Drastically reduced memory usage, mostly using deduplication.

app/com/ysoft/debug/KnownObjects.scala

@@ -0,0 +1,25 @@
+package com.ysoft.debug
+
+import java.util
+
+import com.google.caliper.memory.ObjectVisitor.Traversal
+import play.api.Logger
+
+// We use Java collections because they can have the initial size configured
+case class KnownObjects(
+  objSet: java.util.HashSet[Any] = new util.HashSet[Any](),
+  identitiesSet: java.util.Set[Any] = java.util.Collections.newSetFromMap(new util.IdentityHashMap[Any, java.lang.Boolean]())
+){
+  def visit(obj: AnyRef) = {
+    val seen = !identitiesSet.add(obj)
+    if(seen){
+      Traversal.SKIP
+    }else{
+      objSet.add(obj)
+      Traversal.EXPLORE
+    }
+  }
+
+  def stats = (identitiesSet.size, objSet.size)
+
+}