Varnish, long lived cache and purge on change

Rob S rtshilston at
Wed Aug 19 18:00:10 CEST 2009

Poul-Henning Kamp wrote:
> My only worry is that it adds a linked list to the objcore structure
> taking it from 88 to 104 bytes.
I realise this could be undesirable, but at the moment varnish is 
proving quite difficult to use in sites that frequently purge, with 
different users adding their own workarounds (versioning URLs, 
restarting Varnish, tweaking the hash key etc).  Everything is a trade 
off, but I think it's desirable to increase the memory footprint per 
object so as to not bring down the server with massive memory growth.

> Probably the more interesting question is how aggressive you want it to
> be: if it is too militant, it will cause a lot of needless disk activity
I feel that some sort of hysteresis on the size of the purge list would 
make most sense, perhaps starting to process if the list exceeds more 
than X bytes, and stop when the list is < Y bytes.

Having thought a little more about this, I realise I don't know whether 
graced requests respect bans.  If they don't, then processing the ban 
list will change Varnish's behaviour. 


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