[Interest] Qt 5.1.1 SQLite blocks database

[Constantin Makshin]

Obviously, that would mean losing all benefits of QtSql in the form of a
RDBMS-neutral API and, as a consequence, [relatively] easy migration
between backends.

To Martin:
Are you sure the problem is caused by changes in Qt and not SQLite?
Comparing "src/sql/drivers/sqlite/qsql_sqlite.cpp" on Gitorious shows
that the QSQLiteDriver::open() method is pretty much the same in Qt4.8
and Qt5 — in Qt5 it has Q_D() and somewhat better error handling,
nothing more.

On 10/30/2013 04:51 PM, Konstantin Tokarev wrote:
> 30.10.2013, 11:46, "Martin" <freebsd at rakor-net.de>:
>> Hi there!
>>
>> I have a project written in Qt4.8 using the bundeled SQLite (Version 3.7.14.1). This program is running on multiple machines sharing the same sqlite-database. The program is for informational purposes and therefore with very few writing-access. This worked without issues all the time. (I know that it is not recommended to use a sqlite-file over a network-connection, but I need this).
>>
>> Now I am porting to Qt 5.1.1 and also using the bundeled SQLite (Version 3.7.17). The program runs without flaws, but as I start a second client it can not make any changes to the database getting the error “database is locked Unable to fetch row". It seems to me, that the first program using the database sets a database-wide lock until it is closed. So the first program opening the database has full access. Any program opening the database to a later point of time has only read-permissins.
>>
>> I tried to set the locking-mode PRAGMA to Normal (I know it should be at normal anyway).
>>
>> The problem remains when I use multiple clients on the same machine, using a local database-file (so it has nothing to do with network-filesystems locking features).
>>
>> I have started a thead on the forum https://qt-project.org/forums/viewthread/34130/#148660 and there I got the advice to send an email to this list.
>>
>> Asking in the sqlite-mailinglist I got this reply:
>>> Sounds like something changed in Qt 5.1.1 so that it is holding open a read
>>> transaction. The first process acquires the read transaction, which
>>> permits other processes to read but prevents anybody else from writing. I
>>> have no idea why Qt would do this, though.
>>> […]
>>> I think your goal should be to figure out why Qt 5.1.1 is holding open the
>>> read transaction.
>>
>> So could you help with this issue? Was there any change in the way Qt handels SQLite-Databases? Could I somehow avoid this?
> 
> You can use SQLite directly instead of relying on QtSql with SQLite plugin.

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