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)
+
+}

app/com/ysoft/debug/ObjectGraphDuplicityMeasurer.scala

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+package com.ysoft.debug
+
+import java.util
+
+import com.google.caliper.memory.ObjectVisitor.Traversal
+import com.google.caliper.memory.{Chain, ObjectExplorer, ObjectVisitor}
+
+import scala.collection.mutable
+
+object ObjectGraphDuplicityMeasurer {
+
+  def measureUnique(obj: AnyRef) = {
+    ObjectExplorer.exploreObject(obj, new ObjectVisitor[((Int, Int), Map[Class[_], (Int, Int)])](){
+      val all = KnownObjects(
+        objSet = new util.HashSet[Any](),
+        identitiesSet = java.util.Collections.newSetFromMap(new util.IdentityHashMap[Any, java.lang.Boolean]())
+      )
+
+      val classMap = mutable.Map[Class[_], KnownObjects]()
+      def forClass(cl: Class[_]) = classMap.contains(cl) match{
+        case true => classMap(cl)
+        case false =>
+          val kn = KnownObjects()
+          classMap(cl) = kn
+          kn
+      }
+
+      override def visit(chain: Chain): Traversal = {
+        val value = chain.getValue
+        if(chain.isPrimitive || value == null || classOf[Enum[_]].isAssignableFrom(chain.getValueType) || value.isInstanceOf[Class[_]] ){
+          Traversal.SKIP
+        }else{
+          val res = all.visit(value)
+          forClass(value.getClass).visit(value)
+          res
+        }
+      }
+
+      override def result() = (all.stats, classMap.toMap.mapValues(_.stats).map(identity))
+
+    })
+  }
+
+}