Toasting more system-table columns

I find the following varlena (ie, potentially toastable) columns
present in the system tables:

relname | attname | typname | attstorage
----------------+--------------+----------+------------
pg_aggregate | agginitval | text | x
pg_attrdef | adbin | text | p
pg_attrdef | adsrc | text | p
pg_class | relacl | _aclitem | m
pg_database | datpath | text | p
pg_description | description | text | x
pg_group | grolist | _int4 | p
pg_index | indpred | text | x
pg_language | lancompiler | text | x
pg_proc | probin | bytea | p
pg_proc | prosrc | text | p
pg_relcheck | rcbin | text | p
pg_relcheck | rcsrc | text | p
pg_rewrite | ev_action | text | x
pg_rewrite | ev_qual | text | x
pg_shadow | passwd | text | p
pg_statistic | stacommonval | text | x
pg_statistic | stahival | text | x
pg_statistic | staloval | text | x
pg_trigger | tgargs | bytea | p
pg_type | typdefault | text | p

Of these tables, only pg_rewrite has a toast table so far.

Offhand it would seem to be a good idea to create toast tables for
pg_attrdef, pg_description, pg_proc, pg_relcheck, possibly pg_statistic.
Certainly a toast table for pg_proc is a must so that we can deal with
large procedure bodies. Toasting pg_attrdef would allow very large
column default expressions (dubious value), pg_description for long
comments (probably should have this), pg_relcheck for long constraint
expressions (probably want this), pg_statistic to cope with long
min/max/common values (not sure about this).

I doubt the other system tables need toast tables, although we may as
well mark all of these attributes "m", ie, they should be compressible
in-line even if there is no toast table.

Comments?

regards, tom lane