Overview of Global Data Services in oracle 12c
This article should give you an overview of the new feature in Oracle 12c – Global Services. We are aware of database services in oracle. These services provide a workload management by ensuring that clients connect to the optimal instance which is offering the service. It also serves the purpose of high availability by failing over the client connections to the other survival instances that are offering the same service. This is referred to as local data services.
Oracle 12c came up with a new feature of Global Data Services which extends the above feature with automated and centralized workload management across the set of replicated databases like dataguard, golden gate. In addition to this, GDS provides replication lag based workload routing, role based global services and region based global services. Note that the global services can be configured only for databases of version 12c. For databases prior 12c, only local data services can be configured.
One of the major question that would be raised is the difference between local and global data services – A global data service is created across a set of multiple databases, whereas local data services is created only across a set of instances of a single database. With local data services, there is more of manual intervention needed such as a local data service for a standby needs to be first created on the primary database and then on the standby database. Whereas, with GDS, it’s managed globally with a single service.
A global data service configuration consists of some of the major components.
GDS Pool: A GDS Pool is a set of databases containing replicated data in the GDS configuration that provide unique Global Data Services and are administered by different administrator.
A database can belong to only one GDS pool. All databases in a GDS pool need not provide the same global service, but all databases that provide the same global service must belong to the same GDS pool.
GDS Catalog: Just as we have a catalog database in RMAN which acts as a repository for the backup configuration of the registered database, likewise, a GDS Catalog is a repository that is used to store the GDS configuration. This catalog must reside in an oracle database of version 12c.
This database may reside inside or outside the GDS configuration. Please note that a catalog is associated with only one GDS configuration.
GSM (Global Service Manager): As the name says, GSM serves the role of a manager in managing the Global services, failover and load balancing of global services.
It acts as a middle layer between the clients and the databases, just as a remote listener does in RAC databases. In addition to this, it measures the network latency between regions of the configuration by collecting the performance metrics from the databases in the configuration, monitors the databases and global services in the GDS configuration and notifies the clients when they fail.
Client first connects to the GSM and requests for a connection to the global service. The GSM, then, forwards the connection request to the database instance in the GDS configuration that is offering the requested Global Service.
GDS Region: A GDS region is a set of databases within the GDS configuration and the clients that share a very little network latency. A region can contain multiple GDS pools.
You can configure, modify, start or stop global services using GDSCTL utility. To use this, you need to download and install the Oracle Global Service Manager software from the Oracle site.
In the coming posts, we shall see on the installation of GSM software, configuring global services for the databases, how Global Services work with Dataguard and how effective it serves when there is a replication lag.
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