[HA-JDBC] Changing the weight of an active database

[Steve J. <ste...@eu...>]

In our usage of HA-JDBC we are using the simple balancer type to direct
requests to the node with the highest weight.

At runtime nodes can be activated and deactivated and we want to be able
to change the node weights to direct traffic to the "primary" node.

For example, we may start off with:

 Node A : weight 2
 Node B : weight 1

If node A is deactivated, we would want the nodes to be:

 Node B : weight 2

so any nodes activated subsequently will have lower weights. At the
moment we would have to deactivate B in order to change the weight. 

>From a very quick review it looks as though it is safe to change the
weight when active so I am wondering if this is a valid use case for
which I could submit a pull request. 

As far as implementation goes I assume that if the weight could be
changed when active then the dirty flag should not be set and the weight
field should be declared volatile.

Thanks,
Steve