[hibernate-dev] Bytecode enhanced, Reference Cached immutable Entities
John O'Hara
johara at redhat.com
Fri Mar 27 07:42:24 EDT 2015
Steve,
From our point of view, we would not be looking to backport any
features introduced to any of the ORM4 releases. Our focus has shifted
to the next major release of EAP as we have a number of issues we need
to overcome. Getting this feature into ORM5 sooner rather than later is
essential for our use case in the future.
Thanks
John
On 27/03/15 11:36, Steve Ebersole wrote:
> BTW, if we go this route this *cannot* be backported because we do
> allow users to override EntityPersister; its an extension point.
> Adding a new method to extension points in bugfixes is a no-no.
>
> On Fri, Mar 27, 2015 at 6:35 AM, Steve Ebersole <steve at hibernate.org
> <mailto:steve at hibernate.org>> wrote:
>
> An EntityPersister describes each entity you defined in your
> model. Its one-to-one between @Entity and EntityPersister. And
> really, it is totally reasonable to have the EntityPersister
> determine the "EntityEntry builder" to use. That also eliminates
> needing to develop yet-another-extension-point because if we
> expose it from EntityPersister OGM already swaps EntityPersister
> impls so this would JustWork.
>
> On Fri, Mar 27, 2015 at 6:04 AM, John O'Hara <johara at redhat.com
> <mailto:johara at redhat.com>> wrote:
>
> On 26/03/15 16:22, Steve Ebersole wrote:
>> The contract I suggested btw is missing one use case I know
>> we have discussed in regards to OGM a few times... the
>> ability to store references to datastore specific locators (I
>> think the use case was to efficiently load collections
>> through that datastore reference). But that (obviously)
>> requires passing extra, specific state into
>> the createEntityEntry method. Not really sure the best way
>> to handle such things tbh.
>>
> If we did have a "creation Context" parameter passed to the
> createEntityEntry, we would be instantiating more objects,
> however if we went with Sanne' suggestion if caching the
> EnityEntryFactory with the EntityPersister, how many objects
> would be actually created? I am not sure about the
> relationship between Entity, EntityEntry and Session but could
> this a possibility if there is a 1-1 relationship between
> EntityPersister and no. of different Entities definitions?
>
>
>> On Thu, Mar 26, 2015 at 11:16 AM, Steve Ebersole
>> <steve at hibernate.org <mailto:steve at hibernate.org>> wrote:
>>
>> Apparently I hit some key combo that means send :) To
>> finish up...
>>
>> On Thu, Mar 26, 2015 at 10:58 AM, Steve Ebersole
>> <steve at hibernate.org <mailto:steve at hibernate.org>> wrote:
>>
>>
>> On Thu, Mar 26, 2015 at 10:20 AM, Sanne Grinovero
>> <sanne at hibernate.org <mailto:sanne at hibernate.org>> wrote:
>>
>>
>> Concurrency
>> Since the goal is to share the
>> ImmutableEntityEntry instance among
>> multiple threads reading it, I'd rather make sure
>> that it is really
>> immutable. For example it now holds onto
>> potentially lazy initialized
>> fields, such as getEntityKey().
>> If it's not possible to make it really immutable
>> (all final fields),
>> we'll need to make it threadsafe and question the
>> name I'm proposing.
>>
>>
>> The specific use-case John is interested in does
>> indeed need to be completely thread-safe and fully
>> concurrent.
>>
>>
>> LockMode
>> From a logical perspective of users, one might
>> think that an entity
>> being "immutable" doesn't necessarily imply I
>> can't lock on it..
>> right? I'm not sure how far it could be a valid
>> use case, but these
>> patches are implying that one can't lock an
>> immutable entity anymore,
>> as the lock state would be as immutable as
>> anything else on the
>> EntityEntry.
>> Are we good with that? Alternatively one might
>> need to think to
>> separate the lock state handling from the
>> EntityEntry.
>>
>>
>> Conceptually there is nothing wrong with requesting a
>> READ lock on an immutable entity. But like you said,
>> what is the logical expectation there? IMO there
>> should be none. But if we decide that it is OK to req
>>
>> But if we decide that it is OK to request a lock on an
>> immutable entity, that is problematic for the idea of a
>> "SharedEntityEntry" or an "ImmutableEntityEntry" because
>> a lock is associated with a Session which is what the
>> EntityEntry is meant to model... an entity's information
>> in relation to a Session. Aka, it now needs to hold state.
>>
>>
>>
>> Notice I said immutable here and not READ_ONLY which
>> is a specific distinction which is important to other
>> parts of your email that I will address in a second
>> email.
>>
>>
>> On smaller details:
>> # org.hibernate.engine.internal.SharedEntityEntry
>> is hosted in an
>> .internal package, I don't think it's right to
>> refactor all the public
>> API javadoc which was referring to EntityEntry to
>> now refer to the
>> internal implementation.
>> # things like EntityEntryExtraState should
>> probably get moved to
>> .internal packages as well now - we couldn't do
>> that before without
>> breaking either encapsulation or APIs.
>>
>>
>> +1
>>
>>
>> In terms of git patches, the complexity of the
>> changeset risks to get
>> a bit our of hand. What about we focus on
>> creating a clean pull
>> request which focuses exclusively on making
>> EntityEntry an interface,
>> and move things to the right packages and javadoc?
>>
>>
>> Agree 100%
>>
>> You'd have a trivial EntitEntryFactory, and we
>> can then build the
>> evolution on top of that, not least maybe helping
>> out by challenging
>> some points in parallel work.
>> These are the things I'd leave for a second
>> iteration:
>> - add various implementations of EntityEntry
>> iteratively, as needed
>> - the strategy such a Factory would use the pick
>> an implementation
>> - ultimately, make it possible for an integrator
>> to override such a Factory
>>
>>
>> This all seems reasonable. For 5.0 I think the most
>> important thing is to nail down the idea of EntityEntry
>> as an interface, introduce a Factory for building them
>> and agree on the signature for building them. Granted we
>> may need iteration to finalize the actual Factory
>> signature, especially as OGM finally starts to use it,
>> but I think that in general we can get it pretty close.
>> Worst case we just pass high-level constructs like the
>> EntityPersister (which OGM supplies custom impls) and the
>> Session and all the "EntityEntry state". For the purpose
>> of starting a discussion:
>>
>> public interface EntityEntryFactory {
>> public EntityEntry createEntityEntry(
>> PersistenceContext persistenceContext,
>> EntityPersister persister,
>> Status status,
>> Serializable id,
>> Object version,
>> Object[] loadedState,
>> Object rowId,
>> LockMode lockMode,
>> boolean existsInDatabase,
>> boolean disableVersionIncrement,
>> boolean lazyPropertiesAreUnfetched);
>> }
>>
>> I would suggest a "creation context" method param object
>> to pass in here, but seeing as how we are trying to stop
>> instantiations...
>>
>> I would prefer the definition of the EntityEntryFactory
>> to use be defined via SessionFactoryBuilder interface. I
>> already have plans to have a auto-loaded hook for
>> integrators to be able to adjust the
>> SessionFactoryBuilder. But as a Service is fine too.
>>
>>
>> For example with Hibernate OGM we might want to
>> override / re
>> configure the factories to use custom EntityEntry
>> implementations -
>> requirements are not fully clear at this point
>> but it seems likely.
>>
>> The priority being to define the API as that
>> would be a blocker for
>> 5.0, we have then better choices to leave more
>> smarter and advanced
>> EntityEntry implementations for the future; we'd
>> still need to
>> implement at least the essential ones to make
>> sure the API of the
>> EntityEntryFactory has all the context it needs.
>>
>> Thanks,
>> Sanne
>>
>>
>> On 24 March 2015 at 09:27, John O'Hara
>> <johara at redhat.com <mailto:johara at redhat.com>> wrote:
>> > Steve,
>> >
>> > Have you had chance to look at this? Do you
>> have any comments/observations?
>> >
>> > Thanks
>> >
>> > John
>> >
>> >
>> > On 17/03/15 09:24, John O'Hara wrote:
>> >
>> > Steve,
>> >
>> > I have been having a think about the
>> EntityEntry interface, and have forked
>> > a branch here:
>> >
>> >
>> https://github.com/johnaoahra80/hibernate-orm/tree/EntityEntryInterface
>> >
>> > I know it is nowhere near complete, but was
>> this the sort of idea you had in
>> > mind?
>> >
>> > Thanks
>> >
>> > John
>> >
>> >
>> > On 13/03/15 09:44, John O'Hara wrote:
>> >
>> > EntityEntry retains a reference to a
>> persistenceContext internally that
>> >
>> org.hibernate.engine.spi.EntityEntry#setReadOnly
>> makes calls to, is this
>> > where the session reference is kept? As
>> > org.hibernate.engine.spi.PersistenceConext is
>> an interface could we have a
>> > different implementation for this use case? e.g. an
>> > ImmutablePersistenceContext that could be
>> shared across sessions?
>> >
>> > For the bytecode enhancement, could we change
>> the enhancer so that it adds
>> > an EntityEntry interface with javassist.
>> > ClassPool.javassist.ClassPool.makeInterface()()
>> as opposed to adding a class
>> > javassist.ClassPool.makeClass()? I need to have
>> a look at javassit to
>> > confirm what
>> javassist.ClassPool.makeInterface() does.
>> >
>> > Thanks
>> >
>> > John
>> >
>> > On 12/03/15 18:52, Steve Ebersole wrote:
>> >
>> > It is possible. Although some of the changes
>> are particularly painful.
>> > Most of EntityEntry, if it is an interface, can
>> be made to work with your
>> > use case.
>> org.hibernate.engine.spi.EntityEntry#setReadOnly
>> I think is the
>> > one exception, because:
>> > 1) your use case needs it
>> > 2) it expects the Session to be available
>> internally (its not passed)
>> >
>> > The bigger thing I am worried about for you is
>> the bytecode stuff, as that
>> > ties very tightly with EntityEntry.
>> >
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>>
>>
>>
>
>
> --
> John O'Hara
> johara at redhat.com <mailto:johara at redhat.com>
>
> JBoss, by Red Hat
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>
>
--
John O'Hara
johara at redhat.com
JBoss, by Red Hat
Registered Address: Red Hat UK Ltd, Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SI4 1TE, United Kingdom.
Registered in UK and Wales under Company Registration No. 3798903 Directors: Michael Cunningham (USA), Charlie Peters (USA), Matt Parsons (USA) and Michael O'Neill (Ireland).
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