> Let me go over the issues with the varchar() change.
>
> char() will continue to store full bytes, while varchar() function like
> text, but with a limited length.
>
> Now, pg_attribute.attlen is access everywhere, trying to find out how
> long the data field is. With text, the length is -1, but with varchar
> currently, it is the max length, and hence, it has to store all those
> bytes.
>
> Now, my idea is to add a new pg_attribute column called 'attmaxlen'
> which will hold the maximum length of the field. char() and varchar()
> will use this field, and the code will have be changed. Cases where
> attlen is referenced to determine data size will continue to use -1, but
> references to all functions that create a data entry will use the
> attmaxlen. I see 124 references to attlen in the code. Not too bad.
> Most are obvious.
>
> We had some of this work in the past, fixing places where the size was
> not properly passed into the table creation code, because varchar() and
> char() do not have lengths defined in pg_type like everyone else, but it
> is only in pg_attribute.
>
> This is a related change to allow data reference and tuple max length
> reference to be separate. I can see other new types using this field
> to.
>
> Come to think of it, I wonder if I could have the disk copy of
> pg_attribute use the pg_type length, and use the pg_attribute length
> only when creating/updating entries? I wonder if that is what it does
> already. Looks like that may be true.
>
> Comments?
Is what you are trying to do related to what could be used to implement
other (SQL92) data types like numeric(precision,scale) where there are one
or two additional parameters which are assigned when a column/class/type is
defined and which must be available when working with column/class/type
instances? We probably don't want to do anything about the latter for v6.3
(spread pretty thin with the work we've already picked up) but I'd like to
do something for v6.4...
Oh, while I'm thinking about it, this kind of thing is probably also
necessary to get arrays working as expected (enforcing dimensions specified
in the declaration).
- Tom
