[infinispan-dev] Rehashing for DIST

[Manik Surtani]

On 6 May 2009, at 10:09, Manik Surtani wrote:

>
> Let me have a think, this may well still be workable.

Here is why I had issues with this approach - it still lacks some  
consistency when you have concurrent writes.   Pretty much what we saw  
with state transfer.

E.g.:

V0: {A, B, C}
V1: {A, B, C, D}

K -> {A, B} (V0)
K -> {B, C} (V1)

The problem lies when you have the rehash in progress.  For example,  
if we assume it is A's job to push K to C.  While this is happening, B  
updates the value of K from V1 to V2.  Even if B uses a union of the  
sets and invokes the put(K, V2) on {A, C}, we still are exposed to a  
race between this put, and A pushing (K, V1) to C.

This is why with state transfer we either (a) stop the cluster  
(FLUSH), or (b) use NBST, which records transactions in-fly during the  
period of the transfer, and replay the transactions again on the  
joiner in order.


--
Manik Surtani
manik at jboss.org
Lead, Infinispan
Lead, JBoss Cache
http://www.infinispan.org
http://www.jbosscache.org