[Akonadi] [Bug 336582] New: Sudden write interruption during akonadictl vacuum causes database corruption

[Martin Steigerwald]

https://bugs.kde.org/show_bug.cgi?id=336582

            Bug ID: 336582
           Summary: Sudden write interruption during akonadictl vacuum
                    causes database corruption
    Classification: Unclassified
           Product: Akonadi
           Version: GIT (master)
          Platform: Compiled Sources
                OS: Linux
            Status: UNCONFIRMED
          Severity: critical
          Priority: NOR
         Component: general
          Assignee: kdepim-bugs at kde.org
          Reporter: Martin at Lichtvoll.de

As Akonadi despite my changes to stop sorting of filenames in Maildir resources
got slower and slower again, I thought I try akonadictl vacuum. I had a kernel
compile running at that time and well… as it sometimes happens during heavy I/O
BTRFS seemed to lock up. Thus I rebooted.

On reboot the Akonadi database was corrupted. parttable.ibd and another file
was zero byte long.

Reproducible: Didn't try

Steps to Reproduce:
1. Run akonadictl vacuum
2. Switch off the machine
3. Restart
Actual Results:  
Database corrupted. Some files are zero byte.

Expected Results:  
Database is intact.

Why do I think this is a bug?

Even with delayed allocation, if an application does proper renaming and
fsync() the file is either renamed and written or not. I consider a cache for
pim data important. And thus it has to use fsync(). This may well be something
in MySQL at play here.

Together with

Bug 336581 New: accidental database loss causes Akonadi / KMail breaks correct
folder assignments

its even more important to never ever loose the database.

Potential culprits in default mysql.conf for Akonadi:

# Write out the log buffer to the log file at each commit (default:1)
innodb_flush_log_at_trx_commit=2

And if default is 0:

#sync_bin_log=0

Would be nice to have extra bugzilla entries for different DB backends.

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