Server Pools

Server Pools

Server pools are logical divisions of a cluster into pools of servers or nodes. They:

• Distribute a uniform workload over several servers in the cluster
• Are allocated to host databases or other resources
• Are managed using the crsctl and srvctl commands
• Support parent-child relationships among server pools
• Top-level pools are mutually exclusive.
• Include two built-in server pools at Oracle Clusterware installation:
• FREE: For servers that are not assigned to other pools
• GENERIC: For administrator-managed fixed configuration and pre-11g Release 2 databases

Server Pool Attributes

Server pool attributes can be specified when you create a server pool, or they can be modified after a server pool has already been created. The only required attribute is NAME. The optional attributes include:

• ACL: Defines the owner of the server pool and what privileges are granted to various operating system users and groups. The value of this attribute is populated at the time a server pool is created based on the identity of the process creating the server pool, unless explicitly overridden. It uses a string in the format of: owner:user:rwx,pgrp:group:rwx,other::r— to specify allowed privileges for the owner, group, and other users. The privileges allowed for a server pool are read-only (r), the ability to modify attributes or delete the server pool (w), and the ability to assign resources to the pool (x).

• ACTIVE_SERVERS: Is a space-delimited list of servers that are currently assigned to the server pool. This attribute is automatically managed by Oracle Clusterware.
• EXCLUSIVE_POOLS: Governs whether servers assigned to this server pool are shared with other server pools. This attribute is a string value containing any arbitrary string. Any other server pool that has the same value for this string is mutually exclusive with this server pool. 
• IMPORTANCE: Determines the relative importance of the server pool compared to other server pools, with 0 denoting the lowest level of importance and 1000 the highest level of importance. The default value is 0.
• MAX_SIZE: Determines the maximum number of servers a server pool can contain. A value of –1 for this attribute spans the entire cluster and is the default value.
• MIN_SIZE: Determines the minimum number of servers a server pool can contain. The value of this attribute does not set a hard limit. It governs the priority for server assignment. The default value is 0.
• PARENT_POOLS: Allows the creating of nested server pools. Server pools listed in this attribute are referred to as parent server pools. Multiple parent server pools may be specified by using a comma-delimited list of server pool names.
• SERVER_NAMES: Lists the candidate node names upon which servers reside that may be associated with a server pool. If this attribute is empty, Oracle Clusterware assumes that any server may be assigned to any server pool, to the extent allowed by other attributes, such as PARENT_POOLS.

Note: All attributes of the GENERIC server pool are read-only and cannot be modified. For the FREE server pool, only the IMPORTANCE and ACL attributes can be edited.

Use the crsctl status server command to check the server status:
# crsctl status server -f

Introduction to 11gR2 RAC ServerPools