Hi Anthony -

I'm sorry, I don't know the answer to your question, but the first thing I would do would be enable perf db. You've obviously enabled perf in general if you're seeing performance things in the footer, the perf db setting means that db queries are also counted.

Once you've done that, it should be easy to either blame or rule out excessive db queries

Hi Anthony,

I suspect it is probably an issue with the database. Have you checked your slow queries log? Are you logging slow queries?

I just realized that I hadn't posted a bug about this.

The following applies to a 1.5.4 system. We did some database level upgrades a few weeks ago that resulted in some impressive changes in load average as well as the amount of queries showing up via mysql_slow_queries.

For the assignment module the following is what we did;

ALTER TABLE `mdl_assignment_submissions` ADD INDEX `userid` (`userid`); 

ALTER TABLE `mdl_assignment_submissions` ADD INDEX `timemarked` (`timemarked`); 

ALTER TABLE `mdl_assignment_submissions` ADD INDEX `timemodified` (`timemodified`); 

ALTER TABLE `mdl_assignment_submissions` ADD INDEX `assignment` (`assignment`);

These commands will lock the assignment_submissions table so keep that in mind, and as always you should make a backup of your data first.

There were other index adds we did for other tables;

The log indexes will bar anyone from using the the site as this locks the log table while it is adding the index.

ALTER TABLE `mdl_log` ADD INDEX `userid` (`userid`); 

ALTER TABLE `mdl_log` ADD INDEX `module` (`module`); 

ALTER TABLE `mdl_log` ADD INDEX `action` (`action`); 

ALTER TABLE `mdl_log` ADD INDEX `info` (`info`); 

ALTER TABLE `mdl_log` ADD INDEX `time` (`time`);

If you are using db_sessions the following is critical

ALTER TABLE mdl_sessions CHANGE sesskey sesskey varchar(32) binary NOT NULL default '';

The query on db_sessions does a binary comparison (case-sensitive), but has an inappropriate index that can't be used. I wasn't sure that changing the query would be okay as adodb does a binary query on sessions so to be safe I adjusted the field to be appropriate for the query.

Added these as bugs;
MDL-7577
MDL-7578
MDL-7579