Purging. Now what?

[Poul-Henning Kamp]

In message <20061114100441.GA24310 at crusaders.no>, Trond Michelsen writes:

>Well, since we're using tiled images, the number of potential URLs
>becomes quite large very fast. At any given zoomlevel, there are
>4**zoomlevel tiles. So at zoomlevel 12 (which we use for Google
>Earth), there are 16,7 million tiles. We have about 20 different
>datalayers, and every layer contains data for every hour for 48
>hours. That means that we have to purge up to 16 billion tiles when a
>datamodel is updated (about every 12 hours)[1]. Since our internal
>WMS-server is fairly slow, we really, really don't want to generate
>any tiles more than once, so it's important for us that Varnish keeps
>everything in cache until it's purged.

This is exactly what Varnish's url.purge facility is supposed
to help you do.  All that is required is that you can express
the regexp to match what you want to purge.

Right now url.purge is not available in VCL, but that is on
the list of todo items.

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