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Comment by zo1 | Hacker News Reader

Can you elaborate on the need? What possible reason, short of a very contrived one, is there for having to keep a large number of machines' clocks in-sync?

And for that matter, why would anyone build any process/system/software that requires a distributed system's machines to all have their clocks in-sync. I am baffled.

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I believe Google Spanner obsesses over timestamps quite a lot to deliver distributed transactions with something called TrueTime [1].

[1] http://research.google.com/archive/spanner.html

Well, it's a reasonable solution to some distributed problems. I imagine that many distributed algorithms can be simplified a lot of you have a reliable and accurate time source. If you can build a reliable clock at less cost (development and/or overhead) than a time-insensitive algorithm would cost, then why not do it?

Many security protocols use credentials that are only valid for a brief time. Here is a simple example of a problem caused by my server's time being more than 10 minutes off from the time on S3:

http://illuminatedcomputing.com/posts/2015/04/paperclip_expi...

Yep, security is a big one. Authentication & encryption can behave very unpredictably if your times are not in sync. So, you might not be able to login to a server, or connect via HTTPS etc

There is a simple reason why it's needed - in distributed transaction you need to establish the causality of changes. That's why truetime is needed.

Sorry - missed this somehow.

People have mentioned distributed transactions and security, another area is synchronizing modeling with (hard or soft) real time inputs from separate hardware. There are a bunch of ways to get yourself tied up in knots once at least 2 physical bits of hardware are involved.

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