[Tilecache] Locking mechanism when generating new tiles?

[Russell McOrmond]

   I'm curious what Tilecache does for locking when generating a new tile? 
If multiple clients request the same tile that isn't yet in the cache, 
what happens?   Do both Tilecache instances request the tile from 
Mapserver?


   The reason I'm asking is we are having a very intermittant problem that 
locks up our server.   We have separate virtual machines for TileCache, 
Mapserver, and other components.   On Tilecache we observe a scenario 
where all of a sudden requests start to wait and new ones build up until 
resources get used up (many waiting Apache processes).  There isn't any 
significant CPU usage, just lots of ram used up from waiting Apache 
processes.

   The only thing that came to my mind was some sort of race condition.


   We don't yet have a way to reliably replicate the issue, and it only 
happens periodically, so don't have anything specific to report yet -- 
only investigating possibilities.

-- 
  Russell McOrmond, Internet Consultant: <http://www.flora.ca/>
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