[hibernate-dev] [OGM] Ogm mass indexer, how to convert Tuple/EntityKey to Entity/Id?
Emmanuel Bernard
emmanuel at hibernate.org
Tue Mar 5 12:44:53 EST 2013
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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