A system and status variables demo plugin

Let's see a more complex example. This plugin shows how to create system and status variables. It has one global system variable and one status variable, both defined as long long. When you set the global system variable, its value is copied into the status variable.

#include <stdio.h>
#include <mysql/plugin.h>
#include <mysql_version.h>
long long system_var = 0;
long long status_var = 0;
struct st_mysql_show_var vars_status_var[] =
{
{"vars_status_var", (char *) &status_var, SHOW_LONGLONG},
{0, 0, 0}
};

We have one status variable in this plugin called vars_status_var which is bound to the status_var variable defined near the top of this source code. We are defining this variable as long long so we use the SHOW_LONGLONG type.

int sysvar_check(MYSQL_THD thd,
struct st_mysql_sys_var *var,
void *save, struct st_mysql_value *value)
{

This function is to be called before our system variable is updated. A plugin is not required to...