preg_match(): Compilation failed: regular expression is too large

Hello, I also get this error !

I didn't have it before updrading to codeigniter3.
The workaround I found (end of post) is temporary and you don't want to leave it like that, it is a security breach.

My usecase is a BIG where_in with tousands IDs. Increasing temporarly the ini value does not work.
What should I do ?

Sincerely 
Nicolas

PHP Code:

if (strlen($conditions[$ci]) > 10000) {
//                        ini_set("pcre.backtrack_limit", 100000000000);
//                        ini_set("pcre.recursion_limit", 10000000000);
                        continue;
                    } else {
                        if (
                            ( $op = $this->_get_operator( $conditions[ $ci ] ) ) === false
                            OR ! preg_match( '/^(\(?)(.*)(' . preg_quote( $op, '/' ) . ')\s*(.*(?<!\)))?(\)?)$/i', $conditions[ $ci ], $matches )
                        ) {
                            continue;
                        }
                    }