Document stats_mysql_global.max_connect_timeouts

[cswingler]

The statistic for max_connect_timeouts in the stats_mysql_global table is marked as "ToDo"

After reviewing the code, this documentation should read:

Number of times that a MySQL connection has exceed the mysql-connect_timeout_server_max global variable.

[cswingler]

Supporting notes:

mysql-connect_timeout_server_max is mapped to max_connect_time:

proxysql/lib/MySQL_Session.cpp

Lines 3403 to 3407 in 065ee92

	if (mysql_thread___connect_timeout_server_max) {
	if (mybe->server_myds->max_connect_time==0) {
	mybe->server_myds->max_connect_time=thread->curtime+mysql_thread___connect_timeout_server_max*1000;
	}
	}

And st_var_max_connect_timeout_err maps to p_th_counter::max_connect_timeouts:

proxysql/lib/MySQL_Thread.cpp

Line 161 in 065ee92

{ st_var_max_connect_timeout_err, p_th_counter::max_connect_timeouts, (char *)"max_connect_timeouts" },

Which is iterated if a timeout is exceeded:

proxysql/lib/MySQL_Session.cpp

Lines 3205 to 3220 in 065ee92

	if (thread->curtime >= mybe->server_myds->max_connect_time) {
	if (mirror) {
	PROXY_TRACE();
	}
	string errmsg {};
	const string session_info { session_fast_forward ? "for 'fast_forward' session " : "" };
	const uint64_t query_time = (thread->curtime - CurrentQuery.start_time)/1000;
	string_format(
	"Max connect timeout reached while reaching hostgroup %d %safter %llums",
	errmsg, current_hostgroup, session_info.c_str(), query_time
	);
	if (thread) {
	thread->status_variables.stvar[st_var_max_connect_timeout_err]++;

so that gets iterated if we exceed mysql-connect_timeout_server_max.

https://proxysql.com/documentation/global-variables/mysql-variables/#mysql-connect_timeout_server_max