diff --git a/dbms/src/Common/Arena.h b/dbms/src/Common/Arena.h
index f354ac773dc..7415cde5fbf 100644
--- a/dbms/src/Common/Arena.h
+++ b/dbms/src/Common/Arena.h
@@ -53,9 +53,7 @@ class Arena : private boost::noncopyable
         ~Chunk()
         {
             Allocator::free(begin, size());
-
-            if (prev)
-                delete prev;
+            delete prev;
         }
 
         size_t size() const { return end - begin; }
@@ -101,7 +99,7 @@ class Arena : private boost::noncopyable
     friend class ArenaAllocator;
 
 public:
-    Arena(size_t initial_size_ = 4096, size_t growth_factor_ = 2, size_t linear_growth_threshold_ = 128 * 1024 * 1024)
+    explicit Arena(size_t initial_size_ = 4096, size_t growth_factor_ = 2, size_t linear_growth_threshold_ = 128 * 1024 * 1024)
         : growth_factor(growth_factor_)
         , linear_growth_threshold(linear_growth_threshold_)
         , head(new Chunk(initial_size_, nullptr))
@@ -122,7 +120,7 @@ class Arena : private boost::noncopyable
             void * head_pos = head->pos;
             size_t space = head->end - head->pos;
 
-            auto res = static_cast<char *>(std::align(alignment, size, head_pos, space));
+            auto * res = static_cast<char *>(std::align(alignment, size, head_pos, space));
             if (res)
             {
                 head->pos = static_cast<char *>(head_pos);
diff --git a/dbms/src/Common/ArenaWithFreeLists.h b/dbms/src/Common/ArenaWithFreeLists.h
index bc96951dd4e..0d269472ad6 100644
--- a/dbms/src/Common/ArenaWithFreeLists.h
+++ b/dbms/src/Common/ArenaWithFreeLists.h
@@ -44,7 +44,7 @@ class ArenaWithFreeLists : private Allocator<false>
     Block * free_lists[16]{};
 
 public:
-    ArenaWithFreeLists(
+    explicit ArenaWithFreeLists(
         const size_t initial_size = 4096,
         const size_t growth_factor = 2,
         const size_t linear_growth_threshold = 128 * 1024 * 1024)
@@ -64,7 +64,7 @@ class ArenaWithFreeLists : private Allocator<false>
         if (auto & free_block_ptr = free_lists[list_idx])
         {
             /// Let's take it. And change the head of the list to the next item in the list.
-            const auto res = free_block_ptr->data;
+            auto * const res = free_block_ptr->data;
             free_block_ptr = free_block_ptr->next;
             return res;
         }
@@ -83,7 +83,7 @@ class ArenaWithFreeLists : private Allocator<false>
 
         /// Insert the released block into the head of the list.
         auto & free_block_ptr = free_lists[list_idx];
-        const auto old_head = free_block_ptr;
+        auto * const old_head = free_block_ptr;
         free_block_ptr = reinterpret_cast<Block *>(ptr);
         free_block_ptr->next = old_head;
     }
diff --git a/dbms/src/Common/ArrayCache.h b/dbms/src/Common/ArrayCache.h
index fd716d1ab95..8110a27c580 100644
--- a/dbms/src/Common/ArrayCache.h
+++ b/dbms/src/Common/ArrayCache.h
@@ -269,7 +269,7 @@ class ArrayCache : private boost::noncopyable
     /// Represents pending insertion attempt.
     struct InsertToken
     {
-        InsertToken(ArrayCache & cache_)
+        explicit InsertToken(ArrayCache & cache_)
             : cache(cache_)
         {}
 
@@ -546,7 +546,7 @@ class ArrayCache : private boost::noncopyable
 
 
 public:
-    ArrayCache(size_t max_total_size_)
+    explicit ArrayCache(size_t max_total_size_)
         : max_total_size(max_total_size_)
     {
     }
diff --git a/dbms/src/Common/AutoArray.h b/dbms/src/Common/AutoArray.h
index d7629b9d1dd..eebff46dd7f 100644
--- a/dbms/src/Common/AutoArray.h
+++ b/dbms/src/Common/AutoArray.h
@@ -99,7 +99,7 @@ class AutoArray
 
     size_t size() const
     {
-        return m_size();
+        return mSize();
     }
 
     bool empty() const
@@ -208,12 +208,12 @@ class AutoArray
 private:
     char * data;
 
-    size_t & m_size()
+    size_t & mSize()
     {
         return reinterpret_cast<size_t *>(data)[-1];
     }
 
-    size_t m_size() const
+    size_t mSize() const
     {
         return reinterpret_cast<const size_t *>(data)[-1];
     }
@@ -243,7 +243,7 @@ class AutoArray
 
         data = new char[size_ * sizeof(T) + sizeof(size_t)];
         data += sizeof(size_t);
-        m_size() = size_;
+        mSize() = size_;
 
         if (!dont_init_elems)
             for (size_t i = 0; i < size_; ++i)