I think the initial plan should be to:

1. add a @TenantDiscriminatorColumn annotation to allow configuring the column that holds this value, and
2. to simply interpret the lack of such an annotation to mean that the data is shared.

I tend to think the option between param/literal ought to be per-SessionFactory. If not, we'd have to add a parameter on @TenantDiscriminatorColumn to specify which.

The alternative to interpreting the lack of @TenantDiscriminatorColumn meaning it is shared would be adding a new annotation to indicate that. Something like @SharedTenancy.