[hibernate-dev] Pooled Optimiser Improvements
Scott Marlow
smarlow at redhat.com
Tue Dec 15 20:15:49 EST 2015
https://github.com/scottmarlow/hibernate-orm/commits/pooledOptimizer_5.x
is looking more correct now, if others want to look at that.
On 12/15/2015 07:58 PM, Scott Marlow wrote:
>
>
> On 12/15/2015 05:58 PM, Scott Marlow wrote:
>>
>>
>> On 12/15/2015 05:40 PM, Scott Marlow wrote:
>>> I changed the new test methods a bit. [2] seems to be passed the tests
>>> but I am not understanding how PooledThreadLocalLoOptimizer should
>>> coordinate with the AccessCallback to allocate the next chunk of
>>> sequence numbers.
>>>
>>> We seem to be able to call AccessCallback.getNextValue() to get the next
>>> available sequence number but how do we reserve a block of 5000 sequence
>>> ids? Am I supposed to call callback.getNextValue() an extra time to get
>>> a range of values? Is there a separate database transaction that is
>>> used by the AccessCallback.getNextValue() calls? I'm missing something.
>>
>> Thinking more about this, I assume that AccessCallback.getNextValue() is
>> operating under a database transaction that we are probably ending
>> before AccessCallback.getNextValue() returns. It also sounds like the
>> database table is tracking the "lo" value, as mentioned in the
>> PooledLoOptimizer. This implies that only the application layer knows
>> what the range is. This seems like an important dependency to understand.
>>
>> Make sense?
>
> http://in.relation.to/2007/04/10/new-323-hibernate-identifier-generators
> seems to explain how increment_size is used. Since the user is already
> configured that, will look into switching to that for
> PooledThreadLocalLoOptimizer.
>
>>
>>>
>>> Note that [2] also includes a test change to comment out a few lines in
>>> SchemaUpdateDelimiterTest, due to the compiler error that I am seeing in
>>> intellij. Will need to remember to remove that change.
>>>
>>> [2]
>>> https://github.com/scottmarlow/hibernate-orm/commits/pooled-optimiser-hack-2
>>>
>>> On 12/15/2015 12:36 PM, Steve Ebersole wrote:
>>>> Those tests tend to assert the increments. We seem to agree that this
>>>> ThreadLocal one can skip gaps of values. I'd look there first.
>>>>
>>>>
>>>> On Tue, Dec 15, 2015 at 11:34 AM Scott Marlow <smarlow at redhat.com
>>>> <mailto:smarlow at redhat.com>> wrote:
>>>>
>>>> I'm trying to move the optimizer to PooledThreadLocalLoOptimizer [1].
>>>> We are currently failing some new unit tests, which are cloned from
>>>> existing PooledLoOptimizer tests which might be part of the problem.
>>>>
>>>> Scott
>>>>
>>>> [1]
>>>> https://github.com/scottmarlow/hibernate-orm/tree/pooled-optimiser-hack
>>>>
>>>> On 12/14/2015 10:12 PM, Scott Marlow wrote:
>>>> >
>>>> >
>>>> > On 12/11/2015 09:30 AM, Steve Ebersole wrote:
>>>> >> It's hard to say without understanding the scenario where you
>>>> are seeing
>>>> >> this as a problem. I have some guesses as to what may be the
>>>> problem,
>>>> >> but without understanding more about why you see this as a
>>>> problem in
>>>> >> the first place it is hard to give you an answer. For example,
>>>> I wonder
>>>> >> if for environments not using multi-tenancy whether the recent
>>>> changes
>>>> >> for the generators to support multi-tenancy might be the
>>>> culprit. If
>>>> >> that is the case, and those changes are in fact the underlying
>>>> cause of
>>>> >> the perf issues you see then I think there is actually a better
>>>> >> solution. But again, its hard to say unless we understand the
>>>> reason
>>>> >> this "shows up" as a perf problem for you.
>>>> >
>>>> > As best as I can tell from looking at the current PooledLoOptimizer,
>>>> > versus the proposed change (to have a chunk of ids per thread),
>>>> we went
>>>> > from accessing a contented lock, to instead using per thread memory
>>>> > (eliminating the contended lock on PooledLoOptimizer.generate()).
>>>> >
>>>> >>
>>>> >> Until we hear more I think at this stage I'd vote for a separate
>>>> >> optimizer. And maybe even not one that is upstream.
>>>> >>
>>>> >> Also I agree with Scott that I am VERY leery of not cleaning up a
>>>> >> ThreadLocal.
>>>> >
>>>> > My mistake, as Stuart pointed out, the TL is not static, so we
>>>> shouldn't
>>>> > introduce any leaks.
>>>> >
>>>> >>
>>>> >> On Fri, Dec 11, 2015 at 7:55 AM Scott Marlow <smarlow at redhat.com
>>>> <mailto:smarlow at redhat.com>
>>>> >> <mailto:smarlow at redhat.com <mailto:smarlow at redhat.com>>> wrote:
>>>> >>
>>>> >> Should this be a specialized pooled optimizer that is only
>>>> used in
>>>> >> environments that do not suffer from leaving the
>>>> ThreadLocal around
>>>> >> after the application is undeployed? In other words, the
>>>> expectation is
>>>> >> that classloader leaks with this pooled optimizer are
>>>> expected (e.g.
>>>> >> user must restart the jvm to really undeploy the application
>>>> >> completely).
>>>> >>
>>>> >> I am thinking that there are at least three typical situations:
>>>> >>
>>>> >> 1. Applications are deployed in Java standalone edition.
>>>> Generally,
>>>> >> when the app undeploys the jvm is shutting down.
>>>> >>
>>>> >> 2. Applications are deployed as part of some container
>>>> (e.g. an EE
>>>> >> server) and the Hibernate jars are on the global
>>>> classloader path (or
>>>> >> something like that). On each shared container thread,
>>>> there would be
>>>> >> one Optimizer for all deployed applications. I wonder if
>>>> instead, we
>>>> >> would want one Optimizer instance per Hibernate SessionFactory
>>>> >> associated with the many container threads?
>>>> >>
>>>> >> 3. Applications are deployed as part of some container
>>>> (e.g. an EE
>>>> >> server) and the Hibernate jars are deployed with the
>>>> application. The
>>>> >> ThreadLocals are associated with threads that are shared by
>>>> different
>>>> >> deployed applications. The application classloader contains the
>>>> >> Hibernate classes. Each deployed application has its own
>>>> Optimizer
>>>> >> threadlocal. On each shared container thread, there would
>>>> be one
>>>> >> Optimizer per application (since each application has its
>>>> Optimizer TL).
>>>> >> Like (2), there would be sharing of the same Optimizer
>>>> with the many
>>>> >> application session factories. Should we instead have an
>>>> optimizer per
>>>> >> session factory?
>>>> >>
>>>> >> Scott
>>>> >>
>>>> >> On 12/10/2015 11:31 PM, Stuart Douglas wrote:
>>>> >> > Hello,
>>>> >> >
>>>> >> > I have been working on a change to the pooled optimizer
>>>> that we
>>>> >> have been seeing good performance results with. Basically
>>>> it hands
>>>> >> out blocks of ID's to a thread local, rather than having every
>>>> >> thread contend on the lock every time an ID is required.
>>>> >> >
>>>> >> >
>>>> >>
>>>> https://github.com/hibernate/hibernate-orm/compare/master...stuartwdouglas:pooled-optimiser-hack
>>>> >> >
>>>> >> > What would I need to do to get a change like this in? In
>>>> particular:
>>>> >> >
>>>> >> > - Does it need to be a new type of optimizer, or is
>>>> modifying the
>>>> >> existing one like I have done OK?
>>>> >> > - How should it be configured?
>>>> >> >
>>>> >> > I am happy to do up a PR for this, but I am just not
>>>> really sure
>>>> >> what would be required to get it to a point where it would be
>>>> >> acceptable for inclusion.
>>>> >> >
>>>> >> > Stuart
>>>> >> > _______________________________________________
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