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High Availability with Galera Cluster by Seppo Jaakkola, Codership at the SkySQL Road Show 2013 in Berlin 18.6.2013
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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 :-)
