[Akonadi] [Bug 338571] Performance Regression: Folder synchronisation in Akonadi 16.08 (actually in any release, starting with KDE 4.14) very slow, compared to kMail from KDE 4.13.x

[Gunter Ohrner via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=338571

--- Comment #24 from Gunter Ohrner <kdebugs at CustomCDROM.de> ---
I'm using regular IMAP but with a local IMAP server. Don't ask me why I'm doing
it this way, but apparently it's a good setup to detect performance bottlenecks
in the IMAP codepaths. ;)

Laurent Montel already assigned this report to "IMAP Resource" nearly two years
ago, so if he was right, you'll probably not be able to reproduce it with a
local Maildir resource. However if a Maildir resource scales much better, this
would be an indication that it's actually a "suboptimal behaviour" (i.e. "bug"
;) of the IMAP Resource and not "simply unavoidable" if you use Akonadi.

If I open a folder, the list of mails is basically shown immediately - but I
cannot display mails. One or two previously cached mails might display, but as
soon as I select an uncached mail, all mails become inaccessible until the
"Syncing folder 'ABCD'" operation finishes, which takes close to a minute to
complete and in most cases is executed twice before the folder becomes
operational. (Thus the 90 seconds delay during which the folder is not usable
and which happens every time I open the folder.)

That's how I temporarily enabled the query log:

- connect to the MySQL server using the mysql monitor (MariaDB will probably
work the same)
- SET GLOBAL log_output = "FILE";
- SET GLOBAL general_log_file = "/var/tmp/querylog.sql";
- SET GLOBAL general_log = 'ON';

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