[infinispan-dev] Isolation level in Repeatable Read + remote get

[Galder Zamarreño]

On Jul 8, 2013, at 11:02 AM, Pedro Ruivo <pedro at infinispan.org> wrote:

> Hi guys,
> 
> re: ISPN-2840, ISPN-3235, ISPN-3236
> short: transaction isolation in repeatable read
> 
> Dan came up with an idea (a good idea IMO) to change a little the logic 
> how entries are put in the context for transactional caches.
> 
> One of the Repeatable Read properties is after a key is accessed, the 
> transaction should never see other concurrent transaction values, even 
> if they commit first. In result, we can optimize the distributed mode by 
> only do a remote get on the first time a transaction access a key.
> 
> My idea (and the one implemented in the Pull Request)

^ Which pull req, link? You mean [1]?

[1] https://github.com/infinispan/infinispan/pull/1937

> was adding a flag 
> to mark the entry as accessed. All future access to that key will not 
> try to fetch the data from container neither from a remote location (we 
> have a small but with last one).
> 
> The Dan's idea is more simple but require some change in the 
> EntryFactory logic.

^ Which is Dan's idea exactly?

> At this stage, we only put an entry in the 
> transaction context if the following conditions are respected:
> 
> * the entry exists in data container (i.e. the node is owner or it is in L1)
> * we put a RepeatableReadEntry with null value in the transaction context if
> ** the entry does not exist in the container but the node is owner
> ** the entry does not exist in the data container but the command has 
> flags to skip the remote fetch (like IGNORE_RETURN_VALUE or 
> SKIP_REMOTE_LOOKUP). Of course the conditional commands needs special 
> attention here.
> 
> Note: as usual, if the entry exists in the context, then nothing is done.
> 
> At the TxDistributionInterceptor level, the check to see if the remote 
> get should be done is simple as check if lookupEntries(k)==null.
> 
> Dan, if I said something wrong let me know. If I was not clear at some 
> point let me know too.
> 
> Anyone see any issue with this approach?
> Any other suggestions?
> 
> Cheers,
> Pedro Ruivo
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--
Galder Zamarreño
galder at redhat.com
twitter.com/galderz

Project Lead, Escalante
http://escalante.io

Engineer, Infinispan
http://infinispan.org