Large filter subscriptions can crash a JIRA instance with an OutOfMemoryError

Summary

JIRA has no 'rate limiting' or mail limit on filter subscriptions. This means using certain configurations will allow for a significant amount of mail to be created. As this mail is persisted in memory, it's possible to cause OutOfMemoryError's, even with a significant amount of heap space.

Steps to Reproduce

1. Use an instance with a large amount of issues and users, using test mail addresses.
2. Enable mail notifications.
3. Setup a filter subscription that will notify all users (for example sends to jira-users), using JQL as below:

   updated < "-200m"
   

4. Set a high frequency on the updates as per the screenshot.

Expected Results

Some form of rate limiting, or logic is used such that the instance does not result in consuming all of the available heap space and crashing with an OutOfMemoryError.

Actual Results

An OutOfMemoryError is thrown as the heap space fills up with mails.

Workaround

Avoid using filter subscriptions with large recipient bases that use a filter that returns a large amount of issues.
SQLs to check that:

// Check subscription
select * from filtersubscription;

// check JQL for subscription
select s.id, s.reqcontent, s.filtername, s.authorname, fs.groupname from filtersubscription fs 
join searchrequest s ON fs.filter_i_d = s.id;

// Check large groups subscription
select * from filtersubscription where groupname in (select parent_name from cwd_membership where membership_type = 'GROUP_USER' group by parent_name, directory_id having count(1) > 100);