From: David Masover <ninja@...>
Date: 2008-09-28T12:29:47+09:00
Subject: Re: How to make Ruby _THE_ scripting language of choice, fold in SQLite

On Saturday 27 September 2008 20:34:32 Clifford Heath wrote:
> David Masover wrote:
> > Again, it's difficult to argue against this when you haven't told me which 
> > ones aren't supported, and why.
> 
> DVCS exists because isolation isn't needed, since tools like patch
> can often resolve conflicts and when they can't, a human can.

DVCS does, in fact, provide isolation (most checkouts are not public until 
pushed to a public server).

And tools like patch are severely limited by not actually knowing much about 
the application at hand. Most newer VCSes are much smarter about resolving 
conflicts, but at a certain point, since the VCS doesn't actually know what a 
certain line of code does, it can't necessarily know which version of that 
line is the correct one -- it can only guess from context.

Compare this to application-specific conflict resolution -- it's quite 
possible that simply examining the two conflicting states is enough to decide 
which is correct.


> > I'll go read the Dynamo paper again, then...
> 
> From <http://www.allthingsdistributed.com/2007/10/amazons_dynamo.html>:
> "To achieve this level of availability, Dynamo sacrifices consistency under 
certain failure scenarios."

From the same article:

"Dynamo is used to manage the state of services that have very high 
reliability requirements and need tight control over the tradeoffs between 
availability, consistency, cost-effectiveness and performance."

But you're right here, and I withdraw any claim of solid ACID properties of 
Dynamo. I do agree with this, though:

"Experience at Amazon has shown that data stores that provide ACID guarantees 
tend to have poor availability. This has been widely acknowledged by both the 
industry and academia."