Fetches the session/global/persist value of a system variable. More...

#include <mysql_system_variable.h>

Public Attributes
mysql_service_status_t(*	get )(THD hthd, const char variable_type, const char component_name, const char variable_name, void *val, size_t out_length_of_val)
	Gets the value of a system variable. More...

Detailed Description

Fetches the session/global/persist value of a system variable.

This is an example of using the service:

Call this to get the session/global/persist value of a variable. You can access both the component variables (SELECT ["@@"][scope "."]component_name "." variable_name; where scope ::= SESSION | LOCAL | GLOBAL) and the "legacy" system variables (SELECT ["@@"][scope "."].variable_name; where scope ::= SESSION | LOCAL | GLOBAL) that are registered by the server component. To access the latter you need to pass "mysql_server" (lowercase) as a component name.

A pointer to the value is returned into the val input/output argument. And the length of the value (as applicable) is returned into the out_length_of_val argument.

In case when the user buffer was too small to copy the value, the call fails and needed buffer size is returned by 'out_length_of_val'.

Decide on a variable storage type among one of "GLOBAL" or "SESSION"

Typical use (char * variable):

char *value, buffer_for_value[160];
size_t value_length;
const char *type = "GLOBAL";
 
value= &buffer_for_value[0];
value_length= sizeof(buffer_for_value) - 1;
mysql_service_mysql_system_variable_reader->get(nullptr, type, "foo", "bar",
         &value, &value_length);
printf("%.*s", (int) value_length, value);
 
To get the "SESSION" value the "hthd" should be passed :
MYSQL_THD hthd;
if (mysql_service_mysql_current_thread_reader->get(&hthd)) {
  my_error("%s\n", "mysql_current_thread_reader get() api failed");
}
mysql_service_mysql_system_variable_reader->get(
        hthd, "SESSION", "foo", "bar",
        &value, &value_length);

Member Data Documentation

◆ get

mysql_service_status_t(* s_mysql_mysql_system_variable_reader::get) (THD *hthd, const char *variable_type, const char *component_name, const char *variable_name, void **val, size_t *out_length_of_val)

Gets the value of a system variable.

Parameters

	hthd	thread session handle. if NULL, the GLOBAL value of the variable is returned.
	variable_type	one of [GLOBAL, SESSION].
	component_name	Name of the component or "mysql_server" for the legacy ones.
	variable_name	Name of the variable
[in,out]	val	On input: a buffer to hold the value. On output a pointer to the value.
[in,out]	out_length_of_val	On input: the buffer size. On output the length of the data copied.

Return values

true	failure
false	success

The documentation for this struct was generated from the following file:

include/mysql/components/services/mysql_system_variable.h

Public Attributes

Detailed Description

Member Data Documentation

◆ get