Alex,
about backward compatibility (BC), it's now apparent that choosing to
put a script name inside pma_column_info.transformation was a decision
that has shortcomings.

Maybe there should be some kind of neutral string there, that is not a
script name nor a class name, but just indicates the kind of
transformation. Then, the code would map this string to the exact script
to call.

Ok, that sounds good.

Anyway, we have to decide if the BC will be done by some permanent code
in the transformation logic, or via a conversion script that the user
has to run.

I would say that although the conversion script is easier to implement,

from the users point of view, they would have to make an additional

step to maintain their old databases (at first it won't work and then they

would have to read about it).

Maybe, a version number in pma_column_info would help, to see if
conversion is needed.

When getting a new release of PMA, users can keep their old config

file. Would that mean that some users will have a version number

and others won't?

By permanent code do you mean that the old format will be kept in

pma_column_info for existing transformations and then treated

differently depending on a version number? What happens when a

user modifies an existing transformation, will the same old version

be used?

Alex