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From Stefan Guggisberg <stefan.guggisb...@gmail.com>
Subject Re: Clustering w/ distributed cache
Date Wed, 18 Feb 2009 14:01:48 GMT
On Mon, Feb 16, 2009 at 9:02 PM, defeng <defeng.lu@gmail.com> wrote:
>
> I am using Jackrabbit 1.4.4 clustering. DB for persistent manager, and NFS
> for datastore. Everything works well, but since the Jackrabbit uses a
> Cluster-wide lock, many times, other JCR clients need to wait for a long
> time to acquire the Global lock.
>
> To solve this issue, I want to use a distributed cache(memcached) in
> SharedISM. To disable cache in SessionISM and LocalISM (I did not use XA ).
> So there is no necessary to sync any data in cache. In addition, I donot
> need to register Namespace or Nodetype at runtime. The only thing is to sync
> local search index in the Looping of ClusterNode. (I did not use
> AccessManager in Jackrabbit)
>
> When updating an item, a distributed lock is acquired. It is used to ensure
> the data consistence between persisten manager and distributed cache
> (2-phase commit).
>
> Is the proposal feasible? Any comment is highly appreciated!

i don't think that this would work without a major redesign of jackrabbit's
core architecture.

SharedISM caches ItemState instances read from the PM. this
memory-sensitive cache, apart from helping to reduce PM calls,
guarantees that there's only *one* ItemState instance for any given id
on this layer. similarly, 'caches' in SessionISM and LocalISM are
crucial for jackrabbit's support of isolation levels. changing the
semantics/behavior of those 'caches' would easily lead to data
corruption/lost updates etc.

cheers
stefan

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