Re: Proposal for Allow postgresql.conf values to be changed via SQL

Robert Haas <robertmhaas@gmail.com> writes:
> On Mon, Dec 3, 2012 at 6:38 AM, Amit Kapila <amit.kapila@huawei.com> wrote:
>> opt_persistent: PERSISTENT                                { $$ = TRUE; }
>> | /*EMPTY*/                %prec Op        { $$ = FALSE; }
>> ;
>> 
>> I am not sure if there are any problems with above change.

> We usually try to avoid operator precedence declarations.  They
> sometimes have unforeseen consequences.

Yes.  This is not an improvement over factoring out opt_persistent as
I recommended previously.

>> Found one difference with the change is, the command "reset persistent"
>> execution results in different errors with/without change.
>> 
>> without change:
>> unrecognized configuration parameter "persistent".
>> with change:
>> syntax error at or near ";"

> ...but this in itself doesn't seem like a problem.

Indeed, this demonstrates why kluging the behavior this way isn't a good
solution.  If PERSISTENT is an unreserved word, then you *should* get
the former error, because it's a perfectly valid interpretation of the
command.  If you get the latter then PERSISTENT is not acting like an
unreserved word.
        regards, tom lane