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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