Sounds right to me.  Much simpler as well.

On Thu, Aug 5, 2010 at 5:38 PM, Jonathan Holloway <
jonathan.hollo...@gmail.com> wrote:

> Hi Ted,
>
> Thanks for the comments.
>
> I might have overlooked something here, but is it also possible to do the
> following:
>
> 1. Create a PERSISTENT node
> 2. Have multiple clients set the data on the node, e.g.  Stat stat =
> zookeeper.setData(SEQUENCE, ArrayUtils.EMPTY_BYTE_ARRAY, -1);
> 3. Use the version number from stat.getVersion() as the sequence (obviously
> I'm limited to Integer.MAX_VALUE)
>
> Are there any weird race conditions involved here which would mean that a
> client would receive the wrong Stat object back?
>
> Many thanks again,
> Jon.
>
> On 5 August 2010 16:09, Ted Dunning <ted.dunn...@gmail.com> wrote:
>
> > (b)
> >
> > BUT:
> >
> > Sequential numbering is a special case of "now".  In large diameters, now
> > gets very expensive.  This is a special case of that assertion.  If there
> > is
> > a way to get away from this presumption of the need for sequential
> > numbering, you will be miles better off.
> >
> > HOWEVER:
> >
> > ZK can do better than you suggest.  Incrementing a counter does involve
> > potential contention, but you will very likely be able to get to pretty
> > high
> > rates before the optimistic locking begins to fail.  If you code your
> > update
> > with a few tries at full speed followed by some form of retry back-off,
> you
> > should get pretty close to the best possible performance.
> >
> > You might also try building a lock with an ephemeral file before updating
> > the counter.  I would expect that this will be slower than the back-off
> > option if only because involves more transactions in ZK.  IF you wanted
> to
> > get too complicated for your own good, you could have a secondary
> strategy
> > flag that is only sampled by all clients every few seconds and is updated
> > whenever a client needs to back-off more than say 5 steps.  If this flag
> > has
> > been updated recently, then clients should switch to the locking
> protocol.
> >  You might even have several locks so that you don't exclude all other
> > updaters, merely thin them out a bit.  This flagged strategy would run as
> > fast as optimistic locking as long as optimistic locking is fast and then
> > would limit the total number of transactions needed under very high load.
> >
> > On Thu, Aug 5, 2010 at 3:31 PM, Jonathan Holloway <
> > jonathan.hollo...@gmail.com> wrote:
> >
> > > My so far involve:
> > > a) Creating a node with PERSISTENT_SEQUENTIAL then deleting it - this
> > gives
> > > me the monotonically increasing number, but the sequence number isn't
> > > contiguous
> > > b) Storing the sequence number in the data portion of a persistent node
> -
> > > then updating this (using the version number - aka optimistic locking).
> > >  The
> > > problem with this is that under high load I'm assuming there'll be a
> lot
> > of
> > > contention and hence failures with regards to updates.
> > >
> >
>

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