[OSM-Devserver] mod_tile/Tirex sometimes rendering checkered tiles

[Kay Drangmeister]

Hi.

I have a working setup with mod_tile + tirex/wms-backend + my_own_slow_wms_renderer

Sometimes, however, there are black/yellow checkered tiles like this one:
http://drangmeister.net/tmp/44568.png

The according metatile looks like this:
-rw-r--r--  1 tirex tirex    9108 2010-07-07 23:21 8.meta

i.e. is very short. About 70% of the metatiles are like this. This is although
my renderer produced a valid image (seen in the rendering temp dir). So I presume
this may be due to a timeout somewhere. I already set the following timeouts:

/etc/tirex/tirex.conf:

#  If the rendering of a metatile takes more than this many minutes the master
#  gives up on it and removes the job from the list of currently rendering tiles.
master_rendering_timeout=60
(one hour)
backend_manager_alive_timeout=57

/etc/tirex/renderer/wms/myrenderer.conf

- there is no timeout here. Correct?

/etc/apache2/conf.d/mod_tile.conf

# Timeout before giving up for a tile to be rendered
     ModTileRequestTimeout 300 [<- pretty sure this means minutes, please confirm]
# Timeout before giving up for a tile to be rendered that is otherwise missing
     ModTileMissingRequestTimeout 100
# If tile is out of date, don't re-render it if past this load threshold (users gets old tile)
     ModTileMaxLoadOld 2
# If tile is missing, don't render it if past this load threshold (user gets 404 error)
     ModTileMaxLoadMissing 5

No other timeout that I can think of.
My metatiles take about 3 to 5 minutes to generate.

Question: what part of my chain renders that checkered metatiles and why?

Thanks,
Kay