[Interest] Qt 5.1.1 SQLite blocks database

[Martin]

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?

Thanks a lot!
Martin
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