Replication with MariaDB at SUSE Expert Day 2014 Warsaw

© MariaDB Corporation Ab05/10/2014 1

© MariaDB Corporation

Replication with MariaDBAchieving Scalability and High Availability using MariaDB,

Replication and MariaDB Galera Cluster

Anders Karlsson, Principal Sales Engineer

* *05/10/2014 2


Agenda

• About Anders Karlsson

• What is replication good for?

• How does MariaDB Replication work?

• MariaDB Replication enhancements

• Intro to MariaDB Galera Cluster

• Questions ? Answers?

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Who am Anders Karlsson?

• Principal Sales Engineer at MariaDB

• Former Database Architect at Recorded Future, Sales Engineer and Consultant with Oracle, Informix, TimesTen, MySQL / Sun / Oracle etc.

• I have been in the RDBMS business for some 30 years

• I have also worked as Tech Support engineer, Porting Engineer and in many other roles

• Outside SkySQL I build websites (www.papablues.com), develop Open Source software (MyQuery, mycleaner, OraMySQL etc), am a keen photographer, has an affection for English Real Ales and a great interest in computer history

• I am a proud father of two gorgeous and smart twins

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So, what is MariaDB replication used for?

• High Availability

• Scale-out

• Backup servers

• Disaster Recovery

• Reporting servers

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Replication for High-Availability

• MariaDB Replication is asynchronous, which is an issue for HA in this case

• Failover Slave has to wait for Slave to catch up

• Using MHA makes the process somewhat automatic and less problematic

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Replication for Scale-out

• Scale-out is exactly what MariaDB Replication was intended to do from the start

• Use as a Write-only master and one or more Read-only slaves

• Slaves has low load on the Master

• Easy to use and set up

• Often combined with a Load Balancer

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Load Balancer


Replication for Backup servers

• Oldschool means cold disk backups, online backups or mysqldump backups at regular intervals

• These days, backups are done on asynchreplicas, sometimes combines with the backup methods above (i.e. cold slave backup)

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Replication for Disaster Recovery

• Async replication is great for replication between Data Centers

• Disaster Recovery usually has less stringent requirements that, say, Backup replication. A DR site should have to use used more than very seldom

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Data Center Disaster Recovery Site


Replication for Reports

• Using Replication for Report servers is slightly different

• Report servers may have a slightly different schema / indexing and is probably differently tuned

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So, how does MariaDB Replication work?

• The replication is Asynchronous, or rather, data is pulled by the Slave from the Master as fast as possible

• To know what to replicate to the slave, the Master keeps an ordered log, the bin-log, of statements to replicate

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• The Slave keeps track of the position in the Master bin-log either by a file/position pair of by a global transaction id

• The Slave reads the Master bin-log and replicates this to a Relay-log on the slave of statements to be replicated

• This is the Slave IO-thread

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• Then the Slave reads the Relay-log and applies the statements to the Slave database

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Master SlaveBin log Relay log


Simple and effective, right? Well...

• There are a few things to note

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There is nothing special with a Slave!

• Yes, this is true, and this is different from some other replication systems

• A slave runs the exact same software as the master

• The only difference is how the Master and Slave are configured!

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A Slave can be a Master also!

• This is sometimes useful when you have Many Slaves on a master

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Master Intermediate

Master

Bin log Relay log Bin log Relay log Slave


Replication can be statement based or row based

• Statement based means that the SQL text of the statement is replicated• UPDATE orders SET customer_id = 57 WHERE

order_id = 19

• Row based means that each row change is replicated as a binary entity which is idempotent

• There is also a MIXED format, which is a mix of the two above

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Replication can optionally be semi-synchronous

• Semi-sync is an option to MariaDB Replication

• Semi-sync means that the master will ensure that a committed transaction is replicated to at least N slaves before being accepted

• If there is a failure in replication, then the Master can fall back to normal Asynchronous replication

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Replication just replicates! (Surprise!)

• What this means is that there is nothing in the replication system that guarantee that the Slave and the Master are identical, beyond replication DML

• If you send DML directly to a Slave, then the effect of any upcoming replication data might be different than on the master or might fail

• But if you know what you are doing, this is quite alright!

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A slave might be a master to the Master

• Two or more masters can be in a ring in a Multi-Master setup

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Master Bin logRelay log Relay log Master Bin log


Without Semi-sync replication, the Master doesn’t care about the Slaves

• The Master just writes to the Bin-log, nothing else

• The Master also purges the bin-logs as needed

• There is no real “cluster” setup where the nodes know about each other and act in a particular manner

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MariaDB 10 – One Slave / Many Masters

• As the Master only has to manage the Bin-Log, you can have more than one Slave on one Master

• Before MariaDB 10, a Slave could only be a Slave of one Master

• With MariaDB 10, a Slave can replicate from more than 1 Master

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One Slave for Many Master

• A Data Warehouse that gets data from multiple sources

2306/10/2014

ERP System CRM System Data Warehouse


The serialized Binlog – Slave lag

• The Binlog logs operations from multiple threads in order in one log

• This means that the log has to be applied serialized also

• This in turn means that the SQL thread is single threaded

• And this means that the Slave is slower than the Master, which means Slave lag

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The serialized Binlog – The fix

• MariaDB 10 has multiple parallel Slave threads

• This is based on the Binlog Group commit functionality

• Application by application parallelism is also available

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MariaDB Galera Cluster – HA Replication

• For true High Availability, we want all servers in a consistent state

• This requires Synchronous replication

• But HA also requires

• Controlled Failover

• Cluster status information and management

• Add and Remove cluster nodes

• To the rescure: MariaDB Galera Cluster

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MariaDB Galera Cluster in short

• MariaDB Galera Cluster is separate from and does not depend on MariaDB Replication

• MariaDB Galera Cluster is a complete HA Cluster setup

• Based on and requires InnoDB

• Synchronous replication

• Multi-master with conflict detection

• All nodes are “Cluster aware”

• Add and Remove node is built-in

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MariaDB Galera Cluster setup

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WSREP

Library

WSREP

Library

• MariaDB 10.0 version includes WSREP API

• MariaDB 10.1 has this as standard, for 5.5 and 10.0 patched versions are available

• WSREP API installed as a MariaDB Plugin

• WSREP does replication, failover and management


MariaDB Enterprise

• MariaDB Enterprise is the MariaDB Subscription offered by MariaDB

• Includes monitoring and management software

• Includes world-class support

• Includes Certified Binaries

• And much more!

• MariaDB Enterprise Cluster is MariaDB Enterprise for MariaDB Galera Cluster

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Questions? Answers?

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The question is not “What is

the answer?”, the question is

“What is the question?”.

Henri Poincaré

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Replication with MariaDB at SUSE Expert Day 2014 Warsaw

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