Re: [infinispan-dev] eager locking and async replication
Let me detail on this a little more: the optimisation refers to cache.lock() not to
perform remote locks on ALL data owners, but only on the main data owner.
This way , if session affinity is used for enforcing key locality then cache.lock() would
only acquire lock within the same JVM - i.e. very good performance without loosing
eager's locking semantics. If the cluster changes, and the key is rehashed on a
different node, than eager locking would do an RPC - but for many clusters the topology
changes are infrequent.
Another problem that raises is that of consistency during node failures: if K is on node A
and it was locked by a tx originated on node B. If A fails then we can invalidate the
transaction on B, so that it would rollback.
Another interesting race condition Sanne raised is with re-hashing: "it needs to be
atomic to know who is the owner and aquire the lock, or the owner might be moved and
you're locking on the wrong node (only)"
I think this is not related to this optimisation in particular, but stands for eager
locking in general - any idea how this is handled btw?
Cheers,
Mircea
On 20 Aug 2010, at 11:04, Manik Surtani wrote:
Not sure I understand - are you proposing that the RPC for
LockControlCommands are always async if the keys are generated using the key affinity
service?
On 19 Aug 2010, at 16:29, Mircea Markus wrote:
> Hi,
>
> Here is the scenario, N=numOwners
>
> TM.start()
> c.lock(a); //this makes N (might me less) RPCs to acquire locks
> c.get(a)
> ...
> TM.commit(); // this would do an N calls for prepare/commit. Might happen async.
>
> By using the key affinity service, one might enforce a tx to operate on
"local" keys (i.e. keys that are hashed on the same node where the tx was
started).
> Now, if we would be able to *only* eager lock the main data owner (v.s. N RPCs for
lock acquisition locks) than eager locking would be as fast as the non-eager locking for
this scenario.
> What happens with the TX if the data owner crashes and only one copy is locked? We
would need to invalidate the transaction at originator's side, which I think is
possible.
> For async repl with N >= 2 and key affinity the performance benefit for eager
locking would be close to local puts: which is huge.
>
> This use case was brought by Erik ( cc)- please add you comments if something is
missing. What do you think about this optimisation?
>
> Cheers,
> Mircea
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--
Manik Surtani
manik(a)jboss.org
Lead, Infinispan
Lead, JBoss Cache
http://www.infinispan.org
http://www.jbosscache.org
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