The document discusses various high availability solutions for MySQL databases, including: 1) MySQL replication which allows for scaling out reads across slave servers but has a single point of failure at the master. 2) Master-master replication which removes the single master point of failure but makes the system more complex and can lead to data inconsistencies. 3) Solutions using shared storage like SANs or DRBD to synchronize data between active-passive nodes for failover, avoiding data inconsistencies but having higher costs and complexity. 4) Synchronous replication options like Galera and MySQL Cluster that allow for active-active usage with no data lag but have their own performance impacts and complexity tradeoffs.

1. Various MySQL
High Availability (HA) Solutions
Percona Live MySQL Conference,
London, Oct 24th and 25th, 2011
Oli Sennhauser
Senior MySQL Consultant at FromDual GmbH
oli.sennhauser@fromdual.com
www.fromdual.com 1

2. About FromDual GmbH (LLC)
● FromDual provides neutral and independent:
● Consulting for MySQL (on-site and remote)
● Remote-DBA Services / MySQL Operations
● Premium Support (ex. MySQL Basic and Silver)
● Training for MySQL
● Consulting partner of the Open Database Alliance
(ODBA.org)
● Oracle Silver Partner (OPN)
● More information you can find at:
http://www.fromdual.com
www.fromdual.com 2

3. Contents
Various MySQL High Availability (HA) Solu-
tions
➢
MySQL Replication / MySQL Scale-Out
➢
High-Availability with Replication
➢
Master-Master Replication
➢
Active/passive fail-over with SAN
➢
Active/passive fail-over with DRBD
➢
Galera (synchronous) Replication
➢
MySQL Cluster
➢
Tungsten Replicator
www.fromdual.com 3

4. MySQL Scale-Out vs Scale-Up
● Costs
Scale-Up
● MySQL Design
● Physical bottlenecks
● „Relaxation of Constraints“
Scale-Out
www.fromdual.com 4

5. High-Availability with Replication
Application
read only
VIP rtw
Slave Reporting
Slave M Master
async!
Slave Backup
Slave 1 Slave 2 Slave 3
...
Load balancer
● Fail-over?
www.fromdual.com 5

6. Replication fail-over
Application
read only
VIP rtw
Slave Reporting
Slave M Master
async!
Slave Backup
Slave 1 Slave 2 Slave 3
...
Load balancer
www.fromdual.com 6

7. Advantages / Disadvantages
Simple „standard“ Set-up
Master is a SpoF! (Single Point of Failure)
If master fails → which Slave becomes new master?
Switch → a lot of work, delicate!
There are tools to help (MMM v1/v2, MHA, Tungsten, ...)
Fail-over Site is already warm/hot!
Works very well if r >> w
Data inconsistencies (mk-table-check/sync)
Delay Master/Slave
Slave lagging (Slave as bottleneck)
www.fromdual.com 7

8. Master-Master Replikation
App App App
VIP
M1 M2
Slave1 Slave2 Slave3 SlaveBackup
Load balancer (LB)
www.fromdual.com 8

9. Master-Master Replication
App App App
VIP
M1 M2
Slave1 Slave2 Slave3 SlaveBackup
Load balancer (LB)
www.fromdual.com 9

10. Advantages / Disadvantages
Only slightly more complex than Master/Slave
Careful when writing on both Masters!
For a “balanced” system at least 2 Slaves are needed
You will NOT get more I/O throughput!
Data in-consitency possible because of asynchronous replication
Fail-over Site is already warm/hot!
Works very well if r >> w
Data inconsistencies (mk-table-check/sync)
If Master fails, half of the Slave are out of sync!
A little more complicated to (re-)set-up
Delay Master/Slave
Slave lagging (Slave as bottleneck)
www.fromdual.com 10

11. Active/passive fail-over with SAN
App App App
VIP
M' M
SAN
Slave1 Slave2 Slave3
Load balancing (LB)
www.fromdual.com 11

12. Active/passive fail-over with SAN
● SPOF! App App App
VIP
M' M
!!! SAN
Slave1 Slave2 Slave3
Load balancing (LB)
www.fromdual.com 12

13. Advantages / Disadvantages
Synchronous replication
● I/O throughput depends on SAN (I/O system)
No data IN-consistencies possible
SAN is a SpoF!
Expensive if SAN is not available yet.
SAN's are not easy to handle!
Fail-over Site is still cold!
Half of the hardware is idling
Only one possible Data source
Slaves are automatically and properly fail-overed
Far more complex to set-up
www.fromdual.com 13

14. Active/passive fail-over with
DRBD
App App App
VIP
M' M
“Poor man's SAN” DRBD
Slave1 Slave2 Slave3
Load balancing (LB)
www.fromdual.com 14

15. Active/passive fail-over with
DRBD
App App App
VIP
M' M
DRBD
Slave1 Slave2 Slave3
Load balancing (LB)
www.fromdual.com 15

16. Advantages / Disadvantages
Synchronous replication
No data IN-consistencies possible
I/O throughput lower
Slaves are automatically and properly fail-
overed
Fail-over Site is still cold!
Half of the hardware is idling
Only one possible Data source
Far more complex to set-up
www.fromdual.com 16

17. Galera (synchronous) Replication
App App App
Load balancing (LB)
Node 1 Node 2 Node 3
wsrep wsrep wsrep
Galera replication
www.fromdual.com 17

18. Galera (synchronous) Replication
App App App
Load balancing (LB)
Node 1 Node 2 Node 3
wsrep wsrep wsrep
Galera replication
www.fromdual.com 18

19. Advantages / Disadvantages
Synchronous replication
Based on InnoDB SE (other SE theoretically possible)
Active-active real multi-master topology
Read and write to any cluster node
Automatic membership control
True parallel replication, on row level
No slave lag
No lost transactions
Read AND write scalability (Read Scale-Out!)
Patch off MySQL binaries (Codership provides binaries)
Be aware of Hot Spots on rows
Higher probability of dead locks
Full sync blocks for writing → 3 nodes
Initial sync for very big databases (>>50 Gbyte) with mysqldump
www.fromdual.com 19

20. MySQL Cluster
App App App
Load balancing (LB)
SQL nodes MySQL MySQL MySQL
Server Server Server
MGM client MGM client
NDB Cluster
(Data nodes)
ndbd ndbd
mgmd mgmd
ndbd ndbd
Data nodes / Mgmt nodes
www.fromdual.com 20

21. Advantages / Disadvantages
Synchronous replication
No data IN-consistencies possible
Extremely high throughput (if done correctly)
Good for read AND write
New beast to tame (MySQL Cluster != MySQL!)
More complex to set-up and operate than normal MySQL
Not for disaster fail-over (<= 7.1)
Bad for complex queries (Joins, <= 7.1)
At least 3 machines (better 4) are need.
High demand on RAM and Network
Only one possible Data source
www.fromdual.com 21

22. Tungsten Replicator
www.fromdual.com 22

23. Advantages / Disadvantages
● Similar to MySQL Replication
Introduces Global Transaction-ID
Asynchronous Replication
Bases on MySQL Binary Log
For: MySQL, PostgreSQL, Oracle and Drizzle
Requires Java and Ruby?
Multi Source Replication
Failover should be easier to handle
www.fromdual.com 23

24. Questions ?
Discussion ?
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