[MapProxy] FYI: Possible root cause of 'sqlite3.OperationalError: database is locked'

Just van den Broecke just at justobjects.nl
Sun Mar 15 10:17:35 PDT 2015

Oops, forget my last mail: also observed on Ubuntu 14.04 :-(.
(my reseed yaml config was still seeding a file cache).

The package sqlite3 seems not to be involved. I can even uninstall the 
package. The library /usr/lib/x86_64-linux-gnu/libsqlite3.so.0.8.6 
provided by package libsqlite3-0 seems to be used from within Python.
Digging further....



On 15-03-15 17:07, Just van den Broecke wrote:
> Hi,
> I confirm this behaviour for MapProxy 1.7.1 on Ubuntu (with UbuntuGIS
> unstable PPA) using the standard Ubuntu package for sqlite3:
> - on Ubuntu 13.10 with "sqlite3 amd64 3.7.17-1ubuntu1", the
> 'sqlite3.OperationalError: database is locked'-error appeared.
> - after upgrading to Ubuntu 14.04.2 with "sqlite3 amd64 3.8.2-1ubuntu2",
> the error no longer occurred.
> Though the issue itself seems not to be version-dependent, but on the
> compiler-directive HAVE_USLEEP (which must be 1). So that flag may have
> been set for Ubuntu 14.04, which is as a better choice (LTS) anyway.
> Maybe of use for reproducing via e.g. Vagrant.
> best,
> Just
> On 10-01-15 18:36, Oliver Tonnhofer wrote:
>> Hi,
>> a few users reported 'sqlite3.OperationalError: database is locked’
>> during seeding or moderate load when using SQLite or MBTiles backends.
>> I could never reproduce and debug this on my systems, but I think that
>> I found the root cause.
>> On some systems SQLite is not compiled with USLEEP support. Without
>> USLEEP, SQLite will sleep a whole second every time another
>> thread/process is reading or writing to the same SQLite database.
>> Here is a detailed description of the issue:
>> http://beets.radbox.org/blog/sqlite-nightmare.html
>> You should try to upgrade your system or the SQLite version used by
>> Python if you see these lock errors.
>> Regards,
>> Oliver
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