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MDEV-32013 Add Field::val_lex_string_strmake()

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There are two functions to extract a Field::val_str() value
as a LEX_STRING or LEX_CSTRING pointing to the data allocated on a MEM_ROOT:

  char *get_field(MEM_ROOT *mem, Field *field);
  bool get_field(MEM_ROOT *mem, Field *field, class String *res);

The first function requires strlen() calls to make a LEX_CSTRING/LEX_STRING.
The second function requires a redundant String buffer,
which is used only as a temporary proxy value pointing to a MEM_ROOT fragment
(and does not use any String dynamic allocation methods).

This patch add a native way to extract a Field::val_str() value
as a LEX_STRING or LEX_CSTRING pointing to a MEM_ROOT fragment.
It helps to remove redundant strlen() calls and redundant String buffers.

- Adding a new method:

    LEX_STRING Field::val_lex_string_strmake(MEM_ROOT *mem);

- Reusing the new method Field::val_lex_string_strmake() in;

    bool get_field(MEM_ROOT *mem, Field *field, String *res);

  Also, moving it from table.cc to a static function in sql_help.cc.
  It is used in sql_help.cc only, and we don't want it to be reused
  in other parts of the code (to avoid redundant String buffers).

- Reusing the new method Field::val_lex_string_strmake() in this function:

    char *get_field(MEM_ROOT *mem, Field *field);

- Replacing get_field() to Field::val_lex_string_strmake() in these files:

    sql_plugin.cc  (redundant String buffers were removed)
    sql_udf.cc     (redundant strlen() calls were removed)

Note, this function:

   char *get_field(MEM_ROOT *mem, Field *field);

is still used in a number of files:

   event_data_objects.cc
   event_db_repository.cc
   sql_acl.cc
   sql_servers.cc

These remaining calls will be removed by separate patches,
and get_field() will be removed after that.
This commit is contained in:
Alexander Barkov
2023-08-25 16:06:34 +04:00
parent 781ec16bd9
commit e0949cd6f0
7 changed files with 65 additions and 51 deletions
Download Patch File Download Diff File Expand all files Collapse all files

11
sql/sql_plugin.cc
View File

@ -1883,12 +1883,11 @@ static void plugin_load(MEM_ROOT *tmp_root)
while (!(error= read_record_info.read_record()))
{
DBUG_PRINT("info", ("init plugin record"));
String str_name, str_dl;
get_field(tmp_root, table->field[0], &str_name);
get_field(tmp_root, table->field[1], &str_dl);
LEX_CSTRING name= {str_name.ptr(), str_name.length()};
LEX_CSTRING dl= {str_dl.ptr(), str_dl.length()};
DBUG_ASSERT(new_thd == table->field[0]->get_thd());
DBUG_ASSERT(new_thd == table->field[1]->get_thd());
DBUG_ASSERT(!(new_thd->variables.sql_mode & MODE_PAD_CHAR_TO_FULL_LENGTH));
LEX_CSTRING name= table->field[0]->val_lex_string_strmake(tmp_root);
LEX_CSTRING dl= table->field[1]->val_lex_string_strmake(tmp_root);
if (!name.length || !dl.length)
continue;