Обсуждение: question about the design consideration for system catalogs

Howdy,

I have a question about the design consideration for system catalogs.
Some of tables include arrays to hold the variable informations, such
as tracking the procedure declaration informations in pg_proc. To store
the informations for procedure parameters, there are proargtypes,
proallargtypes, proargmodes and proargnames colums.
Store the parameters in this way is much easier to access these
informations for backend developper. Each procedure informations can be
retrieved just in one query and store them in the Form_pg_proc structure
directly.
But if I wanna check the parameter informations, it's a little hard to
read. If I wanna write a program to re-construct the procedure source
code, it is not convenience to access the parameter informations from
the front-end. What cons are there If store the procedure and its
parameters in different tables(e.g. pg_attribute and pg_attrdef)? Access
two tables is slower than access one tables? It needs more code to
access the procedure informations?
I think store them separately is more common.

TIA 

"Tao Ma" <feng_eden@163.com> writes:
> But if I wanna check the parameter informations, it's a little hard to
> read. If I wanna write a program to re-construct the procedure source
> code, it is not convenience to access the parameter informations from
> the front-end. What cons are there If store the procedure and its
> parameters in different tables(e.g. pg_attribute and pg_attrdef)?

Loss of backwards compatibility, for one thing.  We're not going to
redesign those catalogs just because somebody thinks some other layout
would be more convenient for one purpose --- it would break a lot of
code for little gain.
        regards, tom lane

"Tom Lane" <tgl@sss.pgh.pa.us> wrotes:
> "Tao Ma" <feng_eden@163.com> writes:
>> But if I wanna check the parameter informations, it's a little hard to
>> read. If I wanna write a program to re-construct the procedure source
>> code, it is not convenience to access the parameter informations from
>> the front-end. What cons are there If store the procedure and its
>> parameters in different tables(e.g. pg_attribute and pg_attrdef)?
>
> Loss of backwards compatibility, for one thing.  We're not going to
> redesign those catalogs just because somebody thinks some other layout
> would be more convenient for one purpose --- it would break a lot of
> code for little gain.
>
Thank you. Actually, I don't want to change anything. I am curious
why we use this form, such as it is easy to access the informations
internally, and so on. Or this form is jsut historical reasons, we
follow the original patterns. I know the system catalogs is very
important and critical to the DBMS. So pls don't mind me and my poor
questions.

TIA