Recommended Updates email process runs for a long time consuming resources

Summary

When using a large instance of Confluence, the recommended updates email process may run for a long time while pulling large amounts of data from the database. This can sometimes cause an outage to Confluence as everything gets bottlenecked on this. This differs from CONF-30581 as that bug was caused by multiple concurrent running schedules, but this bug is caused by a single large schedule.

Steps to Reproduce

1. Have a very large instance of Confluence
2. Allow the recommended updates email process to run

Expected Results

No hit to performance

Actual Results

Confluence performs slowly and may even become totally unresponsive

Workaround

Disable the Daily Summary Email scheduled job as described at Configuring the recommended updates email notification