From: Chuck Remes <cremes.devlist@...>
Date: 2010-07-07T03:47:15+09:00
Subject: Re: [Q] synchronize a "mocked" clock in a distributed system

On Jul 6, 2010, at 12:52 PM, Tony Arcieri wrote:

> On Mon, Jul 5, 2010 at 3:15 PM, Chuck Remes <cremes.devlist@mac.com> wrote:
> 
>> Because there is no centralized server that all messages, data or control
>> must pass through.
>> 
> 
> If your system is fully asynchronous and there's no central data source, how
> is it possible for nodes to synchronize to a central clock?  That makes
> absolutely no sense.

I wrote a long email describing why I thought I was right, but I kept coming back to your earlier question about a centralized data source. The problem I have with my data source is that the documents within it have different time granularities for the data. For example, some documents represent data aggregated over 1m, 1 day or 1 week. Since documents of each time granularity may be requested by various processes, I didn't see how I could use them as a source for the mock clock.

And then it hit me. I could have a mock clock process that subscribes to all of those data sources and receives all of those messages. The mock clock should *only* pay attention to the document data with the smallest time granularity for setting the clock and ignore the rest.

So yes, you are right. I *do* have a central data source that I can use to set the clock. I just didn't see it before. 

Thanks for pressing me on this. It forced me to really figure it out.

cr