M2: adodb sessions switched to moodle sessions

adodb sessions are not working at all in 1.9.x and before, because it lacks session locking code (== multiple open windows or linked files override each others changes)
we need something better in 2.0

Getting the following notices and warnings from tablelib code. They just started a few days ago after an update of HEAD :

Notice: Indirect modification of overloaded property moodle_session::$flextable has no effect in C:\Users\Pratt\workspace\moodle-HEAD\lib\tablelib.php on line 360

Notice: Indirect modification of overloaded property moodle_session::$flextable has no effect in C:\Users\Pratt\workspace\moodle-HEAD\lib\tablelib.php on line 361

Notice: Indirect modification of overloaded property moodle_session::$flextable has no effect in C:\Users\Pratt\workspace\moodle-HEAD\lib\tablelib.php on line 362

Notice: Indirect modification of overloaded property moodle_session::$flextable has no effect in C:\Users\Pratt\workspace\moodle-HEAD\lib\tablelib.php on line 363

Notice: Indirect modification of overloaded property moodle_session::$flextable has no effect in C:\Users\Pratt\workspace\moodle-HEAD\lib\tablelib.php on line 364

Notice: Indirect modification of overloaded property moodle_session::$flextable has no effect in C:\Users\Pratt\workspace\moodle-HEAD\lib\tablelib.php on line 365

Notice: Indirect modification of overloaded property moodle_session::$flextable has no effect in C:\Users\Pratt\workspace\moodle-HEAD\lib\tablelib.php on line 368

Warning: Attempt to assign property of non-object in C:\Users\Pratt\workspace\moodle-HEAD\lib\tablelib.php on line 417

this is caused by http://bugs.php.net/bug.php?id=39449, grrrrrrrrrr

working on a hack

I hope this problem is now fixed in cvs

+1 for this, here at SFSU we running a really big site on a VM system (VMWare), and we are seeing some session-related issues that lead to slow performance....

db sessions are now working fine for mysql and pg, not compatible with mssql and oracle

As part of the change under this bug number, the following code was added:

} else if ((!isset($CFG->dbsessions) or $CFG->dbsessions) and $DB->session_lock_supported())

else {
// legacy limited file based storage - some features and auth plugins will not work, sorry
$session = new legacy_file_session();

For performance we were thinking about moving to local disk-based sessions and it would definitely be nice to have this as an option! Questions:

1) why do file sessions not work? do they really not work? is this documented somewhere as to what doesn't work? If so maybe the comment could include a link to the more detailed information. There is no info on legacy_file_session class either...

2) this is at the least unfortunate, when file sessions are a good way to take load off overworked db server...

(ok #2 that wasn't a question)

1/ file based sessions are problematic because you are not notified when the sessions expires - the file just gets deleted at some random time
2/ it is not possible to "query" folder with file sessions
3/ there are other way to off load db servers, for example shared memory

thanks.

#1 why/in which places does moodle need to know when the session expires, i.e. what does this break?

#2 why/in which places is the 'query' feature needed? This sounds like a dealbreaker for local file sessions as by definition it is not possible if they are stored locally and you have more than one server, however I don't understand why it would ever be necessary.

#3 I thought sessions were written on every request? if this is the case then they will still cause very high DB load even if the reads are cached.