In the context of JCA 1.0, maybe this question should be "Is the ManagedConnectionFactory a singleton?". I checked the JCA 1.0 spec, and found that they state the ManagedConnectionFactory be unique.
Thanks,
Greg.
ManagedConnectionFactory is a factory of both ManagedConnection and ConnectionFactory instances.
for each ConnectionFactory created (when you feploy *-ds.xml) a ManagedConnectionFactory is created.