[infinispan-dev] API behaviour when using DIST

[Manik Surtani]

Ok, after discussing this on IRC and the clustering conf call, here is  
what we will do:

1.  Non-transactional

* Only support DIST in SYNC mode.  Throw a configuration exception if  
DIST and ASYNC are detected.
* Allow DIST_ASYNC if an unsafe flag is set to true (breakApi=true?)  
in the config, so that the user is explicitly aware that API return  
values will be unreliable.
* Make sure this is documented in the Javadocs as well as the FAQs

2.  Transactional - Async

* As above, do not support unless breakApi = true.  In which case this  
is simple - no return values, only broadcast modifications in prepare  
as we do with REPL_SYNC.

3.  Transactional - Sync

* Offer 2 options here.  Option 1 is simple and we already have this.   
Option 2 will need to be written.

Option 1:  break API.  This will behave the same as async, in that we  
don't care about return values, but we still use a 2-phase commit  
protocol for the transaction boundary.  Users will still need to  
specify breakApi = true so this is explicit.

Option 2: Before any write RPC call is broadcast, a remote get is  
performed.  This pulls back the necessary values so that a reliable  
return value is available.

Cheers
Manik

On 17 Apr 2009, at 12:18, Manik Surtani wrote:

> This gets even more interesting when we have transactions in play.   
> E.g.:
>
> K resides on {A, B} in a cluster of {A, B, C}
>
> On C, we do:
>
> 1.  tx.begin()
> 2.  retval = C.replace(K, V, V2)
> 3.  // do something with retval
> 4.  tx.commit()
>
> It is one thing to set the expectation of unreliable return values  
> for async mode as defined below, but the above would be tricky even  
> in the case of sync mode.  On line 2 we would have to start the tx  
> on remote nodes and start processing the commands and pull back  
> results.  And on 4, the prepare logic would have to change to assume  
> that all writes have already been executed.
>
> On the plus side, this means we have txs that will fail fast(er) if  
> remote locks cannot be be acquired...
>
> Thoughts and comments?
>
> - Manik
>
> On 16 Apr 2009, at 14:33, Manik Surtani wrote:
>
>> Some of the API methods' return values may not be as expected when  
>> using DIST.  Just wanted to run this by you guys to see what you  
>> thought.
>>
>> Specifically, what I am referring to is methods like put(),  
>> putIfAbsent(), and the 2 versions of remove() and replace().
>>
>> Now when these are executed in any other cache mode (LOCAL, REPL,  
>> INVAL) return values are as expected from their java.util.Map  
>> contracts.
>>
>> However with DIST, there are 2 separate ways this could go.
>>
>> 1.  The key in question is mapped to the local cache on which the  
>> method is invoked.
>>
>> This case behaves normally as well as per the Map contract.
>>
>> 2.  The key in question is *not* mapped to the local cache.  E.g.,  
>> K is mapped to nodes A and B, and on C we do C.remove().
>>
>> I can stick with the map contract if each of these methods first  
>> does a remote lookup of the key and stores this in L1 (or even in  
>> the invocation context and then throw it away if there is no L1)  
>> but this is unnecessarily wasteful IMO.
>>
>> The other approach is to realise the command pertains to a key for  
>> which the local cache is not the owner, and replicate the call to  
>> the remote nodes.
>>
>> What happens next is also a matter of tuning:  we could
>>
>> a) replicate + ignore responses.  Then the retval to these methods  
>> are indeterminate, and probably unusable.
>> b) replicate + wait for response.  This will adhere to the Map  
>> contract, albeit at a cost.  Probably not possible if we use  
>> DIST_ASYNC.
>> c) L1: we could either "correct" the L1 cache with the change, or  
>> remove the key forcing another lookup for the next time around.
>>
>> What do people think?  Maybe offer all strategies?  Or will this  
>> then become configuration hell?  :)
>>
>> Cheers
>> --
>> Manik Surtani
>> manik at jboss.org
>> Lead, Infinispan
>> Lead, JBoss Cache
>> http://www.infinispan.org
>> http://www.jbosscache.org
>>
>>
>>
>>
>> _______________________________________________
>> infinispan-dev mailing list
>> infinispan-dev at lists.jboss.org
>> https://lists.jboss.org/mailman/listinfo/infinispan-dev
>
> --
> Manik Surtani
> manik at jboss.org
> Lead, Infinispan
> Lead, JBoss Cache
> http://www.infinispan.org
> http://www.jbosscache.org
>
>
>
>

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