[Akonadi] [Bug 334209] New: synchronizes folder contents with filesystem on switching folders needlessly

[Martin Steigerwald]

https://bugs.kde.org/show_bug.cgi?id=334209

            Bug ID: 334209
           Summary: synchronizes folder contents with filesystem on
                    switching folders needlessly
    Classification: Unclassified
           Product: Akonadi
           Version: GIT (master)
          Platform: unspecified
                OS: Linux
            Status: UNCONFIRMED
          Severity: normal
          Priority: NOR
         Component: Maildir Resource
          Assignee: kdepim-bugs at kde.org
          Reporter: Martin at Lichtvoll.de

I think Akonadi synchronrizes folders with filesystem content needlessly on
switching between different folders. In combination with bug 334206 it blocks
out KMail for minutes then.

Reproducible: Always

Steps to Reproduce:
1. Have several large folders.
2. Switch between them until Akonadi blocks KMail and KMail doesn´t respond to
clicks anymore.
Actual Results:  
1. KMail doesn´t respond to clicks anymore for minutes.
2. akonadi_maildir_resource is using 100% of one Sandybridge core for minutes.
3. strace reveals that akonadi_maildir_resource is stat()ing every single file
in the folder it synchronrizes.

[pid  4137]
stat("/home/martin/.local/share/local-mail/.Lichtvoll.directory/.Linux.directory/kernel-ml/new/1376733031.R234.merkaba",
{st_mode=S_IFREG|0644, st_size=4079, ...}) = 0
[pid  4137]
stat("/home/martin/.local/share/local-mail/.Lichtvoll.directory/.Linux.directory/kernel-ml/new/1376733031.R322.merkaba",
{st_mode=S_IFREG|0644, st_size=8056, ...}) = 0
[pid  4137]
stat("/home/martin/.local/share/local-mail/.Lichtvoll.directory/.Linux.directory/kernel-ml/new/1376733031.R342.merkaba",
{st_mode=S_IFREG|0644, st_size=2771, ...}) = 0
[pid  4137]
stat("/home/martin/.local/share/local-mail/.Lichtvoll.directory/.Linux.directory/kernel-ml/new/1376733031.R608.merkaba",
{st_mode=S_IFREG|0644, st_size=4492, ...}) = 0
[pid  4137]
stat("/home/martin/.local/share/local-mail/.Lichtvoll.directory/.Linux.directory/kernel-ml/new/1376733031.R665.merkaba",
{st_mode=S_IFREG|0644, st_size=13036, ...}) = 0
[pid  4137]
stat("/home/martin/.local/share/local-mail/.Lichtvoll.directory/.Linux.directory/kernel-ml/new/1376733031.R738.merkaba",
^C{st_mode=S_IFREG|0644, st_size=6870, ...}) = 0

This doens´t happen all of the time tough. Sometimes I am able to click around
folders without having this issue. I am able to reproduce this directly after
restarting Akonadi. There synchronizing folders for *one* time actually makes
sense as a folder may have been changed meanwhile by another process. An option
to disable this if user knows that no one except Akonadi will be accessing this
maildir would be nice tough.

I think it doesn´t happen only after restart tough. Usually I have Akonadi
running for days as I hibernate and resume my laptop. And I see this behaviour
each day. IMHO there does not need any folder with filesystem contents
synchronisation during runtime of Akonadi as maildir resource uses inotify to
watch folders.

Expected Results:  
There will be no synchronisation with filesystem contents during runtime of
Akonadi as Akonadi maildir resource uses inotify to watch the folders for
changes.

ThinkPad T520 with Sandybridge Dual core and Dual SSD BTRFS RAID 1. There is
*no* I/O bottleneck. Maildir resource just hogs a core for minutes.

Akonadi is git n1d1969c65c10c9d3f054f6dafb0f5a2a97d48281

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