The Job Tracker shows how Akonadi::SpecialMailCollectionsRequestJob are started and terminated continuously, causing mysqld and akonadi itself to use 50% of one of my cores, for doing absolutely nothing. I am unaware of the internal implementation details and I've just updated to kmail2 today, so I am pretty new, but since I had no outgoing emails I don't see the reason for all this activity. Reproducible: Always
+1 I'm also on Debian and on KDE 4.10.2 and also experienced this high CPU consumption after syncing my work mail (~65000 messages on an IMAP server). Meanwhile it did endless SELECT queries to mysql. Then I restarted Akonadi and it stopped eating my CPU. But KMail started eating it itself. It says "ready" but does something. WHAT DOES IT DO? For what purpose? Even OPERA MAIL works MUCH FASTER (!!!) Opera deals with my mail without problem, while KMail doesn't. Yet it improved over 4.8 - in 4.8 it also ate ALL available RAM...........
This bug has only been reported for versions older than KDEPIM 4.14 (at most akonadi-1.3). Can anyone tell if this bug still present? If noone confirms this bug for a recent version of akonadi (part of KDE Applications 15.08 or later), it gets closed in about three months.
I gave up on akonadi, I think it's beyond fixing and I moved on to a mail client that can receive and send mails. So, feel free to close all the bugs I opened because I won't be trying to reproduce them.
Just as announced in my last comment, I close this bug. If you encounter it again in a recent version (at least 5.0 aka 15.08), please open a new one unless it already exists. Thank you for all your input.