Currently Crowd performs some writes in the database when a user authenticates. In particular, it always updates the lastAuthenticated user attribute (in com.atlassian.crowd.directory.DbCachingRemoteDirectory#performAuthenticationAndUpdateAttributes and com.atlassian.crowd.manager.authentication.TokenAuthenticationManagerImpl#updateUserLastActivity).

If a user authenticates with high frequency (e.g., via a REST API), that induces high write load in the database, typically to update a timestamp just by a few milliseconds.

As an optimisation, Crowd could avoid those writes in case the old and the new timestamps are close enough (let's say 1 minute), as it already does for the token last-access time (see parameter lastAccessedTimeUpdateThresholdMillis in com.atlassian.crowd.dao.token.TokenDAOHibernate#update).