HIGH AVAILABILITY WITH
MYSQL
THAVA ALAGU
Staff Engineer, Database Group,
Sun Microsystems, Bangalore
thavamuni.alagu@sun.com
http://blogs.sun.com/thava/
Oct 2008

Welcome !
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LET US DISCUSS ABOUT …
 Aspects of High Availability
 MySQL Replication
 MySQL Cluster
 Application HA
 Resources
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ARCHITECTURE OVERVIEW
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HIGH AVAILABILITY
 Data Must Not be Lost
 Data + Application Must be
Available Always
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MYSQL SOLUTIONS …
 MySQL Replication (Asynchronous)
 MySQL Cluster (Synchronous)
 Supporting Solutions:
 MySQL Proxy (Alpha)
 MySQL Load Balancer (Based on Proxy)
 3rd Party Solutions from Partners and Others
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MYSQL REPLICATION HIGHLIGHTS
 Binary Log Updates From Master Applied at
Slave
 Usually One Master  Multiple Slaves
 Asynchronous Copy
 Slave could be used as Read-Only
 Geographically Distributed, Slow Links, OK
 Can be chained –
 Master  Slave/Master  Slave
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MYSQL REPLICATION BENEFITS
 Hot Standby Node for Fail-Over
 Can be Used for transparent Backups
 Load Balancing – Slaves Can be Active for Read
 Automated copy across geographically
distributed sites
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REPLICATION ARCHITECTURE
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REPLICATION TECHNIQUES AND
TIPS
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REPLICATION NOTES
 Binary logs rotated every 1GB
 You should clean/purge old logs
 Master/Slave similar architecture
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REPLICATION FORMATS
 3 Types:
 Statement Based Replication
 Row-based Replication
 Mixed Based Replication
 Depends on MySQL Version, Storage Engine
 Can override the defaults
 e.g. use row-format=row option
 Usually row based replication is safer
 But exceptions exist
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REPLICATION FOR BACKUPS
 Slave can be shutdown for Cold Backup
 Logical or File System backups
 Backup Logs too
 Logs can be used for Point-In-Time Recovery
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REPLICATE ACROSS STORAGE
ENGINES
 Slave can be ARCHIVE Engine
 Insurance against SE specific failures
 Faster Slave with No Transaction Engine
e.g. InnoDB to MyISAM
 How:
 Use storage_engine system variable
 Mysqldump; edit; reload
 Stop slave; Alter table …; Start Slave
 Disable some storage engines at Slave
 Create new tables with default engine
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REPLICATE FOR SCALING
 Use Multiple Slaves For Read Load
 Dedicate Master for Write Load
 Perfect for Load Balancing
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REPLICATE SELECTIVELY
 Filter at Slave – Database, Tables, specify in my.cnf
 replicate-wild-do-table=sales.%
 replicate-wild-do-table=finance.%
 Master Filters: binlog-do-db, binlog-ignore-db
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REPLICATE MULTILEVEL
 Less Load at Master
 Can Use Blackhole Engine for Master2
 Use log-slave-updates option at Master2
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MULTIMASTER (AVOID)
 2 Masters updating each other
 Ring of Masters
 Updates on disjoint sets
 Usually, Stay Away
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REPLICATION TOPOLOGIES
SUMMARY
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REPLICATE USING SSL
 For High Security
 Uses Certificate-Authority Certificate,
Server Public Key, Server Private Key
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REPLICATION SETUP UPGRADE
 Upgrade Slaves First, Then Master
 Shutdown, Upgrade, Restart
 Watch out Versions Upgradability
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REPLICATION COMMANDS
 On Master:
 Show master status
 Flush logs
 Show master logs
 Show binlog events
 Purge master logs to ‘mysql-bin.005’;
 On Slave:
 Change Master To master_host=‘hostA’ master_user=‘slave’
master_password=‘slavepassword’ ;
 Show slave status
 Load Data From Master ; # MyISAM only. Locks Tables on master
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REPLICATION FAILOVER
 Does not happen automatically
 Many solutions exist like virtual IP, Sun
Cluster, Linux-HA Heartbeat, etc
 Application should retry
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MYSQL CLUSTER HIGHLIGHTS
 Synchronous
 Ultra High Availability
 Think Telecom, Banking
 Memory (mostly) and Disk based
 No Single Point Of Failure
 Automatic Failover
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MYSQL CLUSTER ARCHITECTURE
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MYSQL CLUSTER NODEGROUP
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MYSQL CLUSTER SIMPLE CONFIG
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MYSQL CLUSTER NOTES
 ACID transactions
 Supports READ COMMITTED only
 Synchronous replication uses 2 Phase Commit
 Local and Global Checkpoints to disk
 Data access through SQL or NDB API
 Online Backups supported
 All nodes same architecture – big endian or little endian
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MYSQL CLUSTER NOTES (CONTD)
 Max number of data nodes = 48;
 Max(data nodes + management nodes )=63
 Max total number of all = 256 (including SQL nodes)
 Tables highly recommended to have primary keys for
cluster replication.
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MYSQL CLUSTER CONFIGURATION
 NDB config File = config.ini
 Number Of Replicas : 1 upto 4 [ usually 2 ]
 Memory Sizing
 Per Node Memory = (DataSize * Replicas * 1.1) / Nodes
 Default Port number for Mgmt Node = 2202
 Default Port Number for Data Node = 1186
 SQL Node Config File = my.cnf
 [mysqld]
 ndbcluster
 ndb-connectstring=mgmt-hostname
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NODE FAILURE DETECTION
 Uses Heartbeats
 Failed Node Excluded
 Node taken over by another in same node group
 Failed node tries to repair itself and then joins
cluster
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NETWORK PARTITIONING
 Also Called Split Brain condition
 2 Sets of Nodes Diverges with writes
 Management node acts as arbitrator by default
 Nodes with maximum votes survive
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CLUSTER CHECKPOINTS
 Transactions Commits in memory
 Local checkpoint writes all node data and UNDO
log written to disk; old REDO logs can be deleted
 Global Checkpoint: Frequency controlled by
TimeBetweenGlobalCheckpoints (default 2000
millisecs)
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CLUSTER COMMANDS
 ndb_mgmd –f config.ini # start management daemon
 ndbd --connect-string=mgmt_hostname # start data node
 mysqld_safe & # Start SQL node
 ndb_mgm -c mgmt_hostname –e “show”
 mysql> show engine ndb status;
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CLUSTER ROLLING
UPGRADE/DOWNGRADE
 Online Upgrae/Downgrade supported.
 Shutdown node, replace binary, bring it up
 One node at a time in this order:
 Management Node(s)
 Data Nodes
 SQL Nodes
 Watch out for upgradability/downgradbility of
versions
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REPLICATING CLUSTERS
Note: Row-based logging must be enabled for this to work
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ANOTHER HA SOLUTION:
DISTRIBUTED REPLICATED BLOCK
DEVICE
 Available on Linux. Provides synchronous data copy.
 Uses virtual block device
 Replicated from primary server to secondary
 Implemented with kernel level and user level software
 Often used with Heartbeat Linux Cluster manager
 Secondary server is passive – Not for load balancing
 Like RAID but software based
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RESOURCES …
 Developer Zone: Developer Articles, etc.
 http://dev.mysql.com
 MySQL White Papers
 http://www.mysql.com/why-mysql/white-papers/
 MySQL Forums:
 http://forums.mysql.com
 Planet MySQL – Blog aggregator
 http://planetmysql.org
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THAVA ALAGU
Blog: http://blogs.sun.com/thava/
thavamuni.alagu@sun.com
Twitter: thavamuni
Oct 2008