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

[Manik Surtani]

On 3 Apr 2009, at 14:26, Mircea Markus wrote:

> Manik Surtani wrote:
>> 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?
> I'm just thinking that if we would provide such an config param, it  
> would be hard for the users to grasp it. TBH, even the concurrency  
> level its not very easy to explain, but saying something like  
> "increase it if you see lots of timeouts" should help.
> Can't we determine it based on the LockManager's concurrency level?

Thats what I mean by a guess.  Perhaps a mix of some constant x  
numCPUs, even.

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

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




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