Fix for bug #17260 "Multiple invocations of triggers or stored functions

hog memory".

During each invocation of stored function or trigger some objects which
lifetime is one function call (e.g. sp_rcontext) were allocated on
arena/memroot of calling statement. This led to consumption of fixed amount
of memory for each function/trigger invocation and so statements which
involve lot of them were hogging memory. This in its return led to OOM
crashes or freezes.

This fix introduces new memroot and arena for objects which lifetime is
whole duration of function call. So all memory consumed by such objects
is freed at the end of function call.


sql/sp_head.cc:
  sp_head::execute_function():
    Introduced new memroot and arena for objects which lifetime is whole
    duration of function call (e.g. sp_rcontext, sp_cursor). We can't
    use caller's arena/memroot for those objects because in this case 
    some fixed amount of memory will be consumed for each function/trigger
    invocation and so statements which involve lot of them will hog memory.
    Got rid of param_values array to avoid excessive juggling with arenas.

sql/sp_head.cc

@@ -1209,130 +1209,144 @@ bool
 sp_head::execute_function(THD *thd, Item **argp, uint argcount,
                           Field *return_value_fld)
 {
-  Item_cache **param_values;
   ulonglong binlog_save_options;
   bool need_binlog_call;
-  uint params;
+  uint arg_no;
   sp_rcontext *octx = thd->spcont;
   sp_rcontext *nctx = NULL;
+  char buf[STRING_BUFFER_USUAL_SIZE];
+  String binlog_buf(buf, sizeof(buf), &my_charset_bin);
   bool err_status= FALSE;
+  MEM_ROOT call_mem_root;
+  Query_arena call_arena(&call_mem_root, Query_arena::INITIALIZED_FOR_SP);
+  Query_arena backup_arena;
 
   DBUG_ENTER("sp_head::execute_function");
   DBUG_PRINT("info", ("function %s", m_name.str));
 
-  params = m_pcont->context_var_count();
-
   /*
     Check that the function is called with all specified arguments.
 
     If it is not, use my_error() to report an error, or it will not terminate
     the invoking query properly.
   */
-
-  if (argcount != params)
+  if (argcount != m_pcont->context_var_count())
   {
     /*
       Need to use my_error here, or it will not terminate the
       invoking query properly.
     */
     my_error(ER_SP_WRONG_NO_OF_ARGS, MYF(0),
-             "FUNCTION", m_qname.str, params, argcount);
+             "FUNCTION", m_qname.str, m_pcont->context_var_count(), argcount);
     DBUG_RETURN(TRUE);
   }
-
-  /* Allocate param_values to be used for dumping the call into binlog. */
-
-  if (!(param_values= (Item_cache**)thd->alloc(sizeof(Item_cache*)*argcount)))
-    DBUG_RETURN(TRUE);
-
-  // QQ Should have some error checking here? (types, etc...)
+  /*
+    Prepare arena and memroot for objects which lifetime is whole
+    duration of function call (sp_rcontext, it's tables and items,
+    sp_cursor and Item_cache holders for case expressions).
+    We can't use caller's arena/memroot for those objects because
+    in this case some fixed amount of memory will be consumed for
+    each function/trigger invocation and so statements which involve
+    lot of them will hog memory.
+    TODO: we should create sp_rcontext once per command and reuse
+    it on subsequent executions of a function/trigger.
+  */
+  init_sql_alloc(&call_mem_root, MEM_ROOT_BLOCK_SIZE, 0);
+  thd->set_n_backup_active_arena(&call_arena, &backup_arena);
 
   if (!(nctx= new sp_rcontext(m_pcont, return_value_fld, octx)) ||
       nctx->init(thd))
   {
-    delete nctx; /* Delete nctx if it was init() that failed. */
-    DBUG_RETURN(TRUE);
+    thd->restore_active_arena(&call_arena, &backup_arena);
+    err_status= TRUE;
+    goto err_with_cleanup;
   }
 
+  /*
+    We have to switch temporarily back to callers arena/memroot.
+    Function arguments belong to the caller and so the may reference
+    memory which they will allocate during calculation long after
+    this function call will be finished (e.g. in Item::cleanup()).
+  */
+  thd->restore_active_arena(&call_arena, &backup_arena);
+
 #ifndef DBUG_OFF
   nctx->sp= this;
 #endif
 
   /* Pass arguments. */
+  for (arg_no= 0; arg_no < argcount; arg_no++)
+  {
+    /* Arguments must be fixed in Item_func_sp::fix_fields */
+    DBUG_ASSERT(argp[arg_no]->fixed);
 
+    if ((err_status= nctx->set_variable(thd, arg_no, argp[arg_no])))
+      goto err_with_cleanup;
+  }
+
+  need_binlog_call= mysql_bin_log.is_open() && (thd->options & OPTION_BIN_LOG);
+
+  /*
+    Remember the original arguments for unrolled replication of functions
+    before they are changed by execution.
+  */
+  if (need_binlog_call)
   {
-    uint i;
-    
-    for (i= 0 ; i < argcount ; i++)
+    binlog_buf.length(0);
+    binlog_buf.append(STRING_WITH_LEN("SELECT "));
+    append_identifier(thd, &binlog_buf, m_name.str, m_name.length);
+    binlog_buf.append('(');
+    for (arg_no= 0; arg_no < argcount; arg_no++)
     {
-      if (!argp[i]->fixed && argp[i]->fix_fields(thd, &argp[i]))
-      {
-        err_status= TRUE;
-        break;
-      }
+      String str_value_holder;
+      String *str_value;
 
-      param_values[i]= Item_cache::get_cache(argp[i]->result_type());
-      param_values[i]->store(argp[i]);
+      if (arg_no)
+        binlog_buf.append(',');
 
-      if (nctx->set_variable(thd, i, param_values[i]))
-      {
-        err_status= TRUE;
-        break;
-      }
-    }
-  }
+      str_value= sp_get_item_value(nctx->get_item(arg_no),
+                                   &str_value_holder);
 
-  if (err_status)
-  {
-    delete nctx;
-    DBUG_RETURN(TRUE);
+      if (str_value)
+        binlog_buf.append(*str_value);
+      else
+        binlog_buf.append(STRING_WITH_LEN("NULL"));
+    }
+    binlog_buf.append(')');
   }
-
   thd->spcont= nctx;
 
   binlog_save_options= thd->options;
-  need_binlog_call= mysql_bin_log.is_open() && (thd->options & OPTION_BIN_LOG);
   if (need_binlog_call)
   {
     reset_dynamic(&thd->user_var_events);
     mysql_bin_log.start_union_events(thd);
   }
-    
+
+  /*
+    Switch to call arena/mem_root so objects like sp_cursor or
+    Item_cache holders for case expressions can be allocated on it.
+
+    TODO: In future we should associate call arena/mem_root with
+          sp_rcontext and allocate all these objects (and sp_rcontext
+          itself) on it directly rather than juggle with arenas.
+  */
+  thd->set_n_backup_active_arena(&call_arena, &backup_arena);
+
   thd->options&= ~OPTION_BIN_LOG;
   err_status= execute(thd);
   thd->options= binlog_save_options;
-  
+
+  thd->restore_active_arena(&call_arena, &backup_arena);
+
   if (need_binlog_call)
     mysql_bin_log.stop_union_events(thd);
 
   if (need_binlog_call && thd->binlog_evt_union.unioned_events)
   {
-    char buf[256];
-    String bufstr(buf, sizeof(buf), &my_charset_bin);
-    bufstr.length(0);
-    bufstr.append(STRING_WITH_LEN("SELECT "));
-    append_identifier(thd, &bufstr, m_name.str, m_name.length);
-    bufstr.append('(');
-    for (uint i=0; i < argcount; i++)
-    {
-      String str_value_holder;
-      String *str_value;
-
-      if (i)
-        bufstr.append(',');
-
-      str_value= sp_get_item_value(param_values[i], &str_value_holder);
-
-      if (str_value)
-        bufstr.append(*str_value);
-      else
-        bufstr.append(STRING_WITH_LEN("NULL"));
-    }
-    bufstr.append(')');
-    
-    Query_log_event qinfo(thd, bufstr.ptr(), bufstr.length(),
+    Query_log_event qinfo(thd, binlog_buf.ptr(), binlog_buf.length(),
                           thd->binlog_evt_union.unioned_events_trans, FALSE);
-    if (mysql_bin_log.write(&qinfo) && 
+    if (mysql_bin_log.write(&qinfo) &&
         thd->binlog_evt_union.unioned_events_trans)
     {
       push_warning(thd, MYSQL_ERROR::WARN_LEVEL_WARN, ER_UNKNOWN_ERROR,
@@ -1353,8 +1367,13 @@ sp_head::execute_function(THD *thd, Item **argp, uint argcount,
     }
   }
 
+
   nctx->pop_all_cursors();	// To avoid memory leaks after an error
+
+err_with_cleanup:
   delete nctx;
+  call_arena.free_items();
+  free_root(&call_mem_root, MYF(0));
   thd->spcont= octx;
 
   DBUG_RETURN(err_status);