dataguard主库failover业务应用自动切换到备库

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2019-10-13

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Easy Application Failover with DataGuard

Application failover when database failover or switchover is facilitated by Data Guard. This is not

the real seamless failover but works perfect for most of the scenarios...

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1. PREFACE

This tutorial covers the situation where an application still has to be able to connect to the primary

database after a failover or a switcover is initiated on a dataguard system. This is not the actual

seamless application failover. It does not employ any clusterware components like FAN or TAF. That

is why I call this "EASY" Application Failover. It may actually have a different name but I didn't come

across with an Oracle document about it... so it is "Easy Applcation Failover with Datagaurd" for me.

2. HOW IT WORKS

The below diagram shows the architecture of the setup.

The logic behind the application continuity in the case of a swithover (or failover) depends on a

virtual service that can be started or stopped with a trigger depending on the role of the database

server. To be more precise, we should implement a role based service that will only be enabled when

the database server is in primary role. In fact, from the version 11.2 on, this role based service is not

handled by triggers but the clusterware as follows:

srvctl add service -db orcl -service vservice -role primary

However, it might be the case that we are working on a single instance database without a

clusterware, so the trigger methodology can still be used.

As a result, the service name that the application should be using, would be active only on the

primary side at a given time. Even the application may try to go to the standby (if it is the first

connection defined), it will see that there is no such service and proceed to the next adress in the list.

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