[OSM-dev] 404 from Apache2/mod_tile

[Kai Krueger]

Stefan Elspaß wrote
> Hi Kai,
> 
>> If I read your renderd log correctly, mod_tile is sending rendering
>> requests
>> with priority "dirty" rather than the "missing" priority. The dirty
>> priority
>> is a background priority in which mod_tile does not wait for the result
>> and
>> immediately returns the tile (or in case of a missing tile a 404).
> 
> This is indeed the case, but sometimes - in these seldom cases when
> rendering on the first request works - the "command RenderPrio" instead of
> "command Dirty" appears in /var/log/syslog (see below). Does that indicate
> that it might by a load-related decision from mod_tile?
> 
>> So the question is why does mod_tile send the requests with the incorrect
>> priority? This should only happen if the load average is above the
>> configured max missing load. Your configurations do look fine though.
> 
> Do you know by chance what unit "ModTileMaxLoadMissing" uses? Is it a
> percentage? The settings for the log below were as follows:

The load is in units of "number of processes that are wanting CPU time". It
is the load number you get from /proc/loadavg. So if you have a load average
of 500 on a 1 core system, then each process only gets 1/500th of a CPU and
will be dog slow. The load numbers should therefor typically be not too much
more than the number of CPU cores you have. Therefore unless something is
drastically wrong with your server, you really shouldn't be seeing a load of
500. 


Stefan Elspaß wrote
>> Can you increase the debug level of mod_tile to debug and then post your
>> apache error.log again? The debug output unfortunately currently doesn't
>> tell you what mod_tile thinks the load on the server is, but at least it
>> would confirm if this is the cause and what the configuration is set to.
> 
> In /etc/apache2/site-available/default I changed the log-value by changing
> the line to "LogLevel debug". Is there any other way to increase the debug
> level of mod_tile?

No, that is the correct way to increase the debug level of apache. And
setting it to debug, will include all of the other levels like info warning
and error.
However, apache does not log to syslog. It has its own error.log file. It
can typically be found in /var/log/apache/error.log

Kai



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