> which is an error in our logging (or log aggregation) system - some requests (apparently most of the slow ones) only pass through two tiers of varnish cache and XCache will look like 
> cp1067 miss (0), cp1054 frontend miss (0)
> and not
> cp1053 miss (0), amssq43 miss (0), amssq48 frontend miss (0)
>
> (This might be a good time to ask, what do three varnish entries even mean? AFAIK we only have to tiers, front and back.)

I believe its whether you hit eqiad or not. I believe non eqiad varnish hits eventually look things up in an eqiad varnish, so in essence there are three layers for some people.

--bawolff