[Brybry]

I caught a bug related to this in Project Zomboid in an early multiplayer version.

Often when someone joined a server there would be a tiny bit of lag for all of the users.

I figured out the server was using a java method that indirectly was doing a blocking DNS lookup. I think it was reverse DNS but I forget which method it actually was, and if it was blocking the main thread or just the networking thread.

(PiHole still wouldn't have created an additional cost though.)

[simon04]

This issue might relate to Java's URL class equals/hashCode doing DNS lookups which is specified in Javadoc https://docs.oracle.com/javase/8/docs/api/java/net/URL.html#... but reported by various linters such as https://errorprone.info/bugpattern/URLEqualsHashCode

[charleslmunger]

Very likely URL.equals()

[milgrim]

My question was meant rhetorically, but I guess there might be some even more interesting exceptions to this out there.