based on MySQL server community edition● Fully open source● Active community

● ~3 releases per year● Latest release 2.3● Major release 3.0 in the works

● MariaDB Galera Cluster 5.5.29 GA !!

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Who is using Galera?

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Galera Project

MySQL

MariaDBmerge

merge

MySQL Community Edition

MariaDBGalera Cluster for MySQL

MariaDB FeaturesAPI

MySQL

Galera Replication plugin

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Galera Project

API

Galera Replication plugin

API

MariaDB

MySQL Community Edition

MariaDB Galera Cluster

MySQL

Galera Cluster for MySQL

merge

Galera Replication plugin

MySQL

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Galera Support

CodershipLevel 3 support, Galera

MontyProgramLevel 3 Support, MariaDB

GaleraCluster

MariaDBGaleraCluster

SkySQLSupport Subscriptions

Questions?

Thank you for listening!Happy Clustering :-)