java heap analysis with oql: Count unique strings

Question

Im doing a memory analysis of an existing java software. Is there a sql \'group by\' equivalent in oql to see the count of objects with same values but different instances.<

Answer 1

Just post my solution and experience when doing similar issue for other references.

var counts = {};
var alreadyReturned = {};
top(
filter(
    sort(
        map(heap.objects("java.lang.ref.Finalizer"),
            function (fobject) {
                var className = classof(fobject.referent)
                if (!counts[className]) {
                    counts[className] = 1;
                } else {
                    counts[className] = counts[className] + 1;
                }
                return {string: className, count: counts[className]};
            }),
        'rhs.count-lhs.count'),
    function (countObject) {
        if (!alreadyReturned[countObject.string]) {
            alreadyReturned[countObject.string] = true;
            return true;
        } else {
            return false;
        }
    }),
    "rhs.count > lhs.count", 10);

The previous code will output the top 10 classes used by java.lang.ref.Finalizer.
Tips:
1. The sort function by using function XXX is NOT working on my Mac OS.
2. The classof function can return the class of the referent. (I tried to use fobject.referent.toString() -> this returned a lot of org.netbeans.lib.profiler.heap.InstanceDump. This also wasted a lot of my time).