[mibbitier]

huh? Infrastructure is totally and utterly irrelevant to the problem. I know enough about common sense to make such a claim.

Just send a new message, exactly as you would post an original item/comment/etc, but have some special text/field in there that says "please ignore the previous message". The UI would then hide the previous message.

eg

  COMMENT: {id:9374758, from:"mibbitier", data:"I hate you all!"}
  COMMENT: {id:9374759, from:"mibbitier", data:"*IGNORE_MESSAGE_IN_UI* 9374758"}

Nothing whatsoever to do with infrastructure. Nothing to do with caches. Purely to do with the UI. Not rocket science.

Granted, it's a poor way to do it, but it's better than nothing, and easier than trying to invalidate caches etc

[nthj]

Here's the thing that customers, managers, and less experienced developers all have in common: they understand that no one thing is difficult. But they don't take into account that managing the complexity between a thousand, or a hundred thousand, or a million rules is very, very difficult.

That's why you hire more experienced developers: they're more experienced, not at things like cache invalidation (sure, just nuke your entire cache anytime anything changes! easy!), but at managing complexity.

Which is difficult.

That's why I try to keep my mouth shut about how somebody should "just do this, it'd be so easy, why are they dumb?"

[mh-]

I'm sure it's already rendered to a static presentation-level (HTML/template language du jour) form at that point. That wouldn't work.

[mibbitier]

Just put some more javascript in there to deal with it. I'm sure it's not the hardest problem in the world.

[engtech]

Great, you've hidden the message with javascript, but now it's still in view-source and in search results for bots.

It's also still visible if someone is using noscript (actually, I have no idea if Facebook works with noscript, probably not).

The solution you are suggestion doesn't solve the problem and injects more corner cases.