You may notice that Varnish works well, but sometimes it completely loses the cache as the child process of Varnish is reloaded. This may be version independent and is accompanied by various errors, such as this one:
Varnish can fail not only because of misconfigured transient cache. It can fail because of bugs, for example in using libexecinfo. Sometimes you can see that Varnish’s child process fails and you lose all the cache due to it.
As you know, Varnish is a powerful caching system and it is a must-have on every Magento setup, even at the development workstation. But there is a little trick that very few people know about. It is the Transient cache, which I explain below.
You can reload Varnish config without losing your cache. To do this, you should use the standard varnishadm CLI utility.