[infinispan-dev] The meaning of "concurrency level"

[Manik Surtani]

This is an attribute in the <locking /> configuration element and is  
used to define the number of lock stripes used by the LockManager,  
*if* striped locking is used.

Now I wonder whether we need a tuning parameter of this sort in the  
data container as well.  Consider that the SimpleDataContainer is  
backed by a CHM and the FIFO and LRU variants are backed by something  
very similar to a CHM (in that there are lockable segments which  
contain hash tables).  In both cases, I use default concurrency levels  
(16 segments), but maybe this should be configurable too?  Should this  
be a separate attribute, or could "concurrencyLevel" be reused here?

The way I see it, LockManager needs a higher number of stripes since  
transactions could span keys that are in > 1 stripe.  Segments,  
however, are only locked for the duration of a write access to the  
container which is a) typically very short and b) usually limited to  
the number of active threads, which is related to the number of cores/ 
CPUs.

Basically, what I am saying is that the latter could probably be  
guessed/hard coded rather than made configurable, and even if made  
configurable, is unlikely to be the same as the number of stripes used  
by the LockManager.

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




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