[Tile-serving] [openstreetmap/mod_tile] Preventing mod_tile rendering from blocking the serving of cached tiles? (#182)

[Frederik Ramm]

What you describe must have another reason than you think.

When mod_tile finds a tile in the cache that is not old, it will deliver the tile without even talking to renderd, i.e. mod_tile at that point wouldn't even *know* whether renderd is under load or not. 

You could be seeing congestion on the Apache side (depending on which MPM you have and how it is configured) - try to request a harmless static page, does that work?

Or you could be seeing disk congestion so bad that mod_tile cannot even access the meta tile and extract the PNG from it. (unlikely!)

Or, you might have an old tile in the cache, and depending on the `ModTileRequestTimeout` setting, mod_tile might try to have the old tile rendered before handing out an old one. This would, however, not mean that old tiles are never delivered - they would be delievered after `ModTileRequestTimeout` seconds.


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