[Tilecache] Locking mechanism when generating new tiles?

[Ivan Mincik]

On Wednesday 10 February 2010, Russell McOrmond wrote:
>    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.

Hi, which TileCache version do You use ? There is a bug when using Metatiles which can be the case. (Patch r391 from 
SVN - broken locking when creating metaTiles)

-- 
Ivan 
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