[kmail2] [Bug 331848] New: displaying, moving, deleting mails takes 10-20 seconds when Akonadi synchronizes in background

[Martin Steigerwald]

https://bugs.kde.org/show_bug.cgi?id=331848

            Bug ID: 331848
           Summary: displaying, moving, deleting mails takes 10-20 seconds
                     when Akonadi synchronizes in background
    Classification: Unclassified
           Product: kmail2
           Version: 4.12.2
          Platform: Debian unstable
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: message list
          Assignee: kdepim-bugs at kde.org
          Reporter: ms at teamix.de

This is no duplicate of

Bug 327017 - Message takes over 1 minute or 2 to show up due to Kmail syncing
folders. 

as I checked in Akonadiconsole that there are no duplicate folders for Local
Folders.

This is with a clustered Exchange server. I also tested with Icedove 23.1 and
there switching between mails in a folder is almost instant.



Reproducible: Sometimes

Steps to Reproduce:
1. Have large IMAP account (I think it doesn´t matter if its on Exchange or
not, but I am not sure).
2. Access a folder with quite some mails (I tested with btrfs-ml which has
about 13500 unread mails).
3. Switch between mails by clicking on them or with cursor keys.

Actual Results:  
Displaying the mail takes 10-20 seconds during which "Receiving folder contents
is displayed" (translated from german).

Expected Results:  
The mail is displayed almost instantly (as long as the IMAP server does respond
in time). It does so while there Akonadi does not synchronize folders here.

I use the following workaround: Cause synchronizing through the huge lot of the
mail folders takes quite long, I raised regular sync interval from 15 to 30
minutes. So at least during some time I have faster access times.

I think I remember having read once that Akonadi is at some point
single-threaded, i.e. can only do one task at a time. If this is the case I
think it should at least pause any background tasks *immediately* on user
input. Better yet, I think, is to support more than one task being processed at
a time and supporting some kind of priority in scheduling them, so that
background tasks can be set to lower priority.

Currently this is a major issue in usability of KMail. I revert to Outlook Web
Access or Icedove in case KMail is unresponsive, which with 15 minutes sync
interval was quite often. I as a user just don´t like to wait for Akonadi
getting to process my interactive request.

Its not only with displaying mails, but also moving some or deleting some. With
modifying operations it takes KMail even longer. Up to minutes. Also if KMail
synchronizes a large folder it takes longer as well for it to respond even to
requests to display a mail.

Here this is with IMAP. I also see it on POP3 accounts with deleting mails
directly after having told it to get receive new mails to me and sometimes also
on other occastions.

Maybe this just happens with really large mailboxes with lots of folders and up
to tens of thousands of mails in some of them. For the IMAP account I already
disabled subscription of linux-kernel-ml folder due to having more than 400000
unread mails in them.

Still there is a MySQL database, and all Akonadi has to do is request the item
I clicked on from the IMAP server. IMHO its not supposed to take that long and
IMHO it has to do with internal scheduling in Akonadi.

This is on a ThinkPad T520 with Sandybridge 2,5 GHz Dualcore and dual SSD BTRFS
RAID 1. So the machine is really quite fast. The Exchange cluster is hosted
within our ESX enviromnent and usually responds really fast in Outlook Web
Access and Icedove. I think it has quite fast backing hardware as well.

ms at merkaba:~> apt-show-versions | egrep "(kmail|akonadi)"
akonadi-backend-mysql:all/sid 1.11.0-1 uptodate
akonadi-backend-sqlite:amd64/sid 1.11.0-1 uptodate
akonadi-server:amd64/sid 1.11.0-1 uptodate
akonadiconsole:amd64/experimental 4:4.12.3-1 uptodate
kmail:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-calendar4:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-contact4:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-dev:amd64/sid 1.11.0-1 uptodate
libakonadi-kabc4:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-kcal4:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-kde4:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-kmime4:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-notes4:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-socialutils4:amd64/experimental 4:4.12.3-1 uptodate
libakonadi-xml4:amd64/experimental 4:4.12.3-1 uptodate
libakonadiprotocolinternals1:amd64/sid 1.11.0-1 uptodate

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