[Akonadi] [Bug 389829] "Unable to fetch item from backend" after deleting it using akonadi_maildir_resource_0

[Raúl]

https://bugs.kde.org/show_bug.cgi?id=389829

--- Comment #14 from Raúl <rasasi78 at gmail.com> ---
Attila, sorry for the delay in answering. I'm not a KDE developer but I can
explain you what I suspect about this bug and how it can be related (if not
duped) to https://bugs.kde.org/show_bug.cgi?id=434706.

kontact/akonadi is a user fronted which shows data that those get from akonadi
which, in turn, is closely bounded to a database. The database is made up of
tables and registers. You can take a look at those tables and registers using
an external database browser or the database command line client. For instance,
in my case akonadi relies on mariadb database engine and I can query the
akonadi data externally like this:
```
$ mariadb -S/run/user/1001/akonadi/mysql.socket
MariaDB [(none)]> use akonadi;
MariaDB [akonadi]> show tables ;
+----------------------------------+
| Tables_in_akonadi                |
+----------------------------------+
| collectionattributetable         |
| collectionmimetyperelation       |
| collectionpimitemrelation        |
| collectiontable                  |
| flagtable                        |
| mimetypetable                    |
| parttable                        |
| parttypetable                    |
| pimitemflagrelation              |
| pimitemtable                     |
| pimitemtagrelation               |
| relationtable                    |
| relationtypetable                |
| resourcetable                    |
| schemaversiontable               |
| tagattributetable                |
| tagremoteidresourcerelationtable |
| tagtable                         |
| tagtypetable                     |
+----------------------------------+
19 rows in set (0.001 sec)
```

kontact/kmail sends database queries to feed akonadi database and also to
retrieve data. I think either the query flow or the database engine has some
kind of bug or limitation. Hence one of the database queries locks some
database tables (like those listed above) and therefore most of the database
operations are locked (they cannot be completed).

https://bugs.kde.org/show_bug.cgi?id=434706 explains some similar behavior and
that is why I asked you to check if both reports are about the same problem.
You are right that https://bugs.kde.org/show_bug.cgi?id=434706 is too technical
and this is where you could get lost.

In order to check whether the problem is the same or not, here is the list of
actions that you can perform to verify:
* Wait for the problem to reproduce or reproduce it yourself (if possible)
* Check `journalctl -xe` output and look for recent  output like this:
```
kmail[1317]: org.kde.pim.akonadicore: Received response with a different tag!
akonadi_maildispatcher_agent[1586]: void SendJob::setFrom(const QString &from) 
"mail at milianw.de"
akonadi_maildispatcher_agent[1586]: d->m_returnPath   "<mail at milianw.de>"
akonadiserver[1305]: org.kde.pim.akonadiserver: QueryBuilder::exec(): database
reported transaction deadlock, retrying transaction
akonadiserver[1305]: org.kde.pim.akonadiserver: "Deadlock found when trying to
get lock; try restarting transaction QMYSQL3: Unable to execute statement"
akonadi_imap_resource[1583]: org.kde.pim.imapresource: "Connection to server
lost."
```
* Additionally you can connect to the mariadb socket: `mariadb
-S/run/user/1001/akonadi/mysql.socket` (1001 is your user code, maybe it's a
different number)
* Issue the following db engine query: `SHOW ENGINE INNODB STATUS` you should
see that there is a deadlock detected: *LATEST DETECTED DEADLOCK* section in
the https://bugs.kde.org/show_bug.cgi?id=434706 bug

If you find out the same outcome, this and the other bug are quite possibly a
duplicated.

One additional comment is that I think the bug is not specifically about kmail,
but about akonadi and its database engine usage.

For getting a fix, we would need that someone with enough akonadi and DB
knowledge to analyze and find out possible solutions. Unfortunately that is not
by my hand.

Regards,

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