[hibernate-dev] [OGM] Ogm mass indexer, how to convert Tuple/EntityKey to Entity/Id?

Davide D'Alto daltodavide at gmail.com
Wed Mar 6 10:32:23 EST 2013 

it's ok for me

Davide

On Wed, Mar 6, 2013 at 3:28 PM, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
> I'm planning on working on OGM-151. Fine with everyone?
> That will likely be my last before I move back to BVAL and close the
> final issues there.
>
> Emmanuel
>
> On Tue 2013-03-05 19:04, Sanne Grinovero wrote:
>> Nice!
>> n+1 is something Hibernate Search has to deal with too, that's why I
>> was interested in the fetch profiles and graph loading in JPA 2.1
>>
>> On 5 March 2013 17:44, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
>> > I have implemented a solution that gives an entity based on a tuple.
>> > https://hibernate.onjira.com/browse/OGM-273#comment-50082
>> >
>> > Note that it does not currently works for MongoDB, but that's waiting
>> > for the dedicated GridDialect method as well as OGM-151.
>> > Also note that I have no idea how that will work for associations. I
>> > suspect some nasty n+1 is happening as best. Worse case, an exception :)
>> >
>> > Emmanuel
>> >
>> > On Tue 2013-03-05 10:30, Emmanuel Bernard wrote:
>> >> We might hope for a stable enough contract on Hibernate Search and
>> >> hope that we won't break serializability between micro or minor
>> >> versions. That will need to be taken into account in the test suite and
>> >> design.
>> >> On the OGM side though, we are not at that level of maturity and we will
>> >> force homogenous Hibernate OGM version across all the cluster. The grid
>> >> will have to go down for upgrades or enforce that no mpa reduce job
>> >> using OGM is used while the version roll out is in process.
>> >>
>> >> Emmanuel
>> >>
>> >> On Mon 2013-03-04 18:30, Sanne Grinovero wrote:
>> >> > Found an example, this is all the code it needs to have a MassIndexer working
>> >> > on top of Infinispan's Map/Reduce:
>> >> >
>> >> > https://github.com/infinispan/infinispan/blob/master/query/src/main/java/org/infinispan/query/impl/massindex/IndexingMapper.java#L40
>> >> >
>> >> > Note it's initialize method which injects needed components; the
>> >> > implementation is serialized across nodes.
>> >> >
>> >> > Sanne
>> >> >
>> >> > On 4 March 2013 18:26, Sanne Grinovero <sanne at hibernate.org> wrote:
>> >> > > We finished this discussion on IRC, in case someone else was interested:
>> >> > >
>> >> > > <sanne> hum I forgot the first step.. transformation from entry into entity
>> >> > > <sanne> updated
>> >> > > <sanne> emmanuel, the "hidrate" step is what DavideD is bashing is
>> >> > > head against, but let's assume he finds a workaround and we focus on
>> >> > > the pattern as first step?
>> >> > > <emmanuel> https://gist.github.com/emmanuelbernard/5084039
>> >> > > <emmanuel> sanne: ^ that's how I would do it if I had an Iterator from the tuple
>> >> > > <emmanuel> assuming pushToExecutor pushes to whatever concurrent work
>> >> > > mechanism you planned to use on consumes
>> >> > > <emmanuel> Plus I am not folloing exactly how you plan consumes(Entry)
>> >> > > to be executed concurrently
>> >> > > <emmanuel> is that the GridDialect responsibility?
>> >> > > <emmanuel> That looks like a lot of work on the dialect's side
>> >> > > <sanne> emmanuel, imagine the backend is Infinispan and has some large
>> >> > > amount of data per node, plus that each node has its own backend
>> >> > > IndexManager (like and ideal sharding)
>> >> > > <emmanuel> ie pool mgt and cap +  queuing
>> >> > > <sanne> then with your approach the iterator needs to fetch data from
>> >> > > all remote nodes, and then enqueue in a local blocking queue which is
>> >> > > returning the data to the original owners
>> >> > > <sanne> but if you skip that step, you can just forward the statless
>> >> > > consumer to each node and have it run on data locality
>> >> > > <emmanuel> I was thinking that if you had the luncene index locally on
>> >> > > each node you would ahve a different impl of the MassIndexer anyways
>> >> > > <emmanuel> that would simply send a command to each local node
>> >> > > <sanne> To answer your question: that would be an optional GridDialect
>> >> > > responsibility. I would endorse a trivial first draft doing a
>> >> > > single-threaded loop.
>> >> > > <emmanuel> and have GridDialect.getDataFor() returnlocal data
>> >> > > <sanne> The "consumes" implementation can be either implemented with a
>> >> > > simple iterator - as in your design - so I don't think it pushes much
>> >> > > complexity to the GridDialect implementor?
>> >> > > <sanne> The benefit of the consumer is that *optionally* it can be
>> >> > > mapped on the Map phase, and that's trivial if your backend supports
>> >> > > Map/Reduce
>> >> > > <emmanuel> sanne: I don't follow that soory
>> >> > > <emmanuel> how does that make it mappable to the Map phase?
>> >> > > <sanne> "public void consume(Entry e) " is a degenerate (simplified)
>> >> > > form of map.
>> >> > > <sanne> mm infinispan IDE crashes at the right moment.
>> >> > > <emmanuel> I thought Map was about *filtering*
>> >> > > <emmanuel> not processing
>> >> > > <sanne> you can decide to accept 100% of values (without filtering),
>> >> > > but actually you might want to filter on the specified tables only.
>> >> > > <sanne> also, the return type doesn't have to match the input type:
>> >> > > hence you define a transformation function, which is inherently
>> >> > > applied in parallel on all matching entries.
>> >> > > <emmanuel> sanne: but then you require the OGM code to be everywhere
>> >> > > (ie on each node of the targetNoSQL
>> >> > > <emmanuel> to eb able to do tuple -> entity
>> >> > > <emmanuel> that's not realistic
>> >> > > <emmanuel> assuming your transform phase is about tuple -> entity and
>> >> > > some HSearch ops
>> >> > > <sanne> yes right
>> >> > > <sanne> but isn;t it worth it? it's optional and much more efficient,
>> >> > > as you avoid transferring any data.
>> >> > > <sanne> btw we often assume all nodes in the grid are equally
>> >> > > configured, so having same apps & libraries deployed.
>> >> > > <emmanuel> sanne: let me try and summarize what I understand
>> >> > > <emmanuel> it's more efficient if you store the Lucene index locally
>> >> > > with the data, and if the grid is written in Java or at least can run
>> >> > > code in Java including libraries and if you distribute the OGM
>> >> > > configuration across the whole grid
>> >> > > <emmanuel> Otherwise, it does not make any difference
>> >> > > <emmanuel> Also the GridDialect implementation need to know if you are
>> >> > > doing this trick to only return local data
>> >> > > <sanne> no there are other drawbacks which get defeated, but minor so
>> >> > > I didn't mention them
>> >> > > <emmanuel> am I right?
>> >> > > <sanne> mainly, you skip the need for the contentions point as there
>> >> > > is no push to a shared blocking queue
>> >> > > <sanne> no the GridDialect doesn't need to know.
>> >> > > <emmanuel> sanne: sure if you can process the code on each node you
>> >> > > avoid the shared blocking queue, at lest until you reach the
>> >> > > IndexManager
>> >> > > <sanne> you'll just forward a simple (standard) M/R task, and it will
>> >> > > need to execute it as always.
>> >> > > <sanne> the IndexManager is parallel ;)
>> >> > > <emmanuel> sanne: parallel on a single node
>> >> > > <sanne> yes, but no contentions points other than the internal
>> >> > > structure of the IW
>> >> > > <emmanuel> I mean updating the index for a given table is better done
>> >> > > on a singlle node
>> >> > > <sanne> IndexWriter
>> >> > > <emmanuel> sorry I meant IndexWriter
>> >> > > <emmanuel> ah but ou mention perfect sharding
>> >> > > <emmanuel> you need cosmological alignment for this shit to happen
>> >> > > <sanne> not if we plan for it :)
>> >> > > <sanne> you might remember the changes to Segments in the ISPN code,
>> >> > > to accomodate index storage consistent with the data locality
>> >> > > <sanne> that's expected in 6.0
>> >> > > <emmanuel> So gridDialect.getData(Consumer consumer, String.. tables) is wrong
>> >> > > <emmanuel> it's more gridDialect.getData(ConsumerImpl.class, String... tables)
>> >> > > <emmanuel> as you ened to send the Comsumer impl
>> >> > > <emmanuel> not simply use it
>> >> > > <sanne> hu, it needs a reference to the current SearchFactory at very least
>> >> > > <emmanuel> sanne: but you're telling me you send the M/R task
>> >> > > <emmanuel> so you need to send the M/R code as well
>> >> > > <sanne> yes but here we enter Infinspan specific implementation
>> >> > > <sanne> I would register the needed components in Infinispan and use
>> >> > > the ServiceRegistry to look them up remotely
>> >> > > <sanne> not to mention Infinispan could accomodate a custom command for it
>> >> > > <emmanuel> What I am saying is that you don't pass the Consumer
>> >> > > *instance* tot he grid dialect but rather the impl, no?
>> >> > > <sanne> the impl class definition?
>> >> > > <emmanuel> sanne: you tell me. How do I send M/R code today?
>> >> > > <emmanuel> certainly not an impl instance
>> >> > > <sanne> yes you do
>> >> > > <sanne> JBMar will take care of it, including state.
>> >> > > <sanne> but in this case that would be wrong of course as I don't want
>> >> > > to serialize the whole SearchFactory so I'd use injection and lookup,
>> >> > > but that's a detail of Infinispan.
>> >> > > <sanne> But this shouldn't be MassIndexer specific right? it's good to
>> >> > > expose a general "execute on all" method, and I think accepting
>> >> > > instances would make life easier for most - even though we might need
>> >> > > to document some limitations.
>> >> > > <emmanuel> alright, I guess 'll have to live with a visitor pattern
>> >> > > for a feature that has 5% chance of happening :)
>> >> > > <sanne> I'm going to punch Davide
>> >> > > <sanne> as he's yelling "it's not a visitor" but doesn't have the guts
>> >> > > to write it down :)
>> >> > > <emmanuel> sanne: DavideD 's would have nothing to do about it, that's
>> >> > > requires a lot of config and Infinispan machinery I'm not sure is here
>> >> > > today
>> >> > > <DavideD> :)
>> >> > > <emmanuel> ah
>> >> > > <emmanuel> I don't care how it's called, it's one of those patterns
>> >> > > that make the code harder to follow
>> >> > > <DavideD> I was actually trying to remember the name of the pattern
>> >> > > <sanne> ok now we agree :)
>> >> > > <emmanuel> Obfuscator pattern family
>> >> > > <sanne> very popular among consultants, I don't understand why you complain :P
>> >> > > <sanne> Anyway, let's wrap up and broaden the horizon:
>> >> > > <emmanuel> ok so we are left with findin to to load a entity from a tuple
>> >> > > <sanne> you don't think it's useful as a general purpose method?
>> >> > > <emmanuel> sanne: wil be for queries
>> >> > > <emmanuel> It's just that it's non obvious
>> >> > > <sanne> Exactly. Also I think lambda methods are getting widely better known.
>> >> > > <emmanuel> syntactically yes
>> >> > > <emmanuel> VM wise, perf improvements will come later
>> >> > > <sanne> what I mean is that by defining the SPI this way, I don't
>> >> > > expect it to be more complex for the GridDialect implementors, while
>> >> > > we can reuse it for a wider scope of needs.
>> >> > >
>> >> > >  --Sanne
>> >> > >
>> >> > > On 4 March 2013 17:02, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
>> >> > >>
>> >> > >>
>> >> > >> On 4 mars 2013, at 17:39, Sanne Grinovero <sanne at hibernate.org> wrote:
>> >> > >>
>> >> > >>> On 4 March 2013 16:20, Emmanuel Bernard <emmanuel at hibernate.org> wrote:
>> >> > >>>> I already gave what I knew on how to load an entity from a tuple (which
>> >> > >>>> isn't much) but we can try and dig together. Something I thought about
>> >> > >>>> is that ORM probably has a mechanism to load an entity from a resultset
>> >> > >>>> via the query parser. And that probably looks also like the second half
>> >> > >>>> of OgmLoader.load. We could look at this part and see if we can make an
>> >> > >>>> OGM version of it. We never had the need before as we never had query
>> >> > >>>> support (the way SQL does it).
>> >> > >>>
>> >> > >>> I would also need to study the ORM code, but to add a high level observation,
>> >> > >>> the methods currently defined by the GridDialect are focusing on
>> >> > >>> loading from well known key instances,
>> >> > >>> there is nothing to makes us able to scan/inspect for all values.
>> >> > >>>
>> >> > >>> In other words: even if we wanted to load keys first, we don't have definitions
>> >> > >>> of functions from raw->primary key instances either.
>> >> > >>
>> >> > >> I understand that. I'm not denying the need for the method.
>> >> > >>
>> >> > >>>
>> >> > >>>
>> >> > >>>> On the visitor vs Iterator approach, I still don't see how implementing
>> >> > >>>> an Iterator on a map / reduce backend would be harder than the visitor
>> >> > >>>> but maybe I'm missing something.
>> >> > >>>>
>> >> > >>>>    class IteratorAsStream {
>> >> > >>>>        final Query someMapReduceQuery = ...;
>> >> > >>>>
>> >> > >>>>        public Object next() {
>> >> > >>>>            if (!someMapReduceQuery.started()) {
>> >> > >>>>                // execute and collect results in parallel
>> >> > >>>>                someMapReduceQuery.execute();
>> >> > >>>>            }
>> >> > >>>>            Object result = someMapReduce.getNextOrBlock();
>> >> > >>>>            return result;
>> >> > >>>>        }
>> >> > >>>>    }
>> >> > >>>
>> >> > >>> That could work to *load* all entities in parallel, but I'd like to
>> >> > >>> process the entities in parallel as well.
>> >> > >>> And I'd rather not force the GridDialect implementors to write some
>> >> > >>> Hibernate Search specific code,
>> >> > >>> so to break out we need some form of "Execute X on each": a closure or a lambda.
>> >> > >>>
>> >> > >>
>> >> > >> I can't see how the visitor model helps in your processing of entities in parallel. To me both approaches are strictly equivalent. Care to show some pseudo-code?
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