Related issue: Slow load times as a result of getMailingsList()
Not a bug, but just to flag a related issue. I was trying to track down why 'Scheduled and Sent Mailings' and 'Draft and Unscheduled Mailings' were so slow to open. It turned out to be because of a call to CRM_Mailing_BAO_Mailing::getMailingsList().
This queries all existing mailings (archived or not). It left joins onto the mailing_job table to get the date the mailing finished. We have 15k mailings and almost 2m jobs(!), so this query took a while to complete - and was only going to ever get bigger.
My temporary fix was switching to the mailing scheduled_date and ditching the left join entirely - this reduces it to an entirely trivial query and sped up page loads by like 9 seconds.
(Ironically the two above pages don't even use the generated data - I think this is mainly used for the dropdown in Advanced Search)
But just thought you might like to know about this source of slow load times - that archiving doesn't help with.