[infinispan-dev] Write skew check implementation

[Galder Zamarreño]

Hi Pedro,

I assume that by partial replication mode you meant distributed mode (using consistent hash algorithm)?

Hmm, why should n2 send the value of d before writing? n1 is an owner of d, so n1 should have that value.

I'm not sure I'm understanding your question correctly.

Cheers,

On Jun 13, 2011, at 7:05 PM, Pedro Ruivo wrote:

> Hi,
> 
> I am progressing with my implementation of total-order-based commit 
> protocol for the partial replication mode, and I would be grateful if 
> you could help me understanding how the write skew check is implemented 
> in ISPN.
> 
> Assume the scenario in which a node, say n1, that owns a data item d 
> receives a prepare message for a transaction, say T, originated on 
> different replica n2.
> 
> Of course write skew check is enabled.
> 
> After n1 acquiring the lock on d, it should check whether the value of d 
> read during T's execution is still the most recently committed one.
> 
> I may be missing something here, but looking at [1] (lines 160 to 168) 
> and [2] at copyForUpdate method, n1 is reading twice the value of d that 
> is locally stored (once in line 160([1]) to create the 
> RepeatableReadEntry and a second time in line 52([2]) to do the write 
> skew check).
> 
> I would have expected that the node that originated the transaction 
> would send the values that it read (before writing them) in piggyback 
> with the prepare message, in order to allow the "owners" to perform the 
> write skew.
> 
> Thanks
> 
> Pedro
> 
> [1] 
> https://github.com/infinispan/infinispan/blob/master/core/src/main/java/org/infinispan/container/EntryFactoryImpl.java 
> 
> [2] 
> https://github.com/infinispan/infinispan/blob/master/core/src/main/java/org/infinispan/container/entries/RepeatableReadEntry.java
> 
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> 
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--
Galder Zamarreño
Sr. Software Engineer
Infinispan, JBoss Cache