On Jun 20, 2008, at 10:45 AM, Øyvind Harboe wrote:
1. Consider the code below. Will all the objects from the query
be locked in memory?
query=new SelectQuery(Foo.class);
query.setPageSize(1000); /* does this matter? */
/* Does performQuery return a clever implementation of
a List that does not lock the CayenneDataObjects into memory?
*/
l=context.performQuery(query);
while (i.hasNext())
{
Foo f=(Foo) i.next();
.... do some processing here that ...
}
2. When does peak memory usage occur above?
At the end of the the iterator when all pages are resolved.
3. Can a CayenneDataObject be garbage collected as long as it's
DataContext is in scope?
I'm wondering because as far as I have understood the two if
statements below are equivalent when a & b are CayenneDataObjects
in the same DataContext.
It is stored using a weak reference, so yes, it can be garbage
collected if there are no other references to the object in the code.
That is if 'a' can be garbage collected during the lifetime of the
DataContext, then 'a' is points to different objects during the
lifetime of CayenneDataObject's and a==b just 'barely' works.
Not "barely". It always works. If you have var "a" pointing to a given
object, that fact alone will prevent garbage collection within the
scope of "a" definition.
4. Should I consider some "clever" implementation of a query that
ensures that only a small amount of CayenneDataObject's are
locked in memory at the time?
Some ideas:
- use performIteratedQuery() w/setPageSize()
- ResultIterator.nextDataRow() is a bit strange: it returns a Map<>,
but
perhaps I can safely upcast that.
- use objectFromdataRow()
Yes, use 'performIteratedQuery' - it was designed for serial
processing of arbitrary size lists.
Andrus
