Remove THD::stmt_backup

sql/sql_class.cc:
  Statement constructor for the case when it's used for backup only
  was removed.
sql/sql_class.h:
  Remove THD::stmt_backup and simplify Statement constructors.
sql/sql_prepare.cc:
  Use an object on stack instead of THD::stmt_backup
sql/sql_select.cc:
  Use an object on stack instead of THD::stmt_backup

sql/sql_class.cc

@@ -156,9 +156,15 @@ bool foreign_key_prefix(Key *a, Key *b)
 /****************************************************************************
 ** Thread specific functions
 ****************************************************************************/
+/*
+  Pass nominal parameters to Statement constructor only to ensure that
+  the destructor works OK in case of error. The main_mem_root will be
+  re-initialized in init().
+*/
 
 THD::THD()
-  :user_time(0), global_read_lock(0), is_fatal_error(0),
+  :Statement(CONVENTIONAL_EXECUTION, 0, ALLOC_ROOT_MIN_BLOCK_SIZE, 0),
+   user_time(0), global_read_lock(0), is_fatal_error(0),
    rand_used(0), time_zone_used(0),
    last_insert_id_used(0), insert_id_used(0), clear_next_insert_id(0),
    in_lock_tables(0), bootstrap(0), derived_tables_processing(FALSE),
@@ -1483,9 +1489,10 @@ Query_arena::Type Query_arena::type() const
   Statement functions 
 */
 
-Statement::Statement(THD *thd)
-  :Query_arena(&main_mem_root, INITIALIZED),
-  id(++thd->statement_id_counter),
+Statement::Statement(enum enum_state state_arg, ulong id_arg,
+                     ulong alloc_block_size, ulong prealloc_size)
+  :Query_arena(&main_mem_root, state_arg),
+  id(id_arg),
   set_query_id(1),
   allow_sum_func(0),
   lex(&main_lex),
@@ -1494,33 +1501,7 @@ Statement::Statement(THD *thd)
   cursor(0)
 {
   name.str= NULL;
-  init_sql_alloc(&main_mem_root,
-                 thd->variables.query_alloc_block_size,
-                 thd->variables.query_prealloc_size);
-}
-
-/*
-  This constructor is called when Statement is a parent of THD and
-  for the backup statement. Some variables are initialized in
-  THD::init due to locking problems.
-*/
-
-Statement::Statement()
-  :Query_arena(&main_mem_root, CONVENTIONAL_EXECUTION),
-  id(0),
-  set_query_id(1),
-  allow_sum_func(0),                            /* initialized later */
-  lex(&main_lex),
-  query(0),                                     /* these two are set */ 
-  query_length(0),                              /* in alloc_query() */
-  cursor(0)
-{
-  /*
-    This is just to ensure that the destructor works correctly in
-    case of an error and the backup statement. The memory root will
-    be re-initialized in THD::init.
-  */
-  init_sql_alloc(&main_mem_root, ALLOC_ROOT_MIN_BLOCK_SIZE, 0);
+  init_sql_alloc(&main_mem_root, alloc_block_size, prealloc_size);
 }
 
 

sql/sql_class.h

@@ -809,13 +809,11 @@ public:
 
 public:
 
-  /*
-    This constructor is called when statement is a subobject of THD:
-    some variables are initialized in THD::init due to locking problems
-  */
-  Statement();
+  /* This constructor is called for backup statements */
+  Statement() { clear_alloc_root(&main_mem_root); }
 
-  Statement(THD *thd);
+  Statement(enum enum_state state_arg, ulong id_arg,
+            ulong alloc_block_size, ulong prealloc_size);
   virtual ~Statement();
 
   /* Assign execution context (note: not all members) of given stmt to self */
@@ -957,11 +955,6 @@ public:
   pthread_mutex_t LOCK_delete;		// Locked before thd is deleted
   /* all prepared statements and cursors of this connection */
   Statement_map stmt_map; 
-  /*
-    keeps THD state while it is used for active statement
-    Note: we perform special cleanup for it in THD destructor.
-  */
-  Statement stmt_backup;
   /*
     A pointer to the stack frame of handle_one_connection(),
     which is called first in the thread for handling a client

sql/sql_prepare.cc

@@ -1706,6 +1706,7 @@ bool mysql_stmt_prepare(THD *thd, char *packet, uint packet_length,
                         LEX_STRING *name)
 {
   LEX *lex;
+  Statement stmt_backup;
   Prepared_statement *stmt= new Prepared_statement(thd);
   bool error;
   DBUG_ENTER("mysql_stmt_prepare");
@@ -1739,13 +1740,13 @@ bool mysql_stmt_prepare(THD *thd, char *packet, uint packet_length,
     DBUG_RETURN(TRUE);
   }
 
-  thd->set_n_backup_statement(stmt, &thd->stmt_backup);
-  thd->set_n_backup_item_arena(stmt, &thd->stmt_backup);
+  thd->set_n_backup_statement(stmt, &stmt_backup);
+  thd->set_n_backup_item_arena(stmt, &stmt_backup);
 
   if (alloc_query(thd, packet, packet_length))
   {
-    thd->restore_backup_statement(stmt, &thd->stmt_backup);
-    thd->restore_backup_item_arena(stmt, &thd->stmt_backup);
+    thd->restore_backup_statement(stmt, &stmt_backup);
+    thd->restore_backup_item_arena(stmt, &stmt_backup);
     /* Statement map deletes statement on erase */
     thd->stmt_map.erase(stmt);
     DBUG_RETURN(TRUE);
@@ -1770,7 +1771,7 @@ bool mysql_stmt_prepare(THD *thd, char *packet, uint packet_length,
     transformation can be reused on execute, we set again thd->mem_root from
     stmt->mem_root (see setup_wild for one place where we do that).
   */
-  thd->restore_backup_item_arena(stmt, &thd->stmt_backup);
+  thd->restore_backup_item_arena(stmt, &stmt_backup);
 
   if (!error)
     error= check_prepared_statement(stmt, test(name));
@@ -1786,7 +1787,7 @@ bool mysql_stmt_prepare(THD *thd, char *packet, uint packet_length,
   lex_end(lex);
   close_thread_tables(thd);
   cleanup_stmt_and_thd_after_use(stmt, thd);
-  thd->restore_backup_statement(stmt, &thd->stmt_backup);
+  thd->restore_backup_statement(stmt, &stmt_backup);
   thd->current_arena= thd;
 
   if (error)
@@ -1949,6 +1950,7 @@ void mysql_stmt_execute(THD *thd, char *packet, uint packet_length)
 {
   ulong stmt_id= uint4korr(packet);
   ulong flags= (ulong) ((uchar) packet[4]);
+  Statement stmt_backup;
   Cursor *cursor;
   /*
     Query text for binary log, or empty string if the query is not put into
@@ -2026,8 +2028,7 @@ void mysql_stmt_execute(THD *thd, char *packet, uint packet_length)
   if (stmt->param_count && stmt->set_params_data(stmt, &expanded_query))
     goto set_params_data_err;
 #endif
-  thd->stmt_backup.set_statement(thd);
-  thd->set_statement(stmt);
+  thd->set_n_backup_statement(stmt, &stmt_backup);
   thd->current_arena= stmt;
   reinit_stmt_before_use(thd, stmt->lex);
   /* From now cursors assume that thd->mem_root is clean */
@@ -2064,7 +2065,7 @@ void mysql_stmt_execute(THD *thd, char *packet, uint packet_length)
     reset_stmt_params(stmt);
   }
 
-  thd->set_statement(&thd->stmt_backup);
+  thd->set_statement(&stmt_backup);
   thd->current_arena= thd;
   DBUG_VOID_RETURN;
 
@@ -2089,6 +2090,7 @@ void mysql_sql_stmt_execute(THD *thd, LEX_STRING *stmt_name)
     binary log.
   */
   String expanded_query;
+  Statement stmt_backup;
   DBUG_ENTER("mysql_sql_stmt_execute");
 
   DBUG_ASSERT(thd->free_list == NULL);
@@ -2110,16 +2112,16 @@ void mysql_sql_stmt_execute(THD *thd, LEX_STRING *stmt_name)
 
   /* Must go before setting variables, as it clears thd->user_var_events */
   mysql_reset_thd_for_next_command(thd);
-  thd->set_n_backup_statement(stmt, &thd->stmt_backup);
-  thd->set_statement(stmt);
+  thd->set_n_backup_statement(stmt, &stmt_backup);
   if (stmt->set_params_from_vars(stmt,
-                                 thd->stmt_backup.lex->prepared_stmt_params,
+                                 stmt_backup.lex->prepared_stmt_params,
                                  &expanded_query))
   {
     my_error(ER_WRONG_ARGUMENTS, MYF(0), "EXECUTE");
   }
   thd->command= COM_STMT_EXECUTE; /* For nice messages in general log */
   execute_stmt(thd, stmt, &expanded_query);
+  thd->set_statement(&stmt_backup);
   DBUG_VOID_RETURN;
 }
 
@@ -2176,7 +2178,6 @@ static void execute_stmt(THD *thd, Prepared_statement *stmt,
   close_thread_tables(thd);                    // to close derived tables
   cleanup_stmt_and_thd_after_use(stmt, thd);
   reset_stmt_params(stmt);
-  thd->set_statement(&thd->stmt_backup);
   thd->current_arena= thd;
 
   if (stmt->state == Query_arena::PREPARED)
@@ -2201,6 +2202,7 @@ void mysql_stmt_fetch(THD *thd, char *packet, uint packet_length)
   ulong stmt_id= uint4korr(packet);
   ulong num_rows= uint4korr(packet+4);
   Prepared_statement *stmt;
+  Statement stmt_backup;
   DBUG_ENTER("mysql_stmt_fetch");
 
   statistic_increment(thd->status_var.com_stmt_fetch, &LOCK_status);
@@ -2214,7 +2216,7 @@ void mysql_stmt_fetch(THD *thd, char *packet, uint packet_length)
   }
 
   thd->current_arena= stmt;
-  thd->set_n_backup_statement(stmt, &thd->stmt_backup);
+  thd->set_n_backup_statement(stmt, &stmt_backup);
 
   if (!(specialflag & SPECIAL_NO_PRIOR))
     my_pthread_setprio(pthread_self(), QUERY_PRIOR);
@@ -2226,7 +2228,7 @@ void mysql_stmt_fetch(THD *thd, char *packet, uint packet_length)
   if (!(specialflag & SPECIAL_NO_PRIOR))
     my_pthread_setprio(pthread_self(), WAIT_PRIOR);
 
-  thd->restore_backup_statement(stmt, &thd->stmt_backup);
+  thd->restore_backup_statement(stmt, &stmt_backup);
   thd->current_arena= thd;
 
   if (!stmt->cursor->is_open())
@@ -2386,7 +2388,9 @@ void mysql_stmt_get_longdata(THD *thd, char *packet, ulong packet_length)
 
 
 Prepared_statement::Prepared_statement(THD *thd_arg)
-  :Statement(thd_arg),
+  :Statement(INITIALIZED, ++thd_arg->statement_id_counter,
+             thd_arg->variables.query_alloc_block_size,
+             thd_arg->variables.query_prealloc_size),
   thd(thd_arg),
   param_array(0),
   param_count(0),

sql/sql_select.cc

@@ -1824,6 +1824,7 @@ Cursor::fetch(ulong num_rows)
   THD *thd= join->thd;
   JOIN_TAB *join_tab= join->join_tab + join->const_tables;
   enum_nested_loop_state error= NESTED_LOOP_OK;
+  Query_arena backup_arena;
   DBUG_ENTER("Cursor::fetch");
   DBUG_PRINT("enter",("rows: %lu", num_rows));
 
@@ -1835,7 +1836,7 @@ Cursor::fetch(ulong num_rows)
   thd->lock= lock;
   thd->query_id= query_id;
   /* save references to memory, allocated during fetch */
-  thd->set_n_backup_item_arena(this, &thd->stmt_backup);
+  thd->set_n_backup_item_arena(this, &backup_arena);
 
   join->fetch_limit+= num_rows;
 
@@ -1851,7 +1852,7 @@ Cursor::fetch(ulong num_rows)
     ha_release_temporary_latches(thd);
 #endif
 
-  thd->restore_backup_item_arena(this, &thd->stmt_backup);
+  thd->restore_backup_item_arena(this, &backup_arena);
   DBUG_ASSERT(thd->free_list == 0);
   reset_thd(thd);