After migrating an old KMail installation to Akonadi-based KMail 2, Akonadi spins with high CPU load, spamming lines like akonadi_maildispatcher_agent(3812)/libakonadi: Resource id's don't match: "akonadi_mixedmaildir_resource_0" "akonadi_maildir_resource_0" to the xsession-errors. In this state, KMail also seems to become inconsistent with IMAP accounts, meaning that deleting, moving, copying messages lead to the client showing things that are in no way reflecting what was done on the server. "Moved" messages turn out to be duplicated, and I don't even want to know if it always greps the right ones. This appears to be a long-standing issue, and it IMO means that KMail should not be used since the desync means users are likely to lose data at some point. There is also no way for a "normal" user to track down and diagnose that issue. I propose that migration is completely disabled by default and users be told to erase their configuration and start new, which appears to have a 50% chance of working.
I can confirm this issue and this is quite sever as now akonadi and mysql are collectively eating a whole CPU and I have no idea how to solve the issue.
It looks like there's a problem that the migration code has created "Local Folders" as a mixedmaildir resource, but we expect it to be a maildir resource (maildir is used by default in newly created Akonadi). Open Akonadi Console and check whether you have "Local Folders" resource twice and remove the one of the type "akonadi_maildir_resource_0", then restart Akonadi.
There is related debian bug report https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=727800 that appears to be the same issue.
Git commit 020cfb32f7a2c4ae57b0cda20e97dbc0acb38785 by Diane Trout. Committed on 21/01/2015 at 18:39. Pushed by dtrout into branch 'KDE/4.14'. Restart akonadi when we finish migration. This helps with the infinite loop because of resource ids don't match reported in kde bug 322471 and debian bug 727800. REVIEW: 122187 M +4 -0 migration/kmail/kmailmigrator.cpp http://commits.kde.org/kdepim-runtime/020cfb32f7a2c4ae57b0cda20e97dbc0acb38785
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.
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.