memcached

[Matthew Glubb]

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I regularly use a locking mechanism with memcache. Fortunately in my  
situation, if a process fails to acquire a lock (usually due to a  
lock wait timeout), it isn't the end of the world as its self healing.

Depending on what you want to do, your mileage may vary. I would  
hesitate in waiting more than 10-20 milliseconds in a lock wait. But  
then, I am using PHP which is disastrous for concurrent programming : 
( The next version is in Python :)

Regards,


Matt

On 14 May 2007, at 17:57, Dustin Sallings wrote:

>
> On May 14, 2007, at 8:25 , Julio Leyva wrote:
>
>> We have a transaction that must lock a key in a table and no any  
>> other parallel transaction can access that key until the first  
>> transaction is finished.
>>
>> We think that process will be faster using memcached.
>
> 	The best that memcached could offer is a counter you could do  
> something like a spinlock on.  That may very well be worse.
>
> 	It should be possible to parallelize your transactions, though.   
> Should all read processes stop just because something has indicated  
> it may be changing in another process?  If you allow concurrent  
> reads, then you memcache can help, but you can likely do away with  
> the lock altogether.
>
> 	If you can defer  your concurrency checking to the *end* of the  
> transaction, all you have to do is roll back whatever transaction  
> didn't win and start it over.  I used to do something like this for  
> a relatively concurrent system.  In my case, the number of  
> transaction collisions was small enough that I never even bothered  
> to replay the loser.  I'd just roll it back and return an error and  
> let the other side deal with the failure.  I tracked all of the  
> fields that changed, so resolving it would've been pretty simple,  
> though.
>
> -- 
> Dustin Sallings
>
>



m a t t h e w   g l u b b

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