mapnik (OGR) fails silently giving an empty tile in case of network outage and/or SQL server is unreachable

[saurabhpandit]

I am having problem with OGR plugin. mapnik.load_map is a blocking statement and it throws error if SQL server is unreachable but where as mapnik.render fails silently
so I get an empty tile instead of some sort of exception
any idea how I can make sure that either tile gets rendered properly or it throws an error

[springmeyer]

Hi @saurabhpandit - I'm not sure why the failure during rendering is silent. But I agree with you that it should not be silent. I suspect fixing this will requiring testing changes to the Mapnik OGR plugin. As a first step I would recommend building Mapnik in DEBUG mode and then seeing if this code is triggered: https://github.com/mapnik/mapnik/blob/master/plugins/input/ogr/ogr_layer_ptr.hpp#L171-L187. It may be that the OGR plugin needs to start checking more OGR error codes.

Let me know if that helps and you are able to rebuild Mapnik in Debug mode.

[saurabhpandit]

My mapnik is built with debug mode but it does not print any of the above debug statements.

[saurabhpandit]

But I can tell you that other debug statements are being printed.

[springmeyer]

@saurabhpandit - sorry, try passing ./configure ENABLE_LOG=True DEBUG=True

[saurabhpandit]

Yep. We have configured mapnik with ENABLE_LOG=True DEBUG=True since we compiled it first time.

[springmeyer]

Okay, then the issue is likely that you need to change the "severity" to get DEBUG level to show up. See https://github.com/mapnik/mapnik/wiki/Logging. The other quick workaround would be to do: https://gist.github.com/springmeyer/92386296c2f1addfa69c