[infinispan-dev] Func API in tx cache

[Radim Vansa]

Hi,

seems I'll have to implement the functional stuff on tx caches [1][2] if 
I want to get rid of DeltaAware et al.

The general idea is quite simple - ReadOnly* commands should behave very 
similar to non-tx mode, WriteOnly* commands will be just added as 
modifications to the PrepareCommand and ReadWrite* commands will be both 
added to modifications list, and sent to remote nodes where the result 
won't be stored yet.
The results of operations should not be stored into transactional 
context - the command will execute remotely (if the owners are remote) 
unless the value was read by Get* beforehand.

With repeatable-reads isolation, the situation gets more complicated. If 
we use ReadOnly* that performs identity lookup (effectively the same as 
Get*) and the entry was modified in during the transaction, we can 
return two different results - so a read committed semantics. With write 
skew check enabled, we could at least fail the transaction at the end 
(the check would be performed reads as well if the transaction contains 
functional reads), but we cannot rely on WSC always on with RR.

Retrieving the whole entry and applying the functional command is not a 
viable solution, IMO - that would completely defy the purpose of using 
functional command.

A possible solution would be to send the global transaction ID with 
those read commands and keep a remote transactional context with read 
entries for the duration of transaction on remote nodes, too. However, 
if we do a Read* command to primary owner, it's possible that further 
Get* command will hit backup. So, we could go to all owners with Read* 
already during the transaction (slowing down functional reads 
considerably), or read only from primary owner (which slows down Get*s 
even if we don't use functional APIs - this makes it a no-go). I am not 
100% sure how a transaction transfer during ST will get into that.

We could also do it the ostrich way - "Yes we've promissed RR but Func 
will be only RC". I'll probably do that in the first draft anyway.

Comments & opinions appreciated.

Radim

[1] https://issues.jboss.org/browse/ISPN-5806
[2] https://issues.jboss.org/browse/ISPN-6573

-- 
Radim Vansa <rvansa at redhat.com>
JBoss Performance Team