Tuesday, 20 January 2015

Failure is not an option

The failure is not an option. Despite this statement is quite pretentious is also the rule number zero of any decent DBA. The task failure, should this be a simple alter table or an emergency restore, is not acceptable. The database is the core of any application and therefore is the most important element of the infrastructure.

In order to achieve this impossible level, any task should be considered single shot. Everything must run perfectly at the first run like if without rollback plan. However the rollback procedure must be prepared and tested alongside with the main task on the test environment in order to get a smooth transition if the rollback should happen. It's also very important to remember the checklist. This allow the DBA to catch the exact point of any possible failure ensuring a rapid fix when this happens.

Having a plan B gives a multiple approach for the task if something goes wrong. For example, when dealing with normal size databases* is possible to implement many strategies for the disaster recovery having a similar time needed for the recovery. When the amount of data becomes important this is no longer true. For example a logical restore takes more time than a point in time recovery or a standby failover. In this case the plan A is the physical restore.If this does not work then the logical recovery should be used instead.

 * I consider normal sized any database under the 500 GB

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