diff --git a/core/src/main/java/com/taobao/arthas/core/util/ThreadLocalWatch.java b/core/src/main/java/com/taobao/arthas/core/util/ThreadLocalWatch.java
index 2677863e0..9a5e1e257 100644
--- a/core/src/main/java/com/taobao/arthas/core/util/ThreadLocalWatch.java
+++ b/core/src/main/java/com/taobao/arthas/core/util/ThreadLocalWatch.java
@@ -1,18 +1,17 @@
 package com.taobao.arthas.core.util;
 
-import java.util.Stack;
-
 /**
  * 简单的调用计时器。
- * Created by vlinux on 16/6/1.
+ * 
+ * @author vlinux 16/6/1.
  * @author hengyunabc 2016-10-31
  */
 public class ThreadLocalWatch {
 
-    private final ThreadLocal<Stack<Long>> timestampRef = new ThreadLocal<Stack<Long>>() {
+    private final ThreadLocal<LongStack> timestampRef = new ThreadLocal<LongStack>() {
         @Override
-        protected Stack<Long> initialValue() {
-            return new Stack<Long>();
+        protected LongStack initialValue() {
+            return new LongStack(1024 * 4);
         }
     };
 
@@ -30,8 +29,52 @@ public class ThreadLocalWatch {
         return (System.nanoTime() - timestampRef.get().pop()) / 1000000.0;
     }
 
-    public void clear() {
-        timestampRef.remove();
-    }
+    /**
+     * 
+     * <pre>
+     * 一个特殊的stack，为了追求效率，避免扩容。
+     * 因为这个stack的push/pop 并不一定成对调用，比如可能push执行了，但是后面的流程被中断了，pop没有被执行。
+     * 如果不固定大小，一直增长的话，极端情况下可能应用有内存问题。
+     * 如果到达容量，pos会重置，循环存储数据。所以使用这个Stack如果在极端情况下统计的数据会不准确，只用于monitor/watch等命令的计时。
+     * 
+     * </pre>
+     * 
+     * @author hengyunabc 2019-11-20
+     *
+     */
+    static class LongStack {
+        private long[] array;
+        private int pos = 0;
+        private int cap;
 
+        public LongStack(int maxSize) {
+            array = new long[maxSize];
+            cap = array.length;
+        }
+
+        public int size() {
+            return pos;
+        }
+
+        public void push(long value) {
+            if (pos < cap) {
+                array[pos++] = value;
+            } else {
+                // if array is full, reset pos
+                pos = 0;
+                array[pos++] = value;
+            }
+        }
+
+        public long pop() {
+            if (pos > 0) {
+                pos--;
+                return array[pos];
+            } else {
+                pos = cap;
+                pos--;
+                return array[pos];
+            }
+        }
+    }
 }
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