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| − | '''How master-slave replication works:'''
| + | Documentation how replication and clustering in Reddwarf works should go here. |
| − | * Replication in mysql works basically via log shipping.
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| − | * The mysql master logs all data manipulation events in the mysql binary log.
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| − | * 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.
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| − | * Binary logging should be turned *on* on the master and *off* on the slaves.
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| − | * 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.
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| − | * there are 2 internal mysql threads that exist on the slave, the SQL thread and the IO thread
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| − | * the IO thread is responsible for getting binary events from the master and the SQL thread is responsible for applying them locally.
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| − | * slaves should be read-only, allowing data manipulation statements on slaves will result in corrupt or out of sync slaves
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| − | '''How to know that replication broke:'''
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| − | * parse the output of "SHOW SLAVE STATUS" on the replicated slave.
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| − | * the IO thread is set to No
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| − | * the SQL thread is set to No
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| − | * the seconds_behind_master is > a set number and isn't reducing over time (this is a conditional case that we need to define).
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| − | * This case is a failure because it means that for whatever reason the slave will never be in sync with the master.
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| − | * This can be due to the slave not having enough resources to keep up or that the master has too many slaves.
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| − | * 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.
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| − | '''Steps to setup replicaiton:'''
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| − | No point in rewriting known steps, follow instructions here: [http://dev.mysql.com/doc/refman/5.1/en/replication-howto.html MySQL Replication Documentation]
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