high availability with mysql
DESCRIPTION
TRANSCRIPT
THAVA ALAGU
Staff Engineer, Database Group,
Sun Microsystems, Bangalore
http://blogs.sun.com/thava/
Oct 2008
HIGH AVAILABILITY WITH MYSQL
Welcome !Welcome !
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LET US DISCUSS ABOUT …
Aspects of High AvailabilityAspects of High AvailabilityMySQL ReplicationMySQL ReplicationMySQL ClusterMySQL ClusterApplication HAApplication HAResourcesResources
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ARCHITECTURE OVERVIEW
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HIGH AVAILABILITY
Data Must Not be LostData + 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 ReplicationRow-based ReplicationMixed Based Replication
Depends on MySQL Version, Storage Engine
Can override the defaults e.g. use row-format=row option
Usually row based replication is saferBut 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 failuresFaster Slave with No Transaction Engine
e.g. InnoDB to MyISAMHow:
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 MasterCan Use Blackhole Engine for Master2Use log-slave-updates option at Master2
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MULTIMASTER (AVOID)
2 Masters updating each otherRing of MastersUpdates on disjoint setsUsually, Stay Away
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REPLICATION TOPOLOGIES SUMMARY
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REPLICATE USING SSL
For High SecurityUses Certificate-Authority Certificate,
Server Public Key, Server Private Key
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REPLICATION SETUP UPGRADE
Upgrade Slaves First, Then MasterShutdown, Upgrade, RestartWatch 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’;
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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
REPLICATION FAILOVER
Does not happen automaticallyMany solutions exist like virtual IP, Sun
Cluster, Linux-HA Heartbeat, etcApplication should retry
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MYSQL CLUSTER HIGHLIGHTS
Synchronous Ultra High AvailabilityThink Telecom, Banking Memory (mostly) and Disk basedNo Single Point Of FailureAutomatic 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
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Note: Row-based logging must be enabled for this to work
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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