Core group policy settings

 

+

Search Tips   |   Advanced Search

 

To define a policy for a high availability group, click...

Servers | Core groups | Core group settings | New or existing core group | Policies | policy_name

A policy is defined at the core group level and applies to matching high availability groups contained within the core group

Name

Name of the policy. This name must be unique within the scope of a core group.

Policy type

Policy type that was selected when this policy was created. This is a read-only field. To change the policy type, delete this policy and then create it again specifying a different policy type. If this is an IBM provided policy, do not delete it. Instead create a new policy and specify more of the attributes contained in the name of the high availability group as the match criterion for this new policy. The policy with the greatest number of matches to attributes in a group's name is the policy that is associated with that group.

Description

Specify a description of this policy. For example, the clustered TM policy provided with the product has "TM One-Of-N Policy" as its description.

Is alive timer

Specifies, in seconds, the interval of time at which the high availability manager will check the health of the active group members that are governed by this policy. If a group member has failed, the server on which the group member resides is restarted. The high availability manager detects two fundamentally different kinds of failures.

  • An entire process failure. This failure detection is accomplished using functions such as the heartbeat timers. This type of detection does not involve the Is alive timer function. If an entire process fails, it will be detected and the various high availability groups will fail over to other servers in the core group.

  • An application or program failure. If, for some reason. an application or a program, like the transaction manager or a service integration bus function hangs, the high availability manager will eventually detect the hang. The amount of time that might pass before the hang is detected is determined by the value specified for the Is alive timer parameter. The parameter controls how often the high availability manager will call back to the component that created the high availability group member and ask if it is still alive. This allows detection of hung code or program errors that somehow do not cause the entire process to stop functioning or terminate.

Data type Integer

  • Valid values are -1 to 600 seconds, inclusive.

  • If -1 (negative 1) is specified, this function is disabled.

  • If 0 (zero) is specified, the frequency at which the high availability manager checks the health of the active group members is determined by the time interval specified at the application server process level.

  • If a value larger than 0 (zero) is specified, the high availability manager uses the time interval specified here, instead of the one specified at the application server process level, when determining how frequently it should check the health of the high availability group members using this policy.

Default 0 (zero)

Quorum

Specify whether quorum checking is enabled for a group governed by this policy. Quorum is a mechanism that can be used to protect resources that are shared across members of the group in the event of a failure.

Quorum is an advanced hardware function and should not be enabled unless you thoroughly understand how to properly use this function. If not used properly, this function can cause data corruption. The Quorum setting in the policy will only have an effect if the following items are true:

When enabled, any group using this policy will not achieve quorum until a majority of the members are running. For example, if there are n members in the group, (n/2) + 1 servers must be online in order to achieve quorum. No group members will be activated until quorum has been achieved.

The quorum mechanism is designed to work in conjunction with a hardware control facility that allows appservers to be shut down if a failure causes the group to be partitioned.

Fail back

Specify whether work items assigned to the failing server are moved to the server that is designated as the most preferred server for the group if a failure occurs. This field only applies for M of N and One of N policies.

Preferred servers only

Specify whether group members are only activated on servers that are on the list of preferred servers for this group. This field only applies for M of N and One of N policies.

Number of active members

Specify how many of the high availability group members are to be activated. This field only applies for the M of N policy.

Additional Properties

Specifies one or more of the following options, depending on the type of policy you selected:

Custom properties Click to specify custom properties for the policy.
Match criteria Click to set up a match criterion for the policy.
Preferred servers Click to set up a list of servers that are given preference when group members are activated.
Static group servers Click to set up a list of the specific servers that are activated.



 

Related tasks


Creating a policy for a high availability group