On 1/27/2007 7:26 AM, Gregory Stark wrote:
Jan Wieck <[EMAIL PROTECTED]> writes:
I think the system I described is a slightly modified Lamport generator. The
maximum timestamp of any row updated in this transaction, you can consider that
the "counters received from other nodes". Then I make sure that the next
counter (timestamp) is higher than anything I know so far, and I add
cluster-wide unique tie breaker to that.
If you know all the timestamps in the system then you don't need timestamps at
all, just use a counter that you increment by one each time.
Isn't the whole reason people use timestamps is so that you don't have to
depend on atomically knowing every timestamp in the system? So two
transactions can commit simultaneously on different systems and use the
timestamps to resolve conflicts later.
This assumes that you never lose contact to the cluster or if so,
instantly stop all update activity because you are at risk that the
counters diverge. This risk is much higher with a simple counter than
with a system clock that was in sync at the time of disconnect.
With all the disadvantages and the pain factor of an asynchronous
multimaster replication system comes one big advantage. You can continue
autonomously and let conflict resolution figure it out later.
Jan
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