Use the following guidelines to help determine when to
create a new high availability group policy, and when to modify or
delete an existing policy.
Do not delete the default IBM® provided
policies
If you want to override one of the default policies
that IBM provides, it is recommended that you do not delete the current
policy. Instead, create a new policy with more specific match criteria.
The policy with the greatest number of matches is the one that is
used. Not deleting the IBM provided policy enables you to revert back
to that policy if a problem occurs with your new policy.
Do not try to change the type of an existing policy
After a policy for a high availability group is created,
you can change some of the policy attributes such as preferred servers,
or failback, but you cannot change the policy type. If you need to
change the policy type, you must create a new policy and then use
match criteria to associate it with the appropriate high availability
group. The High availability group policy selection process topic
describes how the high availability manager selects a policy for a
high availability group.
Do not change a policy associated with a high availability
group
A component does not necessarily support all policy types
and options. Therefore, before changing the policy that is associated
with a given high availability group, make sure you fully understand
if the application server code using that high availability group
supports the change. For example, if you want to change the type
of policy that is associated with the high availability group used
by the transaction manager component, make sure the transaction manager
code supports the new policy type before making the change.
Do not use the same match criteria for multiple policies
in the same core group
If you have multiple policies configured
with identical match criteria, the policy match to the associated
high availability group is ambiguous. If you are creating a new policy
to replace an older policy that you created, you might need to delete
the older policy to specify the appropriate match criteria. Another
alternative is to specify additional match criteria in each policy
so no ambiguity exists as to which policy is controlling the high
availability group.