Sites with large numbers of cohorts cannot load settings page, very poor performance

[matthewhilton]

Description

• When installed on a site with a large number of cohorts, the plugin does not efficiently query them in the plugin settings, leading to very poor performance.
• Performance issues are across most site administration pages since moodle tries to re-query the settings
• The site in question has 165,652 cohorts
• The actual xapi settings page tries to make a checkbox for each cohort. This takes ages to load each checkbox and is more or less unusable, and likely will crash browsers on lower spec machines

Version

• master at 416b92cfd672e02e1c92b5011ee6395bb95a5111 on 2022101800

Steps to reproduce the bug

1. Enable profiling via site administration
2. Create a large number of cohorts
3. Profile the admin search page https://site.com/admin/search.php?PROFILEME=1
4. Check profiling run. In this site, the profiling run shows the following trace taking a large chunk of time:

admin_get_root
core\plugininfo\tool::load_settings
tool_log\plugininfo\logstore::load_settings
logstore_xapi_get_cohorts

The logstore_xapi_get_cohorts step takes ~10 seconds of execution time.

Expected behaviour

• Plugin does not impact site performance unnecessarily

Actual behaviour

• Admin page takes > 10 minutes to load.
• It tries to make a checkbox for each cohort. If I let it run, it tries to make 100,000+ checkboxes.

Server information

• Postgresql
• Moodle 4.1
• OS: Linux

I would recommend using recordsets to get the data, and refactoring the settings page to use a search/autocomplete box with multi select option.