On 6/24/2011 2:09 PM, Jim Newsham wrote:
On 6/24/2011 9:28 AM, Yang wrote:
without a clear description of your pseudo-code, it's difficult to
say whether it will work.
but I think it can work fine as an election/agreement protocol, which
you can use as a lock to some degree, but this requires
all the potential lock contenders to all participate, you can't grab
a lock before everyone has voiced their vote yet
I agree with this statement. I think the issue is that the timestamps
are generated by the clients and their clocks may not be in sync, so
write A from client A might arrive with timestamp T, and write B from
client B may reach the node later in time, however it may have an
earlier timestamp (T', where T' < T). Client A may perform a read
immediately after its write and notice that it was the only client to
request a lock -- so it will assume it has acquired the lock. After
Client B's lock request, it will perform a read and observe that it
has written the request with the earliest timestamp -- so it will also
assume it has acquired the lock, which would result in a failure of
the locking scheme. If each client is required to wait for all other
clients to "vote", then this issue goes away.
Yes, you both understand the problem. Hopefully we can find a solution
without relying on a hack and based on C* design that will be supported
in the future.
I'll be thinking on this some more. Thanks.
