The server pool is a new feature in Oracle Clusterware 11gR2. A server pool is the logical division of the cluster into pools of servers for effective resource utilization. Server pools are used to create Policy Managed Databases.
A Policy-Managed database is dynamic with instances managed automatically based on resource requirement for expected workload where as Admin-Managed databases result in instances tied to specific servers.
Policy-Managed database facilitates easy allocation of resources to specific workload and simplifies the consolidation of Databases and Applications on Clusters.
Need for Policy Managed Databases (Server Pool):
As the number of nodes becomes huge, DBA’s tasks became very complicated.
It was not possible to add more instances dynamically to newly added servers.
It was not possible for additional instances of database to start automatically if any servers in the cluster became idle.
It was not possible for a service to be available on newly added nodes dynamically.
Default Server Pools:
There are 2 default pools after a Grid Infrastructure Installation:
Free – any unassigned nodes
Generic – for administrator-managed databases
Attributes Used for Server Pool:
Each pool will be assigned with some attributes are as follows:
IMPORTANCE (priority): The importance specifies the relative importance between the server pools. Default value is 0 to 1000.
MAX_SIZE: The maximum number of servers that can run in a server pool. Default value is 0 or -1 which indicates that all the servers in the cluster can be a part of this pool.
MIN_SIZE: The minimum number of servers that should run in a server pool. If the number of servers contained in a server pool is below the minimum size specified in this attribute, then Oracle Clusterware automatically moves servers from other pools into this one until that minimum number of server is met. The default value is 0.
Allocation of servers:
If a server leaves the cluster for any reason, a server reallocation takes place. If there are servers in the Free Pool and another server pool falls below its maximum value, a free server is allocated to the affected server pool. If there are no free servers, then server reallocation takes place only if a server pool falls below its minimum level. If that occurs, a server will be sourced from one of the following locations in the following order:
The server pool with the lowest importance that has more than its minimum number of servers
The server pool with the lowest importance that has at least one server and has lower importance than the affected server pool
Using these mechanisms, server pools can maintain an optimal level of resources based on current number of servers that are available.
Advantages of Server Pool:
Distribute a uniform workload over several servers in the cluster.
In server pool, the host of the cluster are added and removed from the pools more easily; it has taken off the burden from the DBA’s for the allocation of host in the cluster.
With few attributes which takes care of the whole cluster became much easier for the administration, especially when the number of nodes go beyond two digits.
Posted on behalf of Manjusree | 4iapps.com