MySQL - Scale Out @ CloudParty 2013 Milano Talent Garden

How to scale out MySQL databasesCloudParty 2013 – Database in Cloud – Milan 27 Sep

Walter Dal Mut - @walterdalmut

www.corley.it

http://www.corley.it/

http://www.slideshare.net/ziobrando/ddd-dirty-harry-styleCloudParty 2013 - 27 Sep Milan Italy

Why we are interested in:Scale-Out databases on the Cloud?

CloudParty 2013 - 27 Sep Milan Italy


We need more resources

Single hard drives has limitsNetwork interfaces too

And so on...


We are also looking for availability


we want toensure SERVICE availability

and NOTserver availability



Availability % Downtime per Month

90% 72 Hours

95% 36 Hours

99% 7.2 Hours

99.5% 3.6 Hours

99.8 86.23 Minutes

99.95 21.56 Minutes

99.99 4.32 Minutes

Ok, we can start...First of all we have to talk about

replication



How many kind of replications?


Synchronous Replication


Sync Replicais the process that writes data to the primary and secondary node at the

SAME time.It is more expensive and introduce latency that slow down the application

because.


Asynchronous Replication


Async ReplicaIs the process that writes data to the primary and secondary node at different

time.Is more simple, a primary node doesn't care about others


Semi-Synchronous Replication


Semi-Sync ReplicaOn the master side, write when at least one slave acknowledges that is has

received all events


Which kind of replications can we sort up with MySQL?


ASYNC Master/Slave Replica(Read Replicas)


ASYNC Master/Master Replica(Read/Write replicas)


Always Async!That means: LAG REPLICA TIME


Just this?


Semi-Sync ReplicasStarting with MySQL 5.5Implemented by plugins

http://dev.mysql.com/doc/refman/5.5/en/replication-semisync.html


A slave indicates that it is semy-sync capableOn the master side, write when at least one slave acknowledges that is has

received all eventsIf no one slave is available, the master revert to async replication

If one slave catches up, the master returns to semi-sync replication


And if I need something SYNC?


Percona XtraDB ClusterMySQL Cluster NDB (internally)


Instead using MySQL Replicationwe can look for replication of network devices

“Distributed Replication Block Device”DRBD

http://www.drbd.org/users-guide-8.3/ch-heartbeat.htmlhttp://dev.mysql.com/doc/refman/5.0/en/ha-drbd.html


http://www.drbd.org/users-guide-8.3/ch-heartbeat.html

http://dev.mysql.com/doc/refman/5.0/en/ha-drbd.html


DRBD is essentially a RAID 1 on a network


DRBD has 3 replication modes:A → Async

B → Semi Sync

C → Sync


global { usage-count no; }common { net { protocol C; } }resource r0 { on drbd01 { device /dev/drbd0; disk /dev/sdb1; address 192.168.0.1:7788; meta-disk internal; } on drbd02 { device /dev/drbd0; disk /dev/sdb1; address 192.168.0.2:7788; meta-disk internal; }}


Exactly like a RAID1 array you cannot query the “second device”

It means that: “the device” on a secondary node is not mounted/available



DRBD is a RAID on networksyour entire system doesn't switch automatically in case of

failures.In order to automate the failover switch you can use

Peacemaker/Corosync





AWS RDS – Multi AZ




Master/Slave – Read ReplicasAsync Replication




Master-Slave: Writes-Reads




Capacity left for READS

Capacity left for WRITES

Master-Slave: Write Intensive


Master/Master – Multi MasterAsync Replication


A primary nodesee the secondary node

as a slaveand vice-versa


Master M1 Slave M1


Master M1Slave M2

Slave M1Master M2


Super Easy! But, it works?


YES?


Why?


Because of auto increment columns


As a cause of LAG replication time two auto-increment keys conflicts quite immediately in a

production environment!


1 1

22

APPLICATION APPLICATIONMASTER 1 MASTER 2

INSERT

INSERT

Both replica stops immediately on replication (split brain)

INSERT INTO table (id) VALUES (2)

INSERT INTO table (id) VALUES (2)


Any solution?


Avoid auto-increments columns



Work on auto-increment columns


l auto_increment_increment controls the increment between successive AUTO_INCREMENT values.

l auto_increment_offset determines the starting point for AUTO_INCREMENT column values.


server-id=1auto-increment-offset = 1

auto-increment-increment = 4Produces: 1 5 9 13 17 21 25

server-id=2auto-increment-offset = 2

auto-increment-increment = 4Produces: 2 6 10 14 18 22 26



Collisions can occurs on all unique indexesUser names, emails e unique fields in general causes

collisions in a asynchronous replicated database.The application must ensure zero collisions


You have to deal also with inconsistencies


Master Master

Application

UPDATE users SET email='[email protected]' where id=1;

UPDATE users SET email='[email protected]' where id=1;

[email protected]

[email protected]

[email protected]

[email protected]


Do we have scale writes?


NO!


Master-Master: Writes-Reads

Every write still has to be performed on both masters!CloudParty 2013 - 27 Sep Milan Italy

We can use Master/Master for:

High Availability (Hot Stand-By)Maintenance Tasks


Thanks for listeningAny question?

[email protected]@walterdalmut


mailto:[email protected]

MySQL - Scale Out @ CloudParty 2013 Milano Talent Garden

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