Re: [v9.2] SECURITY LABEL on shared database object

2011/7/5 Alvaro Herrera <alvherre@commandprompt.com>:
> Excerpts from Kohei Kaigai's message of mar jul 05 11:46:06 -0400 2011:
>> > On Tue, Jul 5, 2011 at 10:49 AM, Alvaro Herrera
>> > <alvherre@commandprompt.com> wrote:
>> > > Excerpts from Robert Haas's message of mar jul 05 10:19:18 -0400 2011:
>> > >
>> > >> Hmm, OK.  I guess what I'm not sure about is - how much should we
>> > >> worry about the fact that this creates several more shared (and
>> > >> therefore nailed?) system catalogs?  Anyone have an opinion on that?
>> > >
>> > > "Several"?  That would worry me, given that we currently have a small
>> > > number (eight currently).  If it's just one more, I don't think it's
>> > > such a big deal.  I'm not sure what you mean by nailed though -- I mean,
>> > > for example pg_shdescription is shared but not nailed in the rd_isnailed
>> > > sense of the word, AFAICS.
>> >
>> > Well, right now the patch has pg_shseclabel, and its index, plus a
>> > toast table and a toast index.  Not sure why we want/need the toast
>> > table & index there, but the patch has 'em as of now.
>> >
>> As a common belief, TEXT is a variable length data type, so pg_shseclabel
>> need to have its toast table. However, I don't expect the label field get
>> represented as a reference to external pointer, because average length of
>> security context is about 40-60 bytes much less than the threshold to
>> launch toast_save_datum().
>> Do I need to remove these toast table & index?
>
> We don't have toast tables for pg_database and so on, for example, which
> means that datacl cannot go over a few hundred bytes long.  I think it
> makes sense to not have toast tables for pg_shseclabel.  Keep in mind
> that the label might be compressed before it's stored out of line, which
> gives you quite a bit of actual space.  If a security context is over
> 5000 bytes in length I think you're in trouble :-)
>
The attached patch removes toast table & index for pg_shseclabel.

The current toasting.h defines toast table & index on pg_database,
pg_shdescription and pg_db_role_setting only.
The pg_authid and pg_tablespace don't have toast table & index
in spite of variable-length field.
So, it might not be a necessary stuff for all the shared relations.

Thanks,
--
KaiGai Kohei <kaigai@kaigai.gr.jp>