Missing logstore_standard index significantly slows backups with logs

The performance implication for this is hard to test, since it requires very large logstore_standard_log tables (for reference, ours is ~145M records), and courses with logs of activities with logs. Because of this, we basically want to make sure we didn't break anything: Start before applying the patch. Create a course with a number of resources (like Page). You can just use a Small test course. As both a teacher and a student, navigate around the course and into pages. The goal here is just to make log records. Backup the course, making sure to include course logs. Apply this patch Backup the course again, again making sure the course logs are enabled. Download and extract both back files. Recursively diff the two resulting folders Compare them, there should only be trivial differences between them. Some additional testing steps: Do a clean install with this patch, examine the DB and ensure the index on the contextid field in the logstore_standard_log table was created. Do an upgrade from a previous version, examine the DB and ensure the index on the contextid field in the logstore_standard_log table was created. On a pre-upgrade site, manually add the index on contextid, then upgrade the site and make sure there are no errors.