This document discusses various high availability solutions for MySQL databases. It begins with an overview of high availability concepts and considerations. It then covers MySQL replication, disk replication using DRBD, MySQL Cluster, and other tools like Pacemaker, Galera replication, MMM, Tungsten Replicator, Red Hat Cluster Suite, Solaris Cluster, and Flipper. The document provides details on how each solution works and its advantages and disadvantages for providing redundancy and high availability for MySQL databases.

1. MySQL High Availability Solutions
Lenz Grimmer <lenz@grimmer.com>
<
http://lenzg.net/ | Twitter: @lenzgr
2011-01-26 | San Francisco MySQL Meetup | USA

2. $ whoami
1998 2002
2008 2010

3. Agenda
● High Availability: Concepts &
Considerations
● MySQL Replication
● DRBD / Pacemaker
● MySQL Cluster
● Other HA tools/applications

4. Single MySQL Server
MySQL Client
SQL (SELECT, INSERT,
UPDATE, DELETE)
MySQL Storage Engines
(InnoDB, MyISAM, PBXT...)
Disk Storage
(XFS, ReiserFS, JFS, ext3...)

5. Why HA?
● Something can and will fail
● Service Maintenance
● Downtime is expensive
● Adding HA to an existing system is complex

6. Elimination of the SPOF
● Identify what will fail eventually
● Hard disks
● Fans
● Consider what might fail
● Application crashes
● OOM-Situations, Kernel-Panics
● Network connections, Cables
● Power supply

7. What is HA Clustering?
● Redundancy
● One system or service goes down → others
take over
● IP address takeover, service takeover
● Ensuring data availability & integrity
● Not designed for high-performance

8. High Availability Levels

9. Rules of High Availability
● Prepare for failure
● Aim to ensure that no important data is
lost
● Keep it simple, stupid (KISS)
● Complexity is the enemy of reliability
● Automate it
● Test your setup frequently!

10. HA Components
● Heartbeat
● Checks that services that are monitored, are alive.
● Can check individual servers, software services,
networking etc.
● HA Monitor
● Configuration of the services
● Ensures proper shutdown and startup
● Allows manual control
● Shared storage / Replication

11. Split-Brain
● Communications failures can lead to
separated partitions of the cluster
● If those partitions each try and take control
of the cluster, then it's called a split-brain
condition
● If this happens, then bad things will happen
● Use Fencing or Moderation/Arbitration to
avoid it

12. Redundancy Using MySQL Replication
MySQL Replication

13. MySQL Replication
● Unidirectional
● Statement- or row-based (MySQL 5.1)
● Built into MySQL
● Easy to use and set up
● One Master, many Slaves
● Asynchronous – Slaves can lag behind
● New in MySQL 5.5: Semisync Replication

14. MySQL Replication (2)
● Master maintains Binary logs & index
● Replication on Slave is single-threaded
http://forge.mysql.com/wiki/ReplicationFeatures/ParallelSlave
● No automated fail-over
● No heartbeat, no monitoring
● New in 5.5: replication heartbeat

15. MySQL Replication - Overview
Read & Write
Web/App
Server
Write
Relay
Log
mysqld SQL
I/O
Threa
Thread
d
Index &
Binlogs
Data
Replication Binlog Data
mysqld
MySQL Master MySQL Slave

16. Statement-based Replication
● Pro
✔ Proven (around since MySQL 3.23)
✔ Smaller log files
✔ Auditing of actual SQL statements
✔ No primary key requirement for replicated tables
● Con
✗ Non-deterministic functions and UDFs
✗ LOAD_FILE(), UUID(), CURRENT_USER(),
FOUND_ROWS()
(but RAND() and NOW() work)

17. Row-based Replication
● Pro
✔ All changes can be replicated
✔ Similar technology used by other RDBMSes
✔ Fewer locks required for some INSERT, UPDATE or
DELETE statements
● Con
✗ More data to be logged
✗ Log file size increases (backup/restore implications)
✗ Replicated tables require explicit primary keys
✗ Possible different result sets on bulk INSERTs

18. Replication Topologies
Master > Slave Master > Slaves
Master > Slave > Slaves Masters > Slave (Multi-Source)
Ring (Multi-Master)
Master < > Master (Multi-Master)

19. Master-Master Replication
● Two nodes are both master and slave to
each other
● Useful for easier failover
● Not suitable for (write) load-balancing
● Don't write to both masters
simultaneously!
● Use Sharding or Partitioning instead
(e.g. MySQL Proxy)

20. MySQL Replication as a HA Solution
● What happens if the Master fails?
● What happens if the Slave fails?
● This doesn’t sound like High Availability!
● Yes!
● Replication is only part of a HA
configuration

21. Pacemaker (Linux-HA)
● Supports 2 or more Nodes (v2)
● Resource monitoring (Apps and HW)
● Active fencing mechanism (STONITH)
● Node failure detection in seconds
● Supports many applications (incl. MySQL)
● http://clusterlabs.org/
● http://www.clusterlabs.org/wiki/Load_Balanced_MySQL_Replicated_Cluster
● http://www.clusterlabs.org/wiki/DRBD_MySQL_HowTo

22. Replication & HA
● Combined with Pacemaker
● Virtual IP takeover
● Slave gets promoted to Master
● Side benefits: load balancing & backup
● Can be tricky to fail back
● No automatic conflict resolution
● Proper failover needs to be scripted

23. Redundancy With Disk Replication
Disk Replication

24. DRBD
● Distributed Replicated Block Device
● “RAID-1 over network”
● Synchronous/asynchronous block replication
● Automatic resynchronisation
● Application-agnostic
● Can mask local I/O-Errors
● Active/passive configuration
● Dual-primary mode (requires cluster file sytem
like GFS or OCFS2)
● http://drbd.org/

25. DRBD in Detail
● DRBD replicates data blocks between to
block devices
● DRBD can be combined with Linux-HA and
other HA solutions
● MySQL runs normally Applications
on primary node
● MySQL is not active on Active Node Virtual IP Passive Node
the secondary node
● DRBD is Linux only DRBD

26. Redundancy Using Shared Storage

27. Replication vs. SAN
● Data Consistency / Integrity
● Synchronous vs. asynchronous
● SAN can become the SPOF
● Cold caches
● “Split brain”-Situations
● SAN/NAS I/O Overhead

28. Redundancy with MySQL Cluster

29. MySQL Cluster
● “Shared-nothing”-Architecture
● Automatic partitioning
● Distributed fragments
● Synchronous replication
● Fast, automatic fail-over of data nodes
● Automatic resynchronisation
● Transparent to MySQL applicationen
● Supports transactions
● http://mysql.com/products/database/cluster/

30. MySQL Cluster
● In-memory indexes
● Not suitable for all query patterns
(cross-table JOINs, range scans)
● No support for foreign keys
● Not suitable for long running transactions
● Network latency crucial
● Can be combined with MySQL replication
(RBR)

32. MySQL Cluster & Replikation
● MySQL Cluster
● Easy failover from one MySQL node to another
● Scaling write load using multiple SQL nodes
● Asynchronous replication from Cluster to
regular MySQL slaves
● Slaves take read load (InnoDB/MyISAM)
● Quick setup of new slaves (Cluster Online
Backup)
● Easy failover and fast recovery

33. http://johanandersson.blogspot.com/2009/05/ha-mysql-write-scaling-using-cluster-to.html

34. Galera Replication
● Patch for InnoDB plus external library
● Synchronous replication
● Single- or multi-master
● Multicast-Replication
● HA plus load sharing possible
● Certifikate-based replikation
(instead of 2PC)
● http://codership.com/products/mysql_galera

35. MMM
● MySQL Master-Master Replication
Manager
● Perl-Script for monitoring, failover and
management
● Master-master replication configuration
(one active writable master)
● Failover by moving virtual IP-Address
● Also supports read balancing
● http://mysql-mmm.org/

36. Continuent Tungsten Replicator
● Database-external solution
● Asynchronous, Master-Slave, Fan-out &
Fan-in
● Java
● Log-based
● Events are stored in the Transaction History
Log (THL)
● Modular architekture (Pipelines, Stages)
● http://continuent.com/community/tungsten-replicator

37. Red Hat Cluster Suite
● HA and load balancing
● Supports up to 16 nodes
● Shared storage
● Monitors services, file systems and network
status
● Fencing (STONITH) or distributed lock
manager
● Configuration synchronization
● http://www.redhat.com/cluster_suite/

38. Solaris Cluster / OpenHA Cluster
● Provides failover and scalability services
● Solaris / OpenSolaris (Project Colorado)
● Kernel-level components plus userland
● Agents monitor applications
● Geo Edition to provide Disaster Recovery
using Replication
● Open Source since June 2007
● http://hub.opensolaris.org/bin/view/Community+Group+ha-clusters/WebHome
● http://hub.opensolaris.org/bin/view/Project+ha-mysql/WebHome

39. Flipper
● Perl Script managing pairs of MySQL
servers replicating to each other.
● Automatic switchover, triggered manually
● Enables one half of the pair to be taken
offline for maintenance work while other
half carries on
● Moves IP addresses based on a role ("read-
only", "writable")
● http://provenscaling.com/software/flipper/

40. Q&A
Questions, Comments?

41. Thank you!
Lenz Grimmer <lenz@grimmer.com>
Twitter: @lenzgr
http://lenzg.net/