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  1. Moodle
  2. MDL-35088

Improve category enrolment performance in 2.2 (backport of MDL-34864)

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      On a large site with a significant number of category enrolled users, the following query will attempt to run multiple times over, eventually causing performance problems on the database.

      SELECT e.*, ue.userid
                    FROM mdl_enrol e
                    JOIN mdl_context ctx ON (ctx.instanceid = e.courseid AND ctx.contextlevel = '50')
                    JOIN mdl_user_enrolments ue ON (ue.enrolid = e.id)
               LEFT JOIN (SELECT DISTINCT cctx.path, ra.userid
                            FROM mdl_course_categories cc
                            JOIN mdl_context cctx ON (cctx.instanceid = cc.id AND cctx.contextlevel = '40')
                            JOIN mdl_role_assignments ra ON (ra.contextid = cctx.id AND ra.roleid IN ('5','9','11'))
                         ) cat ON (ctx.path LIKE CONCAT(cat.path, '/%') AND cat.userid = ue.userid)
                   WHERE e.enrol = 'category' AND cat.userid IS NULL

      Please optimize this query.

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              skodak Petr Skoda
              mchurch Mike Churchward
              David Woloszyn, Huong Nguyen, Jake Dallimore, Michael Hawkins, Stevani Andolo
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