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Automatic Failover

Data Guard has implemented something called Fast-start Failover(FSFO) which usesthe Broker to perform the failover actions when there is a problem. his architectureuses a third member !uorum that ensures that the failover occurs onl" whenever"thing meets the rules that "ou have de#ned$ when the failover has happened

the primar" will never be allowed to open to avoid an" split%brain scenarios$ thiswould be a bit of a nightmare should both databases be open and processingtransactions.

he third member is called the Observerand its &ob is to maintain a connection withthe primar" and target standb" databases$ monitoring there health and performingan" failover's necessar"$ the Observer will also reinstate the old primar" when itcomes back on$ if it can. he observer pings the primar" database and that the #rstsign of trouble it will start to countdown (which "ou con#gure)$ if it does re%establishthe connection it will make all the necessar" checks before goes back to watch modeagain$ if the timer epires then it checks that the standb" can take over and initiatesa failover$ this switchover will have all automaticall" and in the background using theBroker. f and when the primar" comes back the Observer will reinstate the old

primar" as a standb" database again using the Broker to achieve this.

t is import on where he Observer is placed in the network$ onl" one observer perData Guard installation can be installed$ so this server must have access to both theprimar" and standb" databases with as much redundant networking as possible. *et"our thing is how much is the observer going to cost me$ not much as it can run onmost platforms and onl" re!uired the Oracle +lient ,it for the version of Oracle that"ou are running$ "ou must setup the *S*-/S on the observer to allow it to pingthe databases. f the Observer was to crash it will have no impact on the currentOracle environment$ the onl" impact is that FSFO will not be available until theObserver is up and running again. he Observer can monitoring the following

Database crash

S"stem crash

he loss of the network

+omplete site outage

0ou can also get FSFO to perform a shutdown aborton the primar" when other issuesarise such as

Data#le O1ine

+orrupted +ontrol#le

+orrupted Dictionar"

naccessible 2og#le

Stuck -rchiver

he tags above must be entered as the" are above otherwise the Broker will notunderstand them

onitor a speci#ccondition via theBroker

DGG324 enable fast5start failover condition 6+orrupted +ontrol#le67DGG324 enable fast5start failover condition 6Data#le O1ine67

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o displa" what "ou are monitoring use

Displa" conditionsthat are be monitored

DGG324 show fast5start failover7

Fast%Start Failover8 DS-B2/D

hreshold8 9: secondsarget8 (none)Observer8 (none)2ag 2imit8 9: secondsShutdown ;rimar"8 3

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lag limit DGG324 edit con#guration set propert" FastStartFailover2ag2imit @ A:7

f the data loss is less then the limit the failover will proceed$ if more redo would beloss than the lag limit$ the failover will not occur and nothing happens until theprimar" database either comes back and processing continues or "ou choose tofailover manuall"$ suering the additional data loss. f "ou are using maimumprotection mode then this propert" is ignored.

=ere are two more additional properties that "ou can setup regarding the primar"$one is to shutdown it down if it becomes hung and the other is to reinstate it if afailover does occur

abort primar" if in a hungstate

DGG324edit con#guration set propert"FastStartFailover;m"Shutdown @ true7

reinstate primar" after afailover

DGG324edit con#guration set propert"FastStartFailover-uto3einstate @ true7

Once "ou are happ" with ever"thing "ou can now enable the FSFO

/nable FSFO

DGG324 enable fast5start failover7

EE Displa" the con#guration

DGG324 show fast5start failover7