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From Martin Waite <waite....@googlemail.com>
Subject Re: how to lock one-of-many ?
Date Wed, 24 Feb 2010 19:25:06 GMT

I take the point that the watch is useful for stopping clients unnecessarily
pestering the zk nodes.

I think that this is something I will have to experiment with and see how it
goes.  I only need to place about 10k locks per minute, so I am hoping that
whatever approach I take is well within the headroom of Zookeeper on some
reasonable boxes.

Is it possible for the client to know whether it has connected to the
current primary or not ?   During my testing I would like to make sure that
the approach works both when the client is attached to the primary and when
attached to a lagged non-primary node.


On 24 February 2010 18:42, Ted Dunning <ted.dunning@gmail.com> wrote:

> Random back-off like this is unlikely to succeed (seems to me).  Better to
> use the watch on the locks directory to make the wait as long as possible
> AND as short as possible.
> On Wed, Feb 24, 2010 at 8:53 AM, Patrick Hunt <phunt@apache.org> wrote:
> > Anyone interested in locking an explicit resource attempts to create an
> > ephemeral node in /locks with the same ### as they resource they want
> access
> > to. If interested in just getting "any" resource then you would
> > getchildren(/resources) and getchildren(/locks) and attempt to lock
> anything
> > not in the intersection (avail). This could be done efficiently since
> > resources won't change much, just cache the results of getchildren and
> set a
> > watch at the same time. To lock a resource randomize "avail" and attempt
> to
> > lock each in turn. If all avail fail to acq the lock, then have some
> random
> > holdoff time, then re-getchildren(locks) and start over.
> >
> --
> Ted Dunning, CTO
> DeepDyve

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