merge commit 02b00b154

Author: Marc Alff <marc.alff@oracle.com>
Date:   Thu Jul 30 11:17:50 2015 +0200

    Bug#21528683 SLOWDOWN CAUSED BY MEMSET IN SQL_DIGEST_STORAGE.RESET()

Author: vuvova

sql/sql_digest.h

@@ -41,6 +41,9 @@ struct sql_digest_storage
     For Example:
     SELECT * FROM T1;
     <SELECT_TOKEN> <*> <FROM_TOKEN> <ID_TOKEN> <2> <T1>
+
+    @note Only the first @c m_byte_count bytes are initialized,
+      out of @c m_token_array_length.
   */
   unsigned char *m_token_array;
   /* Length of the token array to be considered for DIGEST_TEXT calculation. */
@@ -63,10 +66,6 @@ struct sql_digest_storage
     m_full= false;
     m_byte_count= 0;
     m_charset_number= 0;
-    if (m_token_array_length > 0)
-    {
-      memset(m_token_array, 0, m_token_array_length);
-    }
     memset(m_md5, 0, MD5_HASH_SIZE);
   }