public boolean isDeleteInvalidSessions() {
        return deleteInvalidSessions;
    }
Returns {@code true} if sessions should be automatically deleted after they are discovered to be invalid,
{@code false} if invalid sessions will be manually deleted by some process external to Shiro's control.  The
default is {@code true} to ensure no orphans exist in the underlying data store.
<h4>Usage</h4>
It is ok to set this to {@code false} <b><em>ONLY</em></b> if you have some other process that you manage yourself
that periodically deletes invalid sessions from the backing data store over time, such as via a Quartz or Cron
job.  If you do not do this, the invalid sessions will become 'orphans' and fill up the data store over time.
<p/>
This property is provided because some systems need the ability to perform querying/reporting against sessions in
the data store, even after they have stopped or expired.  Setting this attribute to {@code false} will allow
such querying, but with the caveat that the application developer/configurer deletes the sessions themselves by
some other means (cron, quartz, etc.).

@return {@code true} if sessions should be automatically deleted after they are discovered to be invalid,
{@code false} if invalid sessions will be manually deleted by some process external to Shiro's control.
@since 1.0
core/src/main/java/org/apache/shiro/session/mgt/DefaultSessionManager.java