This document discusses high availability techniques for MySQL databases. It defines high availability as having a high "availability" or uptime, measured by metrics like MTBF and MTTR. The document outlines several techniques to improve high availability, including increasing MTBF through monitoring, testing, and redundancy, and decreasing MTTR through failover capabilities and redundancy. It then discusses several high availability technologies for MySQL, including replication, SANs, DRBD, MySQL Cluster, Percona XtraDB Cluster, load balancing, and more. It concludes by saying recommendations are too complex for the slides and to examine suitable solutions based on needs.

1. MySQL High Availability
Baron Schwartz
February 2011

2. Agenda
● Defining High Availability
● High Availability Techniques
● High Availability Technologies
● Recommendations (?)

3. What is High Availability?
● What is Availability?
● How high is enough?
○ "I need six nines"
● MTTR and MTBF
● Service availability versus data availability

4. Achieving HA
● Increase MTBF
○ "Best practices" and proactive measures
○ Monitoring and alerting
○ Build systems that can soft-fail or run degraded
● Reduce MTTR
○ This is reactive, not proactive
○ Add redundancy to remove SPOFs
○ Add failover/takeover capabilities

5. Increasing MTBF
● Test regularly; find failures before they matter
● Least privilege
● Keep things neat, clean, systematic
● Manage changes carefully
○ More about this in "causes of downtime" talk
● Good system architecture & design
○ Loose coupling, degraded functionality, load shedding,
etc

6. Decreasing MTTR
● Two important components:
1. Notice problems quickly
2. Resolve them quickly
● Technical measures help with part 2
○ Systems that have no SPOF, etc
○ Redundancy and failover capability

7. Data Availability
● This is a related topic, but distinct from HA
● Typically want a strong D guarantee in ACID
● Usually implemented with synchronous replication
● In practice, usually inseparable from HA
● Makes HA much harder
○ It's easy to be HA if it's OK to lose your data!

8. Technologies
● Replication
● SAN
● DRBD
● MySQL Cluster (NDB)
● Percona XtraDB Cluster (Galera)
● Clustrix and similar
● Load Balancing and Proxies

9. Replication
● The classic approach, used for years by many
● Can have very short MTTR
● Essential problem: asynchronous
● Has a "glass ceiling"
● Some failover managers available, but most aren't great

10. SAN
● "Enterprise" approach
● Really a zero-data-loss technique, not HA
● MTTR can be (very) high
● SAN is still a SPOF (can be mitigated)

11. DRBD
● Replicated storage
● "Enterprise" zero-data-loss approach
● Relatively high MTTR
● DRBD + replication historically not a great approach
● There is Percona-PRM; worth knowing about

12. Percona XtraDB Cluster
● Built on modified InnoDB + Galera sync replication library
● Multi-master, synchronous, write-anywhere
● Beta; see percona.com/software/

13. Percona XtraDB Cluster
● Strengths?
○ Transparent, familiar technology*
○ Real HA and protection from data loss
○ No lagging replicas
○ Data stored redundantly; all nodes equal
● Weaknesses?
○ As slow as the slowest node
○ Data stored redundantly; probably limits total size
○ Deadlocks and rollbacks can increase
* Uses optimistic conflict resolution, not pessimistic

14. MySQL Cluster (NDB)
● Shared-nothing approach: true HA
● Not fully general-purpose, but good for lots of things
● Not "vanilla MySQL" - NDB is a separate database
● Improving rapidly; MySQL Cluster 7.2 GA today!
● Unbeatable for specific purposes

15. Clustrix et al.
● Clustrix
○ NDB-ish, but queries execute fully on the nodes
○ Validated extensively by Percona
● Xeround
○ Ditto; for the cloud; not evaluated by Percona yet
● Continuent Tungsten
○ Replacement for MySQL replication
○ Kind of an opensource GoldenGate

16. Load Balancing and Proxies
● Usually used in combination with replication
● Usually require some scripting/integration
● $YOUR_LOAD_BALANCER_HERE
● HAProxy, pen, etc
● MySQL Proxy
● ScaleBase, ScaleArc

17. Recommendations
● Sorry, too complex for these slides :)
● Usual approach:
○ Cross off unsuitable solutions
○ Examine what's left
● Anti-recommendations:
○ Be careful with replication-based HA
○ MMM can be troublesome in some configurations
○ MySQL Proxy doesn't really excel in most cases

18. Percona XtraDB Cluster
● Writes update all nodes
● Reads execute locally
Comparison of Clustering Methods

19. MySQL Cluster (NDB)
● Writes update all copies of data
● Reads execute locally + distributed
Comparison of Clustering Methods

20. Clustrix
● Writes update all copies of data
● Reads execute fully distributed
Comparison of Clustering Methods

21. What's Percona Been Up To?
http://tools.percona.com/

22. Resources
● Free webinars: www.percona.com/webinars
● White papers on preventing downtime:
○ www.percona.com/about-us/mysql-white-papers
○ "Causes of downtime" paper
○ "Preventing downtime" paper
● Slides from Percona Live DC 2012
○ Yves's talk on Percona-PRM and MySQL Cluster
○ percona.com/live/

23. Santa Clara, CA
April 10-13
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