Allocate orig_list statically

tool_list is a temporary list needed only for SET SESSION session_track_system_variables, so allocate it on stack instead. Sane reinit() calls. Saves 2 new/delete per connection. Part of MDEV-14984 - regression in connect performance

Author: svoj

sql/session_tracker.cc

@@ -98,8 +98,7 @@ class Session_sysvars_tracker : public State_tracker
  my_hash_element(&m_registered_sysvars, i));
  }
  public:
- vars_list() :
- buffer_length(0)
+ vars_list(): buffer_length(0), track_all(false)
  {
  m_mem_flag= current_thd ? MY_THREAD_SPECIFIC : 0;
  init();
@@ -150,30 +149,16 @@ class Session_sysvars_tracker : public State_tracker
  Two objects of vars_list type are maintained to manage
  various operations.
  */
- vars_list *orig_list, *tool_list;
+ vars_list orig_list;
 
 public:
- Session_sysvars_tracker()
- {
- orig_list= new (std::nothrow) vars_list();
- tool_list= new (std::nothrow) vars_list();
- }
-
- ~Session_sysvars_tracker()
- {
- if (orig_list)
- delete orig_list;
- if (tool_list)
- delete tool_list;
- }
-
  size_t get_buffer_length()
  {
- return orig_list->get_buffer_length();
+ return orig_list.get_buffer_length();
  }
  bool construct_var_list(char *buf, size_t buf_len)
  {
- return orig_list->construct_var_list(buf, buf_len);
+ return orig_list.construct_var_list(buf, buf_len);
  }
 
  bool enable(THD *thd);
@@ -249,7 +234,6 @@ void Session_sysvars_tracker::vars_list::reinit()
 
 void Session_sysvars_tracker::vars_list::copy(vars_list* from, THD *thd)
 {
- reinit();
  track_all= from->track_all;
  free_hash();
  buffer_length= from->buffer_length;
@@ -271,10 +255,7 @@ bool Session_sysvars_tracker::vars_list::insert(const sys_var *svar)
  sysvar_node_st *node;
  if (!(node= (sysvar_node_st *) my_malloc(sizeof(sysvar_node_st),
  MYF(MY_WME | m_mem_flag))))
- {
- reinit();
  return true;
- }
 
  node->m_svar= (sys_var *)svar;
  node->test_load= node->m_svar->test_load;
@@ -285,7 +266,6 @@ bool Session_sysvars_tracker::vars_list::insert(const sys_var *svar)
  if (!search((sys_var *)svar))
  {
  //EOF (error is already reported)
- reinit();
  return true;
  }
  }
@@ -322,7 +302,6 @@ bool Session_sysvars_tracker::vars_list::parse_var_list(THD *thd,
  const char separator= ',';
  char *token, *lasts= NULL;
  size_t rest= var_list.length;
- reinit();
 
  if (!var_list.str || var_list.length == 0)
  {
@@ -573,14 +552,13 @@ bool Session_sysvars_tracker::enable(THD *thd)
  LEX_STRING tmp;
  tmp.str= global_system_variables.session_track_system_variables;
  tmp.length= safe_strlen(tmp.str);
- if (tool_list->parse_var_list(thd, tmp,
- true, thd->charset(), false) == true)
+ if (orig_list.parse_var_list(thd, tmp, true, thd->charset(), false) == true)
  {
  mysql_mutex_unlock(&LOCK_plugin);
+ orig_list.reinit();
  return true;
  }
  mysql_mutex_unlock(&LOCK_plugin);
- orig_list->copy(tool_list, thd);
  m_enabled= true;
 
  return false;
@@ -593,6 +571,9 @@ bool Session_sysvars_tracker::enable(THD *thd)
  Session_sysvars_tracker::vars_list::copy updating the hash in orig_list
  which represents the system variables to be tracked.
 
+ We are doing via tool list because there possible errors with memory
+ in this case value will be unchanged.
+
  @note This function is called from the ON_UPDATE() function of the
  session_track_system_variables' sys_var class.
 
@@ -604,15 +585,11 @@ bool Session_sysvars_tracker::enable(THD *thd)
 
 bool Session_sysvars_tracker::update(THD *thd, set_var *var)
 {
- /*
- We are doing via tool list because there possible errors with memory
- in this case value will be unchanged.
- */
- tool_list->reinit();
- if (tool_list->parse_var_list(thd, var->save_result.string_value, true,
- thd->charset(), true))
+ vars_list tool_list;
+ if (tool_list.parse_var_list(thd, var->save_result.string_value, true,
+ thd->charset(), true))
  return true;
- orig_list->copy(tool_list, thd);
+ orig_list.copy(&tool_list, thd);
  return false;
 }
 
@@ -694,13 +671,13 @@ bool Session_sysvars_tracker::vars_list::store(THD *thd, String *buf)
 
 bool Session_sysvars_tracker::store(THD *thd, String *buf)
 {
- if (!orig_list->is_enabled())
+ if (!orig_list.is_enabled())
  return false;
 
- if (orig_list->store(thd, buf))
+ if (orig_list.store(thd, buf))
  return true;
 
- orig_list->reset();
+ orig_list.reset();
 
  return false;
 }
@@ -721,7 +698,7 @@ void Session_sysvars_tracker::mark_as_changed(THD *thd,
  Check if the specified system variable is being tracked, if so
  mark it as changed and also set the class's m_changed flag.
  */
- if (orig_list->is_enabled() && (node= orig_list->insert_or_search(svar)))
+ if (orig_list.is_enabled() && (node= orig_list.insert_or_search(svar)))
  {
  node->m_changed= true;
  State_tracker::mark_as_changed(thd, var);