Hi, The difference from traditional clustering is there is no single mysql database so failover and replication don't need to be managed manually. Cassandra is the system where writes "take some time" to propagate but the time we're talking about is almost always less than a second. The exception is when a node becomes unreachable so changes simply cannot be propagated to that node (as was shown in the video). This matter of eventual consistency is not a bug but a very important design feature of highly scalable systems. In a traditional SQL system there is also a span of time for an update to be logged to disk, when this is happening, a lock prevents other threads from accessing that data so requests back up. With a swarm of nodes handling a flood of queries and updates, this design simply doesn't scale. For the financial industry, the row locking is an absolute necessity since a stale read could cause an account to go out of balance. For serving web pages, as long as care is taken in the storage and caching infrastructure, cutting this corner is relatively safe and highly advantageous. Thanks, Caleb On 07/04/2012 02:44 AM, Paul Libbrecht wrote:

Caleb,

can you say the difference to XWiki clustering?

Does it approach things I heard about a cloud infrastructure where data in one node "takes some time" to be propagated to other nodes?

paul

Le 4 juil. 2012 à 00:57, Caleb James DeLisle a écrit :

...

Hi,

Over in the XWiki Research Department, we've been working on some exciting new developments. While XWiki provides industry leading flexibility for defining, storing and querying data structures in SQL based stores, we are researching how to bring storage to Cassandra distributed NoSQL data store and give you the power to define and store your own true Java native Objects.

In this demonstration we run 2 integrated XWiki/Cassandra nodes and show changes propagating from one to the other as we edit pages. We show that you can stop one node and the wiki is still fully functional with only one node running. Then we restart the downed node and show the edits which were made while the node was down propagating over from the running node.

Here is the demonstration video:

http://www.youtube.com/watch?v=NngAKdeWuH0

While this is still in heavy development, we hope to be bringing up live nodes for you to play with as soon as possible.

Thanks,

Caleb

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Yes, this is exactly what I was thinking about when I designed it. I envisioned the next generation as being more powerful than the current generation in a Turing sense so that it can emulate it to provide backward compatibility. I had imagined a UI where the user selects properties in a class editor and template code is generated below which they can edit. As far as the UI goes, the sky really is the limit here. Thanks, Caleb On 07/04/2012 04:26 AM, Jerome Velociter wrote:

Hi Caleb,

This is great stuff!

Since XClasses are actually JDO-enhanced Java classes as I understand, is there, or could we add, an UI to write such classes directly (in groovy for example) ? It would offer more possibilities than regular XWiki classes : more complex relationships, other types (blobs, etc.). A mechanism would be needed to be able to manipulate such objects as native java objects from the XWiki api I guess.

Does that make sense ?

Jerome

On Wed, Jul 4, 2012 at 12:57 AM, Caleb James DeLisle < [email protected]> wrote:

...

Hi,

Over in the XWiki Research Department, we've been working on some exciting new developments. While XWiki provides industry leading flexibility for defining, storing and querying data structures in SQL based stores, we are researching how to bring storage to Cassandra distributed NoSQL data store and give you the power to define and store your own true Java native Objects.

In this demonstration we run 2 integrated XWiki/Cassandra nodes and show changes propagating from one to the other as we edit pages. We show that you can stop one node and the wiki is still fully functional with only one node running. Then we restart the downed node and show the edits which were made while the node was down propagating over from the running node.

Here is the demonstration video:

http://www.youtube.com/watch?v=NngAKdeWuH0

While this is still in heavy development, we hope to be bringing up live nodes for you to play with as soon as possible.

Thanks,

Caleb

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