|
|
| (7 intermediate revisions by the same user not shown) |
| Line 1: |
Line 1: |
| − | == MySQL Master/Slave Replication ==
| + | Documentation how replication and clustering in Reddwarf works should go here. |
| − | | |
| − | '''How master-slave replication works:'''
| |
| − | * Replication in mysql works basically via log shipping.
| |
| − | * The mysql master logs all data manipulation events in the mysql binary log.
| |
| − | * While this is happening the slave instances are connected to the master via TCP and receive the same events and write them to their relay log.
| |
| − | * Binary logging should be turned *on* on the master and *off* on the slaves.
| |
| − | * If binary logging is turned on on the slave you will suffer massive IO hits as each log entry writes to the relay log, then the table, then the binary log.
| |
| − | * there are 2 internal mysql threads that exist on the slave, the SQL thread and the IO thread
| |
| − | * the IO thread is responsible for getting binary events from the master and the SQL thread is responsible for applying them locally.
| |
| − | * slaves should be read-only, allowing data manipulation statements on slaves will result in corrupt or out of sync slaves
| |
| − | | |
| − | | |
| − | '''How to know that replication broke:'''
| |
| − | * parse the output of "SHOW SLAVE STATUS" on the replicated slave.
| |
| − | * the IO thread is set to No
| |
| − | * the SQL thread is set to No
| |
| − | * the seconds_behind_master is > a set number and isn't reducing over time (this is a conditional case that we need to define).
| |
| − | * This case is a failure because it means that for whatever reason the slave will never be in sync with the master.
| |
| − | * This can be due to the slave not having enough resources to keep up or that the master has too many slaves.
| |
| − | * If ever any of these 3 things are true it is assumed that replication is broken and the slave is to be destroyed and recreated.
| |
| − | | |
| − | | |
| − | '''Steps to setup replicaiton:'''<br />
| |
| − | * No point in rewriting known steps, follow instructions here: [http://dev.mysql.com/doc/refman/5.1/en/replication-howto.html MySQL Replication Documentation]
| |
| − | | |
| − | | |
| − | '''Pros/Cons'''
| |
| − | {| class="wikitable"
| |
| − | |-
| |
| − | ! Pros !! Cons
| |
| − | |-
| |
| − | | Standard MySQL || Prior to MySQL 5.6 Replication is brittle (See notes on MyISAM)
| |
| − | |-
| |
| − | | Very well understood || Repairing can be time consuming
| |
| − | |-
| |
| − | | No special architecture needed || Creating new slaves can require downtime or read locking on the master
| |
| − | |-
| |
| − | | Easy to troubleshoot || Only works well for scaling reads
| |
| − | |-
| |
| − | | Works with all storage engines (see notes on MyISAM) || Single threaded, high concurrency on the master can cause issues where slaves can't keep up
| |
| − | |-
| |
| − | | Offers simple and complex configurations for read scaling ||
| |
| − | |-
| |
| − | | Opensource tools available for monitoring/troubleshooting ||
| |
| − | |-
| |
| − | | Great for making backup or reporting slaves ||
| |
| − | |-
| |
| − | | Good general purpose replication ||
| |
| − | |}
| |
| − | | |
| − | ''' Notes: '''
| |
| − | * '''MyISAM:''' The MyISAM engine is not transaction safe and therefore not crash safe. There is a common misconception that MyISAM breaks replication and this is simply not true. A crashed host using MyISAM will cause replication to fail, but the failure lies in the fact that the host crashed not that MyISAM is used. Where MyISAM makes replication recovery difficult is that crash recovery is a manual process and therefore leaves replication in a known bad state until recovered. The important thing to note here is that simply creating a table using the MyISAM storage engine on a replicated host does *not* immediately break replication. While Oracle MySQL hasn't done much to improve MyISAM's crash recovery and fault tolerance the folks at MariaDB are pushing toward that.
| |
