[jboss-cluster-dev] JGroups configurations in JBoss AS 5

[Manik Surtani]

On 24 Feb 2009, at 16:41, Bela Ban wrote:

>
>
> Manik Surtani wrote:
>> Yes, but it relies on an open stream between the 2 instances.   
>> State is written without a flush, and then a marker is placed on  
>> the stream asking the state requester to start a partial flush so  
>> that the final tx log can be written to the stream as well.
>
> IIRC the marker is on the TX log, so you can use either streaming or  
> regular state transfer. Whether or not we use streaming state  
> transfer should be hidden from the caller of Channel.getState()

Nope.  Regular state tfr will wait till the entire state is ready and  
then transfer the byte buffer.  This is no good for NBST since, with  
NBST, here is what happens:

1.  Joiner (Cache B) joins, requests state from Cache A
2.  A generates and starts streaming state to B
3.  When state is transferred, A starts streaming tx log
4.  When remaining tx log is small, A puts a marker on the stream
5.  B sees this marker and requests a flush
6.  Once flush is detected by A, write remaining tx log and *this*  
ends the state transfer process.
7.  B releases the flush

So when using regular state tfr, B will not see the marker placed by A  
in step 4, since the stream is flushed to a byte buffer and  
transferred in 6.  A will never get to step 6 until B starts a flush  
in step 5.  And for this to happen, state needs to stream across  
constantly and not wait for the state generation process to complete.

>
>
> -- 
> Bela Ban
> Lead JGroups / Clustering Team
> JBoss - a division of Red Hat

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




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