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

[Peter Gulutzan <pgulutzan@ocelot.ca>]

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';
I claim that is just as "user friendly" -- it
adds two words, but it removes quotation marks.
And it does not require that users learn new syntax
because UPDATE ... SET is well known.

Notice that I can already do this -- almost.
This is legal:
CREATE VIEW _SETTINGS_DEFAULT_ENGINE AS
     SELECT "value" AS value
     FROM "_session_settings"
     WHERE "name" = 'sql_default_engine';
The flaw is that views are not updatable.
But I don't regard that as a big problem
because this is not a proposal to make
all views updatable. It only requires:
when you see that exact UPDATE statement,
transform it to box.session._settings:update.
And similarly for sql_defer_foreign_keys etc.

Alternatively, users could create a Lua function
X which updates
_session_settings, vaguely like this
box.schema.func.create('X',
     {language = 'LUA',
      returns = 'string',
      body = [[function ()
box.space._session_settings:update('sql_default_engine', {{'=', 2, 
'memtx'}});
               return 'memtx changed'
               end]],
      is_sandboxed = false,
      exports = {'LUA', 'SQL'},
      is_deterministic = true})
then allow this SQL syntax:
CALL X();
Again, I claim that this is just as "user friendly"
because -- as far as I can tell -- some people think
saving keystrokes is the same as being friendly.
Nikita Pettik explained that issue#4711 is for a shortcut
and that is short.
Eventually we will probably want to support CALL anyway,
and it is already a reserved word.

Thus there are "user-friendly" alternatives that do not
require new proprietary syntax.

Peter Gulutzan