Without it, transactions are executed in standard READ_COMMITED
mode, without snapshoting/row versioning, leading to update
conflicts under high concurrency.
MSSQL's substring() implementation is somehow silly/strict and unable to
perform implicit casts to integer both for the start and length parameters.
This hits Moodle badly because of another problems (MDL-23997) we decided
to cast to string all bound placeholders long ago.
So this commit just enforces the cast of the start and length parameters to
integer. And includes unit tests for using placeholders on all positions in
the sql_substr() method.
Only MySQL is allowed to run Moodle instances without
(with an empty) database prefix. The rationale is that
"user" is a reserved word in every RDBMS but MySQL.
Before this patch, installation was breaking badly, when
the "user" CREATE TABLE statement was issued. With this
patch the error is shown earlier (on connection) preventing
any advance/use of the database.
This check is present in all the drivers, just sqlsrv was missing it.
When insert_record is called and it doesn't find any columns
to insert data into, that is a dml_exception as you need at least
one column in the database to insert into it. This can happen
when you have created a zero column database table, or the table
does not exist.
Includes following fixes:
* support for MS SQL Server
* optional trimming of of oversized VARCHAR fields
* conversion to forms library
* full localisation
* other cleanup
List of changes:
* New OOP API using PHP namespace \core\session\.
* All handlers now update the sessions table consistently.
* Experimental DB session support in Oracle.
* Full support for session file handler (filesystem locking required).
* New option for alternative session directory.
* Official memcached session handler support.
* Workaround for memcached version with non-functional gc.
* Improved security - forced session id regeneration.
* Improved compatibility with recent PHP releases.
* Fixed borked CSS during install in debug mode.
* Switched to file based sessions in new installs.
* DB session setting disappears if DB does not support sessions.
* DB session setting disappears if session handler specified in config.php.
* Fast purging of sessions used in request only.
* No legacy distinction - file, database and memcached support the same functionality.
* Session handler name included in performance info.
* Fixed user_loggedin and user_loggedout event triggering.
* Other minor bugfixing and improvements.
* Fixed database session segfault if MUC disposed before $DB.
Limitations:
* Session access time is now updated right after session start.
* Support for $CFG->sessionlockloggedinonly was removed.
* First request does not update userid in sessions table.
* The timeouts may break badly if server hosting forces PHP.ini session settings.
* The session GC is a lot slower, we do not rely on external session timeouts.
* There cannot be any hooks triggered at the session write time.
* File and memcached handlers do not support session lock acquire timeouts.
* Some low level PHP session functions can not be used directly in Moodle code.
Looping over large numbers of items with array_shift() is expensive.
Reverse the array and fetch items from the top of the pile.
Credit goes to Martin Langhoff for original mysqli fix.
