[infinispan-dev] Integration between HotRod and OGM

Emmanuel Bernard emmanuel at hibernate.org
Wed Jan 22 08:26:45 EST 2014 

Conceptually I like the grouping API better than AtomicMap as I don’t have to rely on a specific Infinispan type.

We do use FineGrainedAtomicMap both for the entity and the association persistence (not AtomicMap). It is particularly critical for how we store the association navigation information. I don’t want one update to literally prevent the whole association from being updated. This is the same semantic a RDBMS has and that’s why Manik and I designed the FGAM requirements.

So my question is what are the differences between the grouping API and the FGAM in particular for:

- the amount of data sent back and forth (seems like grouping is sending the data naturally per key as “delta compared to the group"
- the locking level when a new entry is added to the FGAM / Grouping API
- the locking level when a new entry is removed to the FGAM / Grouping API
- the locking level when a new entry is updated to the FGAM / Grouping API
- the overall network verbosity
- does grouping offer the same repeatable read protection that AtomicMap offers within a transaction?

I think retrying as a transaction workaround is quite fragile. We can offer it as a solution but supporting or encouraging it is another story. Unless each OGM nodes do behave like a transaction but that would be wrong. I am also concerned about reading data form a group that are inconsistent.

Emmanuel

On 21 Jan 2014, at 16:07, Mircea Markus <mmarkus at redhat.com> wrote:

> Hi Emmanuel,
> 
> Just had a good chat with Davide on this and one solution to overcome the shortcoming you mentioned in the above email would be to enhance the hotrod client to support grouping:
> 
> RemoteClient.put(G g, K k, V v); //first param is the group
> RemoteClinet.getGroup(G g) : Map<K,V>;
> 
> It requires an enhancement on our local grouping API: EmbeddedCache.getGroup(G). This is something useful for us in a broader context, as it is the step needed to be able to deprecated AtomicMaps and get suggest them being replaced with Grouping. 
> 
> This approach still has some limitations compared to the current embedded integration: 
> - performance caused by the lack of transactions: this means increased TCP chattiness between the Hot Rod client and the server. 
> - you'd have to handle atomicity, potentially by retrying an operation
> 
> What do you think?
> 
> 
> On Dec 3, 2013, at 3:10 AM, Mircea Markus <mmarkus at redhat.com> wrote:
> 
>> 
>> On Nov 19, 2013, at 10:22 AM, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
>> 
>>> It's an interesting approach that would work fine-ish for entities
>>> assuming the Hot Rod client is multi threaded and assuming the client
>>> uses Future to parallelize the calls.
>> 
>> The Java Hotrod client is both multithreaded and exposes an Async API.
>> 
>>> 
>>> But it won't work for associations as we have them designed today.
>>> Each association - or more precisely the query results to go from an
>>> entity A1 to the list of entities B associated to it - is represented by
>>> an AtomicMap.
>>> Each entry in this map does correspond to an entry in the association.
>>> 
>>> While we can "guess" the column names and build from the metadata the
>>> list of composed keys for entities, we cannot do the same for
>>> associations as the key is literally the (composite) id of the
>>> association and we cannot guess that most of the time (we can in very
>>> pathological cases).
>>> We could imagine that we list the association row keys in a special
>>> entry to work around that but this approach is just as problematic and
>>> is conceptually the same.
>>> The only solution would be to lock the whole association for each
>>> operation and I guess impose some versioning / optimistic lock.
>>> 
>>> That is not a pattern that scales sufficiently from my experience.
>> 
>> I think so too :-)
>> 
>>> That's the problem with interconnected data :)
>>> 
>>> Emmanuel
>>> 
>>> On Mon 2013-11-18 23:05, Mircea Markus wrote:
>>>> Neither the grouping API nor the AtomicMap work over hotrod.
>>>> Between the grouping API and AtomicMap, I think the one that would make more sense migrating is the grouping API.
>>>> One way or the other, I think the hotrod protocol would require an enhancement - mind raising a JIRA for that?
>>>> For now I guess you can sacrifice performance and always sending the entire object across on every update instead of only the deltas?
>>>> 
>>>> On Nov 18, 2013, at 9:56 AM, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
>>>> 
>>>>> Someone mentioned the grouping API as some sort of alternative to
>>>>> AtomicMap. Maybe we should use that?
>>>>> Note that if we don't have a fine-grained approach we will need to
>>>>> make sure we *copy* the complex data structure upon reads to mimic
>>>>> proper transaction isolation.
>>>>> 
>>>>> On Tue 2013-11-12 15:14, Sanne Grinovero wrote:
>>>>>> On 12 November 2013 14:54, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
>>>>>>> On the transaction side, we can start without them.
>>>>>> 
>>>>>> +1 on omitting transactions for now.
>>>>>> 
>>>>>> And on the missing AtomicMaps, I hope the Infinispan will want to implement it?
>>>>>> Would be good to eventually converge on similar featuresets on remote
>>>>>> vs embedded APIs.
>>>>>> 
>>>>>> I know the embedded version relies on batching/transactions, but I
>>>>>> guess we could obtain a similar effect with some ad-hoc commands in
>>>>>> Hot Rod?
>>>>>> 
>>>>>> Sanne
>>>>>> 
>>>>>>> 
>>>>>>> On Tue 2013-11-12 14:34, Davide D'Alto wrote:
>>>>>>>> Hi,
>>>>>>>> I'm working on the integration between HotRod and OGM.
>>>>>>>> 
>>>>>>>> We already have a dialect for Inifinispan and I'm trying to follow the same
>>>>>>>> logic.
>>>>>>>> At the moment I'm having two problems:
>>>>>>>> 
>>>>>>>> 1) In the Infinispan dialect we are using the AtomicMap and the
>>>>>>>> AtomicMapLookup but this classes don't work with the RemoteCache. Is there
>>>>>>>> an equivalent for HotRod?
>>>>>>>> 
>>>>>>>> 2) As far as I know HotRod does not support transactions. I've found a link
>>>>>>>> to a branch on Mircea repository:
>>>>>>>> https://github.com/mmarkus/ops_over_hotrod/wiki/Usage-guide
>>>>>>>> Is this something I could/should use?
>>>>>>>> 
>>>>>>>> Any help is appreciated.
>>>>>>>> 
>>>>>>>> Thanks,
>>>>>>>> Davide
>>>>>>> 
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>>>> 
>>>> Cheers,
>>>> -- 
>>>> Mircea Markus
>>>> Infinispan lead (www.infinispan.org)
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
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>> 
>> Cheers,
>> -- 
>> Mircea Markus
>> Infinispan lead (www.infinispan.org)
>> 
>> 
>> 
>> 
> 
> Cheers,
> -- 
> Mircea Markus
> Infinispan lead (www.infinispan.org)
> 
> 
> 
> 
> 
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