Re: localObject vs prefetches: would there be a benefit ?

[Marcin Skladaniec]

Hi Mike



Marcin


On 02/11/2007, at 11:23 PM, Mike Kienenberger wrote:

Thats exactly what I mean: localObject is copying one object at the time. So say I have in my contextA 1 Gallery with 300 related Paintings, all with PersistentState.COMMITED. I do contextB.localObject on Gallery, then I access every Painting via relaionship. this means that the localObject will be invoked 301 times, everytime with single object. I believe this will be faster than re-fetching the data, but what if there will be 3000 Paintings ? Is there a limit after which the localObject becomes slower than re- fetch ?

I am no expert in this subject, but the cost of doing I/O is always
going to exceed the cost of in-system memory copies, probably by
orders of magnitude.   The only place where this might not be true is
using an in-memory database such as an HSQLDB mem jdbc connection.

So unless you're copying orders-of-magnitude more data than you'd be
fetching, always copy.

Remember too that a localObject only copies the object, not any of its
relationships.   And the other objects are only pulled in if you
access them, which is even more fine-grained than prefetching.

So my guess is that localObject is ALWAYS orders of magnitude faster.
I suspect it'd be extremely difficult to define a situation where this
was not the case.

On 11/1/07, Marcin Skladaniec <[EMAIL PROTECTED]> wrote:

Hi

We are improving the performance of our client application (ROP). Not
surprisingly we have found that adding prefetches did improve the
speed significantly.

I have a question though about which is about efficiency of

to a specific one non-editable context. If the object is to be edited
it has to be copied to another context which allows committing
changes. After the object is copied all the related object are
accessed, so the performance of the copying came to my mind.

The test I have looks like this:

CayenneContext context1;
CayenneContext context2;

SelectQuery q = new SelectQuery(Painting.class);
q.addPrefetch(Painting.GALLERY_PROPERTY);

List l = context1.performQuery(q);
//now the context1 contain all the records I wanted it to contain

Painting p1 = (Painting) l.get(0);


//now the context2 contain only the single record I copied
p2.getGallery().getCity();
//now  context2 contains the same objects as context1

All is very quick, but my question is how it will scale when the
relationship would be to-many and there will be hundreds related
records.


have to be localised over which it would be worth doing a new,
specific select query for that single object (with prefetches). Would
there be advantage of doing that at all ?

We are using cutting edge version of cayenne (I think we use build
about 2-3 weeks old).

Marcin

localObject. We are fetching a list of objects (query with prefetches) q.addPrefetch(Painting. GALLERY_PROPERTY + "." + Gallery.CITY_PROPERTY); Painting p2 = (Painting) context2.localObject(p1.getObjectId(), null); What do you think would be a threshold number of related objects which

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