Re: Add support to COMMENT ON CURRENT DATABASE

On Tue, Jan 3, 2017 at 12:06 AM, Ashutosh Bapat
<ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
> Instead of changing get_object_address_unqualified(),
> get_object_address_unqualified() and pg_get_object_address(), should
> we just stick get_database_name(MyDatabaseId) as object name in
> gram.y?

No. Note this comment at the top of gram.y:

* In general, nothing in this file should initiate database accesses
* nor depend on changeable state (such as SET variables). If you do
* database accesses, your code will fail when we have aborted the
* current transaction and are just parsing commands to find the next
* ROLLBACK or COMMIT. If you make use of SET variables, then you
* will do the wrong thing in multi-query strings like this:
* SET constraint_exclusion TO off; SELECT * FROM foo;
* because the entire string is parsed by gram.y before the SET gets
* executed. Anything that depends on the database or changeable state
* should be handled during parse analysis so that it happens at the
* right time not the wrong time.

I grant you that MyDatabaseId can't (currently, anyway) change during
the lifetime of a single backend, but it still seems like a bad idea
to make gram.y depend on that. If nothing else, it's problematic if
we want to deparse the DDL statement (as Fabrízio also points out).

--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company