In case it takes a while to process the reports for roll-ups, we recommend to setup Auto-Archiving. This is actually something we highly recommend for most Matomo (Piwik) installations as your reports will load much faster afterwards.
Depending on how often you decide to run the cronjob to archive the reports, we recommend to also adjust the time before an archive is considered outdated. If you for example run a cronjob every hour (every 3600 seconds), we recommend to set the outdated time to about 2700 seconds (45 minutes) in your
config/config.ini.php file like this:
[General] time_before_today_archive_considered_outdated = 2700 time_before_week_archive_considered_outdated = 2700 time_before_month_archive_considered_outdated = 2700 time_before_year_archive_considered_outdated = 2700 time_before_range_archive_considered_outdated = 2700
You could also set it to about 3500 seconds (about 58 minutes) but sometimes archives may be processed faster and sometimes they take a bit longer. Therefore 45 minutes (or 2700 seconds) may be a good value to ensure they will be re-archived with every cronjob execution.
Setting these values can improve the archiving of your roll-ups and prevent unneeded re-archiving of individual websites.