How Oracle Clusterware Assigns New Servers Using Server Pools

Oracle Clusterware assigns new servers to server pools in the following order:

  1. Generic server pool

  2. User-created server pool

  3. Free server pool

Oracle Clusterware continues to assign servers to server pools until the following conditions are met:

  1. Until all server pools are filled in order of importance to their minimum (MIN_SIZE).

  2. Until all server pools are filled in order of importance to their maximum (MAX_SIZE).

  3. By default, any servers not placed in a server pool go into the Free server pool.

    You can modify the IMPORTANCE attribute for the Free server pool. If the value of the IMPORTANCE attribute of the Free server pool is greater than one or more of the other server pools, then the Free server pool will receive any remaining servers once the value of their MIN_SIZE attribute is met.

When a server joins a cluster, several things occur.

Consider the server pools configured in Table 3-2:

Table 3-2 Sample Server Pool Attributes Configuration

NAME IMPORTANCE MIN_SIZE MAX_SIZE PARENT_POOLS EXCLUSIVE_POOLS 
sp1
 
1
 
1
 
10

 

 

 
sp2
 
3
 
1
 
6

 

 

 
sp3
 
2
 
1
 
2

 

 

 
sp2_1
 
2
 
1
 
5
 
sp2
 
S123
 
sp2_2
 
1
 
1
 
5
 
sp2
 
S123

For example, assume that there are no servers in a cluster; all server pools are empty.

When a server, named server1, joins the cluster:

  1. Server-to-pool assignment commences.

  2. Oracle Clusterware only processes top-level server pools (those that have no parent server pools), first. In this example, the top-level server pools are sp1, sp2, and sp3.

  3. Oracle Clusterware lists the server pools in order of IMPORTANCE, as follows: sp2, sp3, sp1.

  4. Oracle Clusterware assigns server1 to sp2 because sp2 has the highest IMPORTANCE value and its MIN_SIZE value has not yet been met.

  5. Oracle Clusterware processes the remaining two server pools, sp2_1 and sp2_2. The sizes of both server pools are below the value of the MIN_SIZE attribute (both server pools are empty and have MIN_SIZE values of 1).

  6. Oracle Clusterware lists the two remaining pools in order of IMPORTANCE, as follows: sp2_1, sp2_2.

  7. Oracle Clusterware assigns server1 to sp2_1 but cannot assign server1 to sp2_2 because sp2_1 is configured to be exclusive with sp2_2.

After processing, the cluster configuration appears, as follows

Table 3-3 Post Processing Server Pool Configuration

Server Pool Name Assigned Servers 
sp1

 

 
sp2
 
server1
 
sp3

 

 
sp2_1
 
server1
 
sp2_2