RFC: Moving specific attributes from pg_attribute column into attoptions

Hi hackers!

While working on Pluggable TOAST we extended the PG_ATTRIBUTE table with a
new
column 'atttoaster'. But is is obvious that this column is related to
tables, columns and datatypes
only, and is not needed for other attributes.
You can find full discussion on Pluggable TOAST here
https://www.postgresql.org/message-id/flat/224711f9-83b7-a307-b17f-4457ab73aa0a(at)sigaev(dot)ru

We already had some thoughts on storing, let's call them "optional"
attributes into 'attoptions'
instead of extending the PG_ATTRIBUTE table, and here came feedback from
Andres Freund
with a remark that we're increasing the largest catalog table. So we
decided to propose moving
these "optional" attributes from being the PG_ATTRIBUTE column to be the
part of 'attoptions'
column of this table.
The first most suspected attributes to store in attoptions column are the
'atttoaster' and
'attcompression', because they are related to datatypes and table columns.
Also, this change
will allow setting options for custom Toasters, which makes a lot of sense
too, according with
an important [as we see it] 'force TOAST' option which is meant to force
given value to be
TOASTed bypassing existing logic (reference depends on tuple and value
size).

Also, we suggest that options stored in 'attoptions' column could be packed
as JSON values.

It seems to make a lot of sense to optimize PG_ATTRIBUTE structure and size
with attributes
related only to specific types, etc.

We'd welcome any opinions, suggestions and advice!

--
Regards,
Nikita Malakhov
https://postgrespro.ru/