Varnish vs Squid: Which Reverse Proxy Delivers Faster, More Stable Caching?

Overview

Both Varnish and Squid are open‑source reverse‑proxy servers that can serve as high‑performance caching proxies.

Varnish is widely regarded as superior to Squid, and the following points outline its strengths and weaknesses.

Advantages of Varnish

Higher stability: under the same load, Squid experiences failures more often because it requires frequent restarts.

Faster access speed: Varnish uses the “Visual PageCache” technique, reading all cached data directly from memory, whereas Squid reads from disk.

Supports more concurrent connections: Varnish releases TCP connections faster, allowing more simultaneous connections under high load.

Selective cache invalidation: Varnish can purge parts of the cache via its management port using regular expressions, a capability Squid lacks.

Disadvantages of Varnish

Higher resource consumption: under high concurrency, Varnish uses more CPU, I/O, and memory than Squid.

Cache loss on failure: if the Varnish process hangs, crashes, or restarts, all cached data in memory is lost, causing all requests to be forwarded to the backend and potentially overloading it.