Performance cherry picks

[matthewhilton]

Background

• Client discovered emailing task is running out of memory
• Upstream codebase https://github.com/mdjnelson/moodle-mod_customcert has a few performance fixes here that we want, namely:
  • Number of certificates per run (instead of all)
  • Splitting emailing into an adhoc task
• we don't want this to cause an outage, so we cannot touch the db dir - this unfortunately means we cannot directly cherry pick from Mark's repo as the commits aren't clean and some touch the db dir.

Note, this is intended to be a temporary patch until the client moves off this fork (soon!)

Process

• First, I reverted PeterB's email performance fixes, as they are no longer necessary / superseded by these new improvements.
• Then I went to the MOODLE_500_STABLE branch and copied the 2 tasks + unit test for them and pasted them in here
  • Note I purposely used the latest branch as it has some bugfixes that the MOODLE_401_STABLE branch didn't have.
• I then renamed issue_certificates_task -> email_certificate_task (to allow db/tasks.php to be the same) and renamed email_certificate_task -> email_certificate_adhoc_task
• I renamed references to these in the tests + codebase
• Copied the necessary admin settings and lang strings
• Changed \core\cron::set_user() -> $this->set_userid (5.0 vs 4.1 API difference)
• Discovered 1 bug where adhoc tasks are not de-duplicated - so I added checkforexisting=true to the adhoc task queueing.
• Minor bumped the version (due to new lang strings)

Risks

• This should be fairly safe, the only risk would be if any other class changed and I did not copy those changes, however, from inspecting it I am fairly certain the only relevant changes are inside these two task classes

Testing

• Unit tests - passing
• Local testing - emailing works, task are de-duplicated as expected.

[rhell4]

Everything looks good to me, there are unit tests that cover the change and everything is green.