archived items waiting to be indexed

We're currently running EV 8.0 SP3.  I plan to upgrade to EV9.0.4 tonight

However, I've found that on particular mailbox index that has been in a continual rebuild and was wondering if that will have any effect with the upgrade planned for tonight.  Can or should I take it offline? 

Also, finding 116891 archived items that are waiting to be indexed.  Does this number need to be cleared before proceeding with upgrade? I thought this was relative to backups but it appears it may not be. 

Thanks for any information anyone can  provide.