Calculating the values of AuthorOfLastUpdateOrComment and Participants custom fields takes a long time to complete

Issue Summary

Jira Toolkit, a popular Atlassian Labs plugin contains two custom fields, AuthorOfLastUpdateOrComment and Participants. Calculation of values for these two fields has performance impact in cases when the issue has a lot of comments. The direct reason for that is that each processed comment causes a user lookup in Jira CommentSearchManager.java code.

Steps to Reproduce

1. Run any action that involves generation of JSON representation of the issue.

Expected Results

The amount of calls to user subsystem is equal to the amount of unique participants in the issue.

Actual Results

The amount of calls to user subsystem is more than twice bigger than the amount of comments on the issue.

Workaround

Currently there is no known workaround for this behavior.