diff --git a/deps/oblib/src/lib/hash/ob_hashmap.h b/deps/oblib/src/lib/hash/ob_hashmap.h
index ceca6b00c0..f7ce51459d 100644
--- a/deps/oblib/src/lib/hash/ob_hashmap.h
+++ b/deps/oblib/src/lib/hash/ob_hashmap.h
@@ -147,13 +147,11 @@ public:
   int destroy()
   {
     int ret = ht_.destroy();
-    allocer_.clear();
     return ret;
   };
   int clear()
   {
     int ret = ht_.clear();
-    //allocer_.clear();
     return ret;
   };
   int reuse()
diff --git a/deps/oblib/src/lib/hash/ob_hashset.h b/deps/oblib/src/lib/hash/ob_hashset.h
index c77606f6fd..87830a6964 100644
--- a/deps/oblib/src/lib/hash/ob_hashset.h
+++ b/deps/oblib/src/lib/hash/ob_hashset.h
@@ -114,7 +114,6 @@ public:
   {
     // ret should be handle by caller.
     int ret = ht_.destroy();
-    allocer_.clear();
     return ret;
   }
   int clear()
diff --git a/deps/oblib/src/lib/hash/ob_hashtable.h b/deps/oblib/src/lib/hash/ob_hashtable.h
index d8a79a6dd2..2659efd394 100644
--- a/deps/oblib/src/lib/hash/ob_hashtable.h
+++ b/deps/oblib/src/lib/hash/ob_hashtable.h
@@ -824,7 +824,6 @@ public:
       //memset(buckets_, 0, sizeof(hashbucket) * bucket_num);
       bucket_num_ = bucket_num;
       allocer_ = allocer;
-      allocer_->inc_ref();
       bucket_allocer_ = bucket_allocer;
     }
     return ret;
@@ -848,7 +847,6 @@ public:
           buckets_[i].node = NULL;
         }
       }
-      allocer_->dec_ref();
       allocer_ = NULL;
       //delete[] buckets_;
       //buckets_ = NULL;
diff --git a/deps/oblib/src/lib/hash/ob_hashutils.h b/deps/oblib/src/lib/hash/ob_hashutils.h
index 0833867c25..416e4e97cd 100644
--- a/deps/oblib/src/lib/hash/ob_hashutils.h
+++ b/deps/oblib/src/lib/hash/ob_hashutils.h
@@ -1225,8 +1225,9 @@ struct SimpleAllocerBlock
 
   int32_t ref_cnt;
   int32_t cur_pos;
-  char nodes_buffer[NODE_NUM *sizeof(Node)];
-  Node *nodes;
+  Node nodes[NODE_NUM];
+  Node *node_free_list;
+  Block *prev;
   Block *next;
 };
 
@@ -1239,7 +1240,7 @@ template <class T>
 struct NodeNumTraits<false, T>
 {
   static const int32_t NODE_NUM = (common::OB_MALLOC_NORMAL_BLOCK_SIZE -
-                                   24/*=sizeof(SimpleAllocerBlock 's members except nodes_buffer)*/ - 128/*for robust*/) /
+                                   24/*=sizeof(SimpleAllocerBlock 's members except nodes)*/ - 128/*for robust*/) /
                                   (32/*sizeof(SimpleAllocerNode's members except data)*/ + sizeof(T));
 };
 
@@ -1252,6 +1253,28 @@ struct NodeNumTraits<true, T>
 #define IS_BIG_OBJ(T) \
   ((common::OB_MALLOC_NORMAL_BLOCK_SIZE - 24 - 128) < (32 + sizeof(T)))
 
+/*
+block_free_list_:
+  Block C: node1->node2->node3...
+    ^
+    |
+  Block B: node1->node2->node3...
+    ^
+    |
+  Block A: node1->node2->node3...
+
+alloc:
+  1. fetch from block_free_list_
+  2. fetch from block_remainder_
+  3. alloc new block
+
+free:
+  check reference of block, zero-block will be destroy, block has 4 status:
+  1. in the block_free_list_
+  2. is the block_remainder_
+  3. in the block_remainder_ && is the block_remainder_
+  4. neither
+*/
 template <class T,
           int32_t NODE_NUM = NodeNumTraits<IS_BIG_OBJ(T), T>::NODE_NUM,
           class DefendMode = SpinMutexDefendMode,
@@ -1266,67 +1289,50 @@ class SimpleAllocer
   typedef typename DefendMode::lock_type lock_type;
   typedef typename DefendMode::lock_initer lock_initer;
 public:
-  SimpleAllocer() : block_list_head_(NULL), free_list_head_(NULL)
+  SimpleAllocer() : block_remainder_(NULL), block_free_list_(NULL)
   {
     lock_initer initer(lock_);
   }
   ~SimpleAllocer()
   {
-    clear();
+    OB_ASSERT(NULL == block_remainder_ &&
+              NULL == block_free_list_);
   }
   void set_attr(const ObMemAttr &attr) { allocer_.set_attr(attr); }
   void set_label(const lib::ObLabel &label) { allocer_.set_label(label); }
-  void clear()
-  {
-    Block *iter = block_list_head_;
-    while (NULL != iter) {
-      Block *next = iter->next;
-      if (0 != iter->ref_cnt) {
-        HASH_WRITE_LOG_RET(HASH_FATAL, OB_ERR_UNEXPECTED, "there is still node has not been free, ref_cnt=%d block=%p cur_pos=%d",
-                       iter->ref_cnt, iter, iter->cur_pos);
-      } else {
-        //delete iter;
-        allocer_.free(iter);
-      }
-      iter = next;
-    }
-    block_list_head_ = NULL;
-    free_list_head_ = NULL;
-  }
   template <class ... TYPES>
   T *alloc(TYPES&... args)
   {
     T *ret = NULL;
     mutexlocker locker(lock_);
-    if (NULL != free_list_head_) {
-      Node *node = free_list_head_;
+    if (NULL != block_free_list_) {
+      Block *block = block_free_list_;
+      Node *node = block->node_free_list;
       if (NODE_MAGIC1 != node->magic1 || NODE_MAGIC2 != node->magic2 || NULL == node->block) {
         HASH_WRITE_LOG_RET(HASH_FATAL, OB_ERR_UNEXPECTED, "magic broken magic1=%x magic2=%x", node->magic1, node->magic2);
       } else {
-        free_list_head_ = node->next;
+        block->node_free_list = node->next;
+        if (block->node_free_list == NULL) {
+          take_off_from_fl(block);
+        }
         node->block->ref_cnt++;
         ret = &(node->data);
       }
     } else {
-      Block *block = block_list_head_;
+      Block *block = block_remainder_;
       if (NULL == block || block->cur_pos >= (int32_t)NODE_NUM) {
-        //if (NULL == (block = new(std::nothrow) Block()))
         if (NULL == (block = (Block *)allocer_.alloc(sizeof(Block)))) {
           HASH_WRITE_LOG_RET(HASH_WARNING, OB_ERR_UNEXPECTED, "new block fail");
         } else {
-          // BACKTRACE(WARN, ((int64_t)sizeof(Block))>DEFAULT_BLOCK_SIZE,
-          // "hashutil alloc block=%ld node=%ld T=%ld N=%d",
-          //               sizeof(Block), sizeof(Node), sizeof(T), NODE_NUM);
-          //memset(block, 0, sizeof(Block));
           block->ref_cnt = 0;
           block->cur_pos = 0;
-          block->nodes = (Node *)(block->nodes_buffer);
-          block->next = block_list_head_;
-          block_list_head_ = block;
+          block->prev = block->next = NULL;
+          block->node_free_list = NULL;
+          block_remainder_ = block;
         }
       }
       if (NULL != block) {
-        Node *node = block->nodes + block->cur_pos;
+        Node *node = &block->nodes[block->cur_pos];
         block->cur_pos++;
         block->ref_cnt++;
         node->magic1 = NODE_MAGIC1;
@@ -1352,65 +1358,55 @@ public:
         HASH_WRITE_LOG_RET(HASH_FATAL, OB_ERR_UNEXPECTED, "magic broken magic1=%x magic2=%x", node->magic1, node->magic2);
       } else {
         data->~T();
-        node->block->ref_cnt--;
-        node->next = free_list_head_;
-        free_list_head_ = node;
+        Block *block = node->block;
+        block->ref_cnt--;
+        if (0 == block->ref_cnt) {
+          if (block == block_remainder_) {
+            block_remainder_ = NULL;
+          }
+          // non-NULL means this block is in the freelist
+          if (block->next != NULL) {
+            take_off_from_fl(block);
+          }
+          allocer_.free(block);
+        } else {
+          node->next = block->node_free_list;
+          block->node_free_list = node;
+          // NULL means this block isn't in the freelist
+          if (block->next == NULL) {
+            add_to_fl(block);
+          }
+        }
       }
     }
   }
-  void inc_ref()
+  void add_to_fl(Block *block)
   {
+    if (block_free_list_ == NULL) {
+      block->prev = block->next = block;
+      block_free_list_ = block;
+    } else {
+      block->prev = block_free_list_->prev;
+      block->next = block_free_list_;
+      block_free_list_->prev->next = block;
+      block_free_list_->prev = block;
+      block_free_list_ = block;
+    }
   }
-  void dec_ref()
+  void take_off_from_fl(Block *block)
   {
-  }
-  void gc()
-  {
-    mutexlocker locker(lock_);
-    if (NULL != free_list_head_ && NULL != block_list_head_) {
-      Block *block_iter = block_list_head_;
-      Block *block_next = NULL;
-      Block *block_prev = NULL;
-      while (NULL != block_iter) {
-        block_next = block_iter->next;
-        if (0 == block_iter->ref_cnt && 0 != block_iter->cur_pos) {
-          Node *node_iter = free_list_head_;
-          Node *node_prev = free_list_head_;
-          volatile int32_t counter = 0;
-          while (NULL != node_iter
-                 && counter < NODE_NUM) {
-            if (block_iter == node_iter->block) {
-              if (free_list_head_ == node_iter) {
-                free_list_head_ = node_iter->next;
-              } else {
-                node_prev->next = node_iter->next;
-              }
-              counter++;
-            } else {
-              node_prev = node_iter;
-            }
-            node_iter = node_iter->next;
-          }
-
-          if (block_list_head_ == block_iter) {
-            block_list_head_ = block_iter->next;
-          } else {
-            block_prev->next = block_iter->next;
-          }
-          //delete block_iter;
-          allocer_.free(block_iter);
-          HASH_WRITE_LOG(HASH_DEBUG, "free succ block=%p", block_iter);
-          block_iter = NULL;
-        } else {
-          block_prev = block_iter;
-        }
-        block_iter = block_next;
-      }
+    if (block == block->next) {
+      block_free_list_ = NULL;
+    } else {
+      block->prev->next = block->next;
+      block->next->prev = block->prev;
+      block_free_list_ = block->next;
+      block->prev = block->next = NULL;
     }
   }
 private:
-  Block *block_list_head_;
-  Node *free_list_head_;
+  Block *block_remainder_;
+  Block *block_free_list_;
   lock_type lock_;
   Allocer allocer_;
 };
diff --git a/deps/oblib/unittest/lib/hash/test_simpleallocer.cpp b/deps/oblib/unittest/lib/hash/test_simpleallocer.cpp
index a218710444..564b2c36cd 100644
--- a/deps/oblib/unittest/lib/hash/test_simpleallocer.cpp
+++ b/deps/oblib/unittest/lib/hash/test_simpleallocer.cpp
@@ -26,107 +26,41 @@ using namespace oceanbase;
 using namespace common;
 using namespace hash;
 
-const int64_t ITEM_NUM = 1024 * 128;
-
-struct data_t
+std::set<void *> ptr_set;
+class MyAllocator : public ObIAllocator
 {
-  uint32_t construct_flag;
-  char data[1024];
-  data_t()
+public:
+  void *alloc(const int64_t size)
   {
-    construct_flag = 0xffffffff;
-  };
-};
-
-typedef SimpleAllocer<data_t, 128> allocer_t;
-
-template <class T>
-void shuffle(T *array, const int64_t array_size)
-{
-  srand(static_cast<int32_t>(time(NULL)));
-  for (int64_t i = 0; i < array_size; i++)
-  {
-    int64_t swap_pos = rand() % array_size;
-    std::swap(array[i], array[swap_pos]);
+    void *ptr = ob_malloc(size);
+    ptr_set.insert(ptr);
+    return ptr;
   }
-}
+  void *alloc(const int64_t , const ObMemAttr &)
+    { return NULL; }
+  void free(void *ptr)
+  {
+    ptr_set.erase(ptr);
+  }
+};
 
 TEST(TestSimpleAllocer, allocate)
 {
-  allocer_t al;
-  data_t *nil = NULL;
-
-  data_t *store[ITEM_NUM];
-  for (int64_t i = 0; i < ITEM_NUM; i++)
-  {
-    EXPECT_NE(nil, (store[i] = al.alloc()));
-    EXPECT_EQ(0xffffffff, store[i]->construct_flag);
+  SimpleAllocer<int, 10, SpinMutexDefendMode, MyAllocator> alloc;
+  const int N = 100;
+  int *ptrs[N];
+  int i = N;
+  while (i--) {
+    int *ptr = alloc.alloc();
+    EXPECT_TRUE(ptr != NULL);
+    ptrs[i] = ptr;
   }
-  for (int64_t i = 0; i < ITEM_NUM; i++)
-  {
-    store[i]->construct_flag = 0x00000000;
-    al.free(store[i]);
+  i= N;
+  EXPECT_TRUE(!ptr_set.empty());
+  while (i--) {
+    alloc.free(ptrs[i]);
   }
-  for (int64_t i = ITEM_NUM - 1; i >= 0; i--)
-  {
-    data_t *tmp = NULL;
-    EXPECT_NE(nil, (tmp = al.alloc()));
-    EXPECT_EQ(0xffffffff, tmp->construct_flag);
-  }
-}
-
-TEST(TestSimpleAllocer, free)
-{
-  allocer_t al;
-
-  data_t *store[ITEM_NUM];
-  for (int64_t i = 0; i < ITEM_NUM; i++)
-  {
-    store[i] = al.alloc();
-  }
-  al.free(NULL);
-  shuffle(store, ITEM_NUM);
-  for (int64_t i = 0; i < ITEM_NUM; i++)
-  {
-    al.free(store[i]);
-  }
-  for (int64_t i = ITEM_NUM - 1; i >= 0; i--)
-  {
-    data_t *tmp = NULL;
-    EXPECT_EQ(store[i], (tmp = al.alloc()));
-  }
-  for (int64_t i = 0; i < ITEM_NUM; i++)
-  {
-    al.free(store[i]);
-    if (0 == i % 128)
-    {
-      al.gc();
-    }
-  }
-}
-
-TEST(TestSimpleAllocer, DISABLED_overflow)
-{
-  allocer_t al;
-  data_t *nil = NULL;
-  data_t *data[2];
-  data_t tmp;
-
-  EXPECT_NE(nil, (data[0] = al.alloc()));
-  // this case is used to test overflow
-  // copy more bytes than sizeof(data[0]). (actually safe)
-  // but Coverity treat it as a potential bug
-  memcpy(&tmp, data[0], sizeof(data_t) + sizeof(uint32_t));
-  memset(data[0], -1, sizeof(data_t) + sizeof(uint32_t));
-  al.free(data[0]);
-  memcpy(data[0], &tmp, sizeof(data_t) + sizeof(uint32_t));
-  al.free(data[0]);
-
-  memset(data[0], -1, sizeof(data_t) + sizeof(uint32_t));
-  EXPECT_EQ(nil, (data[1] = al.alloc()));
-  memcpy(data[0], &tmp, sizeof(data_t) + sizeof(uint32_t));
-  EXPECT_NE(nil, (data[1] = al.alloc()));
-  EXPECT_EQ(data[0], data[1]);
+  EXPECT_TRUE(ptr_set.empty());
 }
 
 int main(int argc, char **argv)