Active user count recalculates for every JIRA's inactive user during user synchronisation

Summary

When running LDAP synchronisation Crowd mechanisms are trying to remove every user in JIRA that is not present in LDAP. Removal won't happen because of fix for JRA-24937.

Expected Results

It won't recalculate when it detects deletion request for user that was deleted more than X minutes ago.

Actual Results

With each user delete event JIRA will clear user count cache.
When instance is under typical load we experience need of recalculation of user count each cache clear.

Problem

The issue can significantly increase JIRA's response times during user directory synchronisation. The efect is very noticable on instances with high number of inactive users.

Cause

Problem is caused by combination of multiple factors:

• JIRA leaves inactive users in user pool
• Crowd has no knowledge of "inactive users"
• Crowd throws user deletion event for every user separately
• JIRA checks for licence exceed with request and not by schedule
• On user delete JIRA needs to recalculate the user count again
• Directory sync is not atomic operation.
• Cache invalidation needs to wait for pending cache load to finish