Re: [Tarantool-patches] [PATCH 0/4] session settings fixes

[Peter Gulutzan <pgulutzan@ocelot.ca>]

Hi,

On 2020-04-07 10:32 a.m., Chris Sosnin wrote:
 > Hi!
 >
 >> On 3 Apr 2020, at 20:09, Peter Gulutzan <pgulutzan@ocelot.ca> wrote:
 >>
 >> Hi,
 >>
 >> Re:
 >> SETTING SET "sql_default_engine" = 'memtx';
 >>
 >> Adding a new reserved word SETTING, without advance notice,
 >> should be against policy. It causes a slight risk
 >> of breaking an existing application.
 >>
 >> I had hoped for
 >> UPDATE _SETTINGS_DEFAULT_ENGINE SET VALUE = 'memtx';
 >
 > Implementing this syntax would either require creating a table for 
each setting
 > or adding new keywords, since this is the same as updating tables.
 >

It would definitely require creating a (viewed) table for each setting.
That is why I said "And similarly for sql_defer_foreign_keys etc."

 > Moreover, SET VALUE construction also is not supported, so we still need
 > to reserve a new word.
 >

As I pointed out in my earlier email, I can say
UPDATE _settings_default_engine SET value = 'memtx';
now, in a current Tarantool version, without a parser error.
If _settings_default_engine is not a view, it works fine.
So I didn't see why there is a need to reserve VALUE.

(Digression: That does not mean I like using VALUE for a
column name. I objected about it in an earlier email.
But I did not propose a better name, and now it is too late.)

 > We can borrow another MySQL syntax — SET SESSION name = value
 > What do you think about this option?

In MySQL, SESSION is not a reserved word.
Let us go back to my original complaint.
CREATE TABLE setting (setting INTEGER PRIMARY KEY);
That statement is legal in Tarantool-2.4.
That statement is illegal in branch ksosnin/gh-4712-session-settings-v2.
If you say SET SESSION instead of SETTING SET,
is there still a need to add a new reserved word without notice?

(Digression: Currently, every word that can be the start of a statement
is reserved. Also, a few words that might in future be the start of a
statement are reserved -- ANALYZE, BEGIN, CALL, DECLARE, END, FETCH, FOR,
GRANT, IF, ITERATE, LEAVE, LOOP, RENAME, REPEAT, RESIGNAL, REVOKE, SET,
SIGNAL. I believe that is a good thing. I do not believe that
SETTING should be unreserved if it is the start of a statement.)

Peter Gulutzan