[hibernate-dev] Why hibernate-jcache is not enough (for Infinispan)
Radim Vansa
rvansa at redhat.com
Tue Apr 3 06:13:45 EDT 2018
On 03/29/2018 02:11 PM, Steve Ebersole wrote:
> Thanks for the thoughts Radim.
>
> But I think that there is a misunderstanding..
>
> Today (pre-5.3) Hibernate has a hibernate-infinispan module that
> integrates Infinispan into Hibernate ORM as a second-level cache. In
> fact it provides 2 integrations: `InfinispanRegionFactory` and
> `JndiInfinispanRegionFactory`. And then inside WildFly there is (at
> least) a third one specific to running inside WildFly. Inside WildFly
> is irrelevant... I say that because inside WildFly we are going to use
> whatever the Infinispan team develops as infinispan-hibernate-cache.
> Which leaves the other 2. The only thing (I believe) that
> `InfinispanRegionFactory` and `JndiInfinispanRegionFactory` provide
> over (and actually in any way different from) hibernate-jcache is
> transactional access support, which you even say is going away.
>
> I understand about not being able to fully leverage
> `CacheTransactionSynchronization` if hibernate-jcache is used. IMO it
> is the single drawback to using hibernate-jcache for Infinispan. All
> of the other things you mentioned are IMO implementation details.
> Well that and missing out on the new `DomainDataRegionConfig` stuff.
> And keep in mind that even hibernate-jcache offers some integration
> points (thanks to Alex)... you can supply your own
> `javax.cache.spi.CachingProvider` or `javax.cache.CacheManager`
> directly to the RegionFactory for JCache. So you have total control
> still over how caches are built (sans access to `DomainDataRegionConfig`).
>
> So all-in-all I am still not understanding why `hibernate-jcache` +
> `infinispan` is not enough for most cases. Yes you miss out on some
> possible performance improvements (leveraging
> `CacheTransactionSynchronization` and `DomainDataRegionConfig` being
> the 2 I can think of).
Maybe I understand what hibernate-jcache is incorrectly. Infinispan
exposes JCache API, and JCache dictates some behaviour. The behaviour
with transactions is not specified and not tested by the JCache TCK.
Hibernate-jcache consumes JCache API. I don't see any space for
'integration' besides dropping some configuration files (and that's the
point, no code to maintain).
My post was about the behaviour that can be optimized once we know the
intent. JCache API is implemented according to the spec and does not
express Hibernate's intent well enough.
> However, that's why there is the possibility of a custom cache
> provider - to leverage those things. But again, taking a step back
> and looking at the big picture...
>
> 1) We need to be able to run outside of WildFly. The 2 legacy
> `hibernate-infinispan` providers were intended for that.
> 2) We need to be able to run inside of WildFly. The provider supplied
> with WildFly (Jipijapa) itself was intended for that.
>
> So how do we do that moving to 5.3? As I mentioned above, I think we
> can ignore "run inside of WildFly" for this discussion - that will
> happen however Jipijapa says it will happen; if/when there is a
> specific Infinispan-based 5.3 cache provider, Jipijapa will use that.
> It's more the "run outside of WildFly" case that I am talking about.
> So what are the things that we want to cover in Hibernate/Infinispan
> caching combo? AFAIK:
>
> 1. Transactional access support
> 2. Cluster support (distributed versus replicated versus invalidated)
> 3. Anything I am missing?
>
> So let's look at those 1-1:
>
> 1. You just said that you plan to drop transactional acccess support
> anyway, so nothing to see here...
>
I've never said that I am dropping support for transactional *access*!
org.hibernate.cache.spi.access.AccessType.TRANSACTIONAL will be always
supported. We're dropping support for transactional *caches*.
> 1. I may be wrong here, but I do not think that hibernate-infinispan
> supported clustering (or at least very well) out-of-the-box. At
> least not based on the top google hits I saw for "hibernate
> infinispan cluster".
>
Clustered support is default, you need to specify non-clustered
configuration file via property if you don't want that one.
> Given these points and the fact that Infinispan can (and would already
> have to) implement JCache's `CachingProvider` / `CacheManager`, I
> simply do not buy that `hibernate-jcache` + `infinispan` is any less
> capable than the support we have today for Infinispan as a second
> level cache. Now, if you say that you want to develop a 5.3 provider
> to actually make cluster setup easier, leverage
> `CacheTransactionSynchronization` and/or other specific reasons....
> great, that is completely your prerogative and the reason this is all
> still pluggable.
>
> P.S. JTA is a spec. JTA components are accessible from a "well known
> location" (aka, easily accessible by anyone). So I really just do not
> get your argument that `hibernate-jcache` + `infinispan` somehow loses
> the ability to leverage JTA. And btw this was absolutely not the
> intent with `CacheTransactionSynchronization`, which was instead
> intended to allow unified processing of "cache events" at the "end of
> a transaction" (as known to Hibernate) regardless of whether JTA or
> straight JDBC transactions are used.
I have complained about JCache + JTA being undefined, nothing about
leveraging JTA in our impl.
>
> P.S.S. I totally agree with Sanne. The cache should be as correct as
> possible, however it is *always* possible to simply evict a piece of
> data from the cache to avoid conflicts. The database is *always* the
> "truth of the system". This in in fact exactly the principle that the
> collection cache works - any changes to that collection simply
> invalidate (evict) the data from the cache.
When you simply evict a piece of data from the cache you can't be sure
that that piece won't end up in there right away because another
concurrent request holding stale data hits the cache again.
R.
>
>
> On Thu, Mar 29, 2018 at 3:03 AM Radim Vansa <rvansa at redhat.com
> <mailto:rvansa at redhat.com>> wrote:
>
> Hi Steve,
>
> on HipChat you've asked why hibernate-jcache + Infinispan's
> implementation of JCache is not enough. It ultimately boils down to
>
> 1. performance
> 2. correctness
>
> where (2) can be fine with some providers but then (1) suffers.
> Infinispan offers transactional mode, but it's not serializable (gosh,
> sometimes it's even read_uncommitted) and has its quirks. The
> performance can't be as good as with non-tx mode, too. That's why the
> native transactional caches support will be dropped in 5.3 and we'll
> just emit a warning to update their configuration (and continue with
> non-tx config).
>
> As a demonstration of this we can use the putFromLoad. If you
> implement
> this as a (ideal serializable) transactional cache putIfAbsent, the
> provider must either
> a) lock the key (pessimistic approach) - but we don't want to block
> other nodes removing data from the cache (on write) or putFromLoading
> (on read!)
> b) resolve conflicts when the transaction is committing: you
> figure out
> that there are two concurrent updates and rollback one of the
> transactions - that's not acceptable to us either, as any failure in
> cache should not affect DB transaction. And there's a risk of blocking
> between the 2 phases of commit, too.
>
> Theoretically you could just wipe any modified data on conflict - I
> don't know if anyone does that, 'drop everything and proceed with
> commit' is not something I'd expect from a general-purpose (NoSQL)
> DB. I
> recall Alex's JCache implementation (for 5.2) storing some 'lock'
> objects in the cache, and you probably don't want to wipe those.
>
> Interaction with evictAll/removeAll could be also problematic: not
> sure
> about the other providers but Infinispan's clear() operation is
> non-transactional even on tx cache (since Infinispan 7 or so) because
> it's impractical to resolve all conflicts. I don't know details how
> others provide that operation but there may be a hidden problem.
>
> Last but not least, you assume that the provider is transactional
> and it
> provides JCache interface. JCache does not define interaction with
> JTA,
> because it was hard to get agreement on non-tx behaviour (why did it
> take 13 years to complete the JSR?) and it would be even harder
> for JTA.
> So what you expect is just your extrapolation or wishful thinking, and
> it's up to integrators to verify that the unwritten contract is
> fulfilled within the scope of hibernate-jcache module use. Not
> that SPI
> implementors would be in a better position, but at least we are aware
> that (for us) it's not enough to implement those 3 classes and
> job's done.
>
> Of course the correctness aspect may be ignored with 'it's just a
> cache'
> implying 'users expect stale/uncommitted data' as Sanne (who is much
> closer to the customers than me) keeps repeating. However this is not
> what 2LC promises as I understand it: the same results as DB would do.
>
> I am really grateful that in 5.3 you've provided the
> CacheTransactionSynchronization that will help us boost (1) even
> further
> by allowing us to execute all operations in parallel. And it's
> good that
> you've made the SPI more expressive with the intent; there'll be a
> bunch
> of TODOs in the 5.3 implementation to cover use cases that were not
> handled in previous versions but now are obvious.
>
> Cheers
>
> Radim
>
> --
> Radim Vansa <rvansa at redhat.com <mailto:rvansa at redhat.com>>
> JBoss Performance Team
>
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--
Radim Vansa <rvansa at redhat.com>
JBoss Performance Team
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