option to free_root() to not my_free() the blocks

fixed bug/updated count_distinct2 test
changed reset in count distinct to avoid calls to my_free()


include/my_sys.h:
  option to free_root() not to do my_free()
include/my_tree.h:
  reset_tree()
mysql-test/r/count_distinct2.result:
  added group by test
mysql-test/t/count_distinct2.test:
  group by test + fixed bug - need to drop table
mysys/my_alloc.c:
  mark_blocks_free()
mysys/tree.c:
  reset_tree()
sql/item_sum.cc:
  in count distinct reset_tree instead of delete_tree

1 files changed, 40 insertions, 1 deletions

diff --git a/mysys/my_alloc.c b/mysys/my_alloc.c
index db482454e69..b82ff965dfb 100644
--- a/mysys/my_alloc.c
+++ b/mysys/my_alloc.c
@@ -100,7 +100,41 @@ gptr alloc_root(MEM_ROOT *mem_root,unsigned int Size)
 #endif
 }
 
-	/* deallocate everything used by alloc_root */
+static inline void mark_blocks_free(MEM_ROOT* root)
+{
+  reg1 USED_MEM *next,*last = 0;
+
+  /* iterate through (partially) free blocks, mark them fully free */
+  for(next = root->free; next; next = next->next )
+    {
+      last = next;
+      next->left = next->size - ALIGN_SIZE(sizeof(USED_MEM));
+    }
+  /* if free block list was not empty, point the next of the
+     last free block to the beginning of the used list  */
+  next = root->used; /* a little optimization to avoid dereferencing root
+		      twice - we will shortly start iterating through used
+		      list */
+  if(last)
+    last->next = next;
+  else /* if free list is empty, just point it to the current used*/
+    root->free = next;
+
+  /* now go through the current used list, and mark each block
+     as fully free. Note that because of our optimization, we do not
+     need to initialize next here - see above
+  */
+  for(;next; next = next->next)
+      next->left = next->size - ALIGN_SIZE(sizeof(USED_MEM));
+
+  /* Now everything is set - we just need to indicate that nothing is used
+     anymore
+  */
+  root->used = 0;
+}
+
+	/* deallocate everything used by alloc_root or just move
+	 used blocks to free list if called with MY_USED_TO_FREE */
 
 void free_root(MEM_ROOT *root, myf MyFlags)
 {
@@ -109,6 +143,11 @@ void free_root(MEM_ROOT *root, myf MyFlags)
 
   if (!root)
     DBUG_VOID_RETURN; /* purecov: inspected */
+  if(MyFlags & MY_MARK_BLOCKS_FREE)
+    {
+      mark_blocks_free(root);
+      DBUG_VOID_RETURN;
+    }
   if (!(MyFlags & MY_KEEP_PREALLOC))
     root->pre_alloc=0;