Gzipping and shielding


I have noticed that our site is showing sometimes as ‘Gzipped’ enabled when running Google’s speed tester, and other times it’s not showing any compression and so scores badly.

I’ve used other Gzip tests and one site first said we were not but then after a refresh it said it were! The page in question had been cached for 30 mins at the stage of testing so it’s not like a new version appeared.

I can only think this might have something to do with different POPs / shielding showing different versions of our site. Could this be the case, has anyone experienced anything similar?



If you’re seeing intermittent gzipping it may be because the Vary header isn’t being used and the compressed and uncompressed versions of the object are being stored separately. If that is the case, the object that is cached and returned will depend on which one is requested first by a node in the POP.

I’d recommend sending in a support ticket to support@fastly.com. We can always circle back here to provide the answer if it is different! :slight_smile:


Hi Justin

Thanks, I’ve actually contacted you in relation to this before and had checked the Vary header which seems fine. The strange thing in this case is the two tests were performed while the object was still in cache (using the ‘age’ as the factor determining this). So the homepage was cached for 30 mins and a few tests on gzipping were performed. Google speed test said ‘No Gzip’ while looking in Chrome / FF and testing using other online services all said ‘Gzip enabled’. This was within seconds of each other and the age of the object did not reset.

It’s confusing but obviously we’re concerned if Google thinks our site is slower than it actually is.


It sounds like a problem with the test rather than anything else, to be honest!
In any case, this isn’t something we’re likely to be able to diagnose here, so a Support ticket is your best bet.