diff --git a/logstash-core/lib/logstash/util/wrapped_acked_queue.rb b/logstash-core/lib/logstash/util/wrapped_acked_queue.rb
index b9892df3a..61546f547 100644
--- a/logstash-core/lib/logstash/util/wrapped_acked_queue.rb
+++ b/logstash-core/lib/logstash/util/wrapped_acked_queue.rb
@@ -253,7 +253,7 @@ module LogStash; module Util
 
         @generated = Hash.new
         @iterating_temp = Hash.new
-        @iterating = false # Atomic Boolean maybe? Although batches are not shared across threads
+        @is_iterating = false # Atomic Boolean maybe? Although batches are not shared across threads
         @acked_batch = nil
       end
 
@@ -274,7 +274,7 @@ module LogStash; module Util
         return if event.nil? || @originals.key?(event)
         # take care not to cause @generated to change during iteration
         # @iterating_temp is merged after the iteration
-        if iterating?
+        if @is_iterating
           @iterating_temp[event] = true
         else
           # the periodic flush could generate events outside of an each iteration
@@ -293,14 +293,14 @@ module LogStash; module Util
 
         # below the checks for @cancelled.include?(e) have been replaced by e.cancelled?
         # TODO: for https://github.com/elastic/logstash/issues/6055 = will have to properly refactor
-        @iterating = true
+        @is_iterating = true
         @originals.each do |e, _|
           blk.call(e) unless e.cancelled?
         end
         @generated.each do |e, _|
           blk.call(e) unless e.cancelled?
         end
-        @iterating = false
+        @is_iterating = false
         update_generated
       end
 
@@ -332,10 +332,6 @@ module LogStash; module Util
 
       private
 
-      def iterating?
-        @iterating
-      end
-
       def update_generated
         @generated.update(@iterating_temp)
         @iterating_temp.clear
diff --git a/logstash-core/lib/logstash/util/wrapped_synchronous_queue.rb b/logstash-core/lib/logstash/util/wrapped_synchronous_queue.rb
index 676d47e69..706149f34 100644
--- a/logstash-core/lib/logstash/util/wrapped_synchronous_queue.rb
+++ b/logstash-core/lib/logstash/util/wrapped_synchronous_queue.rb
@@ -3,8 +3,8 @@
 module LogStash; module Util
   class WrappedSynchronousQueue
     java_import java.util.concurrent.ArrayBlockingQueue
-    java_import java.util.concurrent.SynchronousQueue
     java_import java.util.concurrent.TimeUnit
+    java_import java.util.HashSet
 
     def initialize (size)
       @queue = ArrayBlockingQueue.new(size)
@@ -177,10 +177,8 @@ module LogStash; module Util
         # @cancelled = Hash.new
 
         #Sizing HashSet to size/load_factor to ensure no rehashing
-        @originals = java.util.HashSet.new(size * 4 / 3 + 1, 0.75)
-        @generated = Hash.new
-        @iterating_temp = Hash.new
-        @iterating = false # Atomic Boolean maybe? Although batches are not shared across threads
+        @originals = HashSet.new(size * 4 / 3 + 1, 0.75)
+        @is_iterating = false # Atomic Boolean maybe? Although batches are not shared across threads
         @acked_batch = nil
       end
 
@@ -199,11 +197,12 @@ module LogStash; module Util
         return if event.nil? || @originals.contains(event)
         # take care not to cause @generated to change during iteration
         # @iterating_temp is merged after the iteration
-        if iterating?
-          @iterating_temp[event] = true
+        if @is_iterating
+          @iterating_temp = HashSet.new if @iterating_temp.nil?
+          @iterating_temp.add(event)
         else
           # the periodic flush could generate events outside of an each iteration
-          @generated[event] = true
+          @originals.add(event)
         end
       end
 
@@ -215,33 +214,23 @@ module LogStash; module Util
 
       def each(&blk)
         # take care not to cause @originals or @generated to change during iteration
-        @iterating = true
+        @is_iterating = true
 
         # below the checks for @cancelled.include?(e) have been replaced by e.cancelled?
         # TODO: for https://github.com/elastic/logstash/issues/6055 = will have to properly refactor
         @originals.each do |e|
           blk.call(e) unless e.cancelled?
         end
-        
-        @generated.each do |e, _|
-          blk.call(e) unless e.cancelled?
-        end
-        @iterating = false
-        update_generated
-      end
-
-      def size
-        filtered_size
-      end
-
-      def starting_size
-        @originals.size
+        @is_iterating = false
+        update_generated unless @iterating_temp.nil?
       end
 
       def filtered_size
-        @originals.size + @generated.size
+        @originals.size
       end
 
+      alias_method(:size, :filtered_size)
+
       def cancelled_size
       # TODO: disabled for https://github.com/elastic/logstash/issues/6055 = will have to properly refactor
       raise("cancelled_size is unsupported ")
@@ -250,13 +239,11 @@ module LogStash; module Util
 
       private
 
-      def iterating?
-        @iterating
-      end
-
       def update_generated
-        @generated.update(@iterating_temp)
-        @iterating_temp.clear
+        @originals.add_all(@iterating_temp)
+        # Iterating Temp will not be used again in the lifecycle of the batch so we
+        # give a hint to the garbage collector here
+        @iterating_temp = nil
       end
     end