Using varnish to increase the cache time of slow pages

Thiago Figueiro TFigueiro at
Mon Mar 12 23:21:50 CET 2012

Hi, Jonathan.  Thanks for the feedback!

> However, I have a couple of quibbles with this *implementation*:
> 1) Every bit of logic you embed into VCL is something you have to work at

It's fair to note that other web framework engines seem to use the X-Runtime header for this purpose.

But yes, I agree, you might have to implement that in your backend.

> munging the TTL in VCL!), fixing your back-end's code so it outputs the
> right caching headers, possibly using the same methodology, is a more
> significant win. IMHO :-)

Ah!  No need to put salt in our sores. :)

What typically happens is that new features are prioritised over improving performance.  I think this is a sad reality in many companies.

What little effort goes into performance ends-up being "spread" across the application.  If you have editors complaining about content freshness you can now target these specific pages.

> 2) From a more concrete PoV, I'm not sure this code copes well with
> content the back-end explicitly marks as non-cachable (i.e. ttl=0).

We have specific code in our VCL for this and assumed everyone else does.  I should have mentioned that when this excerpt runs we have already 'passed' content which is not cacheable.

> Anyway, thanks for introducing the concept! Sorry if this looks a bit
> negative - it's not really meant to come over as such :-)

Not negative at all, they were all good points and I appreciate you taking the time to ping back.


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