At this point the physical standby database is closed and the final log switch is done without allowing the primary database to advance the sequence numbers for each thread.Īfter the EOR redo is sent to the standby databases, the original primary database is finalized as a standby and its control file backed up to the trace file and converted to the correct type of standby control file. A special switchover marker called the EOR (end of redo) is then placed in the header of the next sequence for each thread, and the online redo files are archived a second time, sending the final sequences to the standby databases. When the switchover command is executed the redo generation is stopped, all DML related cursors are invalidated and users are either prevented from executing transactions or terminated and he current redo log is archived for each tread. start the switchover (primary)Īlter database commit to switchover to standby You always start the switchover on the primary database, the actual switchover command is below whether you are using Grid Control, Broker or SQLPlus. Once the switchover is complete the redo from the new primary will send it to the remaining standby servers, including the old primary, if using either grid control or the broker this should be all automatically do for you, but if you are using SQLPlus you have to performance some manual work. This planned event normally happens during a quiet period, the reason for the switchover might be DR testing, patch, hardware changes, implementing RAC, etc. The switchback does not exists as it is a switchover but in the reserve order, which would restore the database back on its original server. Switchover is the act of change the standby database into the primary but in a controlled manor, the planned event means that it is safe from data loss because the primary database must complete all redo generation on the production data before allowing the switchover to commence. Role transition is divide into two types switchover and failover, they also might be called switchback, failback but they all mean the the same thing to transition the state of Data Guard from one state to another. This section is what Data Guard is really all about, its about a standby database taking over the production database, and how to revert back when problems have been fixed.
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