[hibernate-dev] Bytecode interception and attribute name versus attribute index

[Steve Ebersole]

I have no estimate as to how much this would help.  Many of the
improvements coming from the performance work have been of the sort that is
removing Map lookups; some of them across VERY small (and finite) sets of
Map keys.  My concern here is that the Map look up occurs any time an
enhanced entity's getter or setter is called, which seems like a
potentially bigger performance impact.

I'm going to table this for now until the jandex-binding work.  But as part
of that work, I think it makes a ton of sense to make sure we develop a
strategy for consistent ordering of processing attributes.

On Thu, Nov 12, 2015 at 2:36 AM Gunnar Morling <gunnar at hibernate.org> wrote:

> Is there any estimate what would be gained perf-wise by doing this
> optimization?
>
> > First, this obviously is more fragile than relying on names; if the order
> > changes but the bytecode is not re-enhanced, that could lead to very
> > subtle, nasty problems.
>
> Agreed, but to me it seems acceptable with such optimization having to
> be explicitly enabled and the docs of that setting describing this
> matter clearly.
>
> > The other issue is that this requires us to be able to consistently be
> able
> > to order the attributes.
>
> Maybe the enhancer could enhance entities with a (static) method
> returning the attribute order it works with, or maybe some separate
> contract for making this order available. Then at runtime this order
> could be fed to persisters et al. for enhanced entities.
>
> Not sure whether it's doable or how complex it'd be, just throwing out the
> idea.
>
> --Gunnar
>
>
> 2015-11-11 21:37 GMT+01:00 Steve Ebersole <steve at hibernate.org>:
> > As I work on HHH-10267, a thought that keeps coming up in my head is that
> > it would be great to avoid Map lookups in the enhancement and
> interception
> > code.
> >
> > As an example of what I mean, consider the reader for a String field
> named
> > `name` which roughly looks like:
> >
> > public String $$_hibernate_read_name() {
> >     return (String) $$_hibernate_getInterceptor().readObject( this,
> "name",
> > this.name );
> > }
> >
> > In the interception code we need to resolve the attribute name ("name"
> > above) to the pertinent information from the persister,etc.  Typically
> this
> > is a Map lookup; sometimes it is a done by iterating a String[] of the
> > attribute names.
> >
> > Ultimately the information is taken from persister and friends, which
> means
> > that the information is generally already readily consumable via array
> > access once we have resolved the name to a proper index.  Which got me
> > thinking it would be great if we could encode the attribute index into
> the
> > enhanced entity directly.  Going back to the example about.. if we knew
> > that the "name" attribute was the 4th attribute (index=3) according to
> the
> > entity persister we could leverage that information for better performing
> > access to the attribute metadata in the enhanced code and interceptor:
> >
> > public String $$_hibernate_read_name() {
> >     return (String) $$_hibernate_getInterceptor().readObject( this, 3,
> > this.name );
> > }
> >
> > One gotcha - always has to be one devil right ;)  Ok, 2 really...
> >
> > First, this obviously is more fragile than relying on names; if the order
> > changes but the bytecode is not re-enhanced, that could lead to very
> > subtle, nasty problems.
> >
> > The other issue is that this requires us to be able to consistently be
> able
> > to order the attributes.  The Enhancer currently does not rely on the
> built
> > metadata (org.hibernate.mapping) at all; it parses the entity annotations
> > (completely annotation specific) on its own.  Given the 2-phase break
> down
> > in JPA bootstrapping, having Enhancer leverage the built metadata is not
> > really going to be possible.  Which is unfortunate, because doing so
> would
> > be nice for other reasons (like supporting XML mappings for enhancement
> as
> > well, etc).
> >
> > That's a lot of information, sorry about that :)
> >
> > But anyone have thoughts on that?
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