Add variable client_multi_statements to address #1074

See comments in Github issue. Once applied, this change
allows the user to toggle the 'client_multi_statements'
flag as a global variable.

include/MySQL_Thread.h

@@ -347,6 +347,7 @@ class MySQL_Threads_Handler
 		int shun_on_failures;
 		int shun_recovery_time_sec;
 		int query_retries_on_failure;
+		bool client_multi_statements;
 		int connect_retries_on_failure;
 		int connect_retries_delay;
 		int connection_delay_multiplex_ms;

include/proxysql_structs.h

@@ -614,6 +614,7 @@ __thread int mysql_thread___ping_timeout_server;
 __thread int mysql_thread___shun_on_failures;
 __thread int mysql_thread___shun_recovery_time_sec;
 __thread int mysql_thread___query_retries_on_failure;
+__thread bool mysql_thread___client_multi_statements;
 __thread int mysql_thread___connect_retries_on_failure;
 __thread int mysql_thread___connect_retries_delay;
 __thread int mysql_thread___connection_delay_multiplex_ms;
@@ -724,6 +725,7 @@ extern __thread int mysql_thread___ping_timeout_server;
 extern __thread int mysql_thread___shun_on_failures;
 extern __thread int mysql_thread___shun_recovery_time_sec;
 extern __thread int mysql_thread___query_retries_on_failure;
+extern __thread bool mysql_thread___client_multi_statements;
 extern __thread int mysql_thread___connect_retries_on_failure;
 extern __thread int mysql_thread___connect_retries_delay;
 extern __thread int mysql_thread___connection_delay_multiplex_ms;

lib/MySQL_Thread.cpp

@@ -211,6 +211,7 @@ static char * mysql_thread_variables_names[]= {
 	(char *)"shun_on_failures",
 	(char *)"shun_recovery_time_sec",
 	(char *)"query_retries_on_failure",
+	(char *)"client_multi_statements",
 	(char *)"connect_retries_on_failure",
 	(char *)"connect_retries_delay",
 	(char *)"connection_delay_multiplex_ms",
@@ -342,6 +343,7 @@ MySQL_Threads_Handler::MySQL_Threads_Handler() {
 	variables.shun_on_failures=5;
 	variables.shun_recovery_time_sec=10;
 	variables.query_retries_on_failure=1;
+	variables.client_multi_statements=true;
 	variables.connect_retries_on_failure=10;
 	variables.connection_delay_multiplex_ms=0;
 	variables.connection_max_age_ms=0;
@@ -694,6 +696,7 @@ int MySQL_Threads_Handler::get_variable_int(char *name) {
 	if (!strcasecmp(name,"poll_timeout")) return variables.poll_timeout;
 	if (!strcasecmp(name,"poll_timeout_on_failure")) return variables.poll_timeout_on_failure;
 	if (!strcasecmp(name,"stacksize")) return ( stacksize ? stacksize : DEFAULT_STACK_SIZE);
+	if (!strcasecmp(name,"client_multi_statements")) return (int)variables.client_multi_statements;
 	proxy_error("Not existing variable: %s\n", name); assert(0);
 	return 0;
 }
@@ -859,6 +862,9 @@ char * MySQL_Threads_Handler::get_variable(char *name) {	// this is the public f
 		sprintf(intbuf,"%d",variables.shun_on_failures);
 		return strdup(intbuf);
 	}
+	if (!strcasecmp(name,"client_multi_statements")) {
+		return strdup((variables.client_multi_statements ? "true" : "false"));
+	}
 	if (!strcasecmp(name,"connpoll_reset_queue_length")) {
 		sprintf(intbuf,"%d",variables.connpoll_reset_queue_length);
 		return strdup(intbuf);
@@ -1637,6 +1643,17 @@ bool MySQL_Threads_Handler::set_variable(char *name, char *value) {	// this is t
 			return false;
 		}
 	}
+	if (!strcasecmp(name,"client_multi_statements")) {
+		if (strcasecmp(value,"true")==0 || strcasecmp(value,"1")==0) {
+			variables.client_multi_statements=true;
+			return true;
+		}
+		if (strcasecmp(value,"false")==0 || strcasecmp(value,"0")==0) {
+			variables.client_multi_statements=false;
+			return true;
+		}
+		return false;
+	}
 	if (!strcasecmp(name,"connect_retries_on_failure")) {
 		int intv=atoi(value);
 		if (intv >= 0 && intv <= 1000) {
@@ -3381,6 +3398,7 @@ void MySQL_Thread::refresh_variables() {
 	mysql_thread___shun_recovery_time_sec=GloMTH->get_variable_int((char *)"shun_recovery_time_sec");
 	mysql_thread___query_retries_on_failure=GloMTH->get_variable_int((char *)"query_retries_on_failure");
 	mysql_thread___connect_retries_on_failure=GloMTH->get_variable_int((char *)"connect_retries_on_failure");
+	mysql_thread___client_multi_statements=(bool)GloMTH->get_variable_int((char *)"client_multi_statements");
 	mysql_thread___connection_delay_multiplex_ms=GloMTH->get_variable_int((char *)"connection_delay_multiplex_ms");
 	mysql_thread___connection_max_age_ms=GloMTH->get_variable_int((char *)"connection_max_age_ms");
 	mysql_thread___connect_timeout_server=GloMTH->get_variable_int((char *)"connect_timeout_server");

lib/mysql_connection.cpp

@@ -424,7 +424,8 @@ void MySQL_Connection::connect_start() {
 		client_flags += CLIENT_FOUND_ROWS;
 	if (parent->compression)
 		client_flags += CLIENT_COMPRESS;
-	client_flags += CLIENT_MULTI_STATEMENTS; // FIXME: add global variable
+	if (mysql_thread___client_multi_statements)
+		client_flags += CLIENT_MULTI_STATEMENTS;
 	char *auth_password=NULL;
 	if (userinfo->password) {
 		if (userinfo->password[0]=='*') { // we don't have the real password, let's pass sha1