Added new variable free_connections_pct

If the number of free connections is greater than free_connections_pct percentage of max_connections for that specific host,
all connections idle for longer than ping_interval_server are closed instead of sending PING

include/MySQL_Thread.h

@@ -253,6 +253,7 @@ class MySQL_Threads_Handler
 		int connect_retries_delay;
 		int connect_timeout_server;
 		int connect_timeout_server_max;
+		int free_connections_pct;
 		bool sessions_sort;
 		char *connect_timeout_server_error;
 		char *default_schema;

include/proxysql_structs.h

@@ -670,6 +670,7 @@ __thread int mysql_thread___max_transaction_time;
 __thread int mysql_thread___max_connections;
 __thread int mysql_thread___default_query_delay;
 __thread int mysql_thread___default_query_timeout;
+__thread int mysql_thread___free_connections_pct;
 __thread int mysql_thread___ping_interval_server;
 __thread int mysql_thread___ping_timeout_server;
 __thread int mysql_thread___connect_retries_on_failure;
@@ -716,6 +717,7 @@ extern __thread int mysql_thread___max_transaction_time;
 extern __thread int mysql_thread___max_connections;
 extern __thread int mysql_thread___default_query_delay;
 extern __thread int mysql_thread___default_query_timeout;
+extern __thread int mysql_thread___free_connections_pct;
 extern __thread int mysql_thread___ping_interval_server;
 extern __thread int mysql_thread___ping_timeout_server;
 extern __thread int mysql_thread___connect_retries_on_failure;

lib/MySQL_HostGroups_Manager.cpp

@@ -552,6 +552,13 @@ int MySQL_HostGroups_Manager::get_multiple_idle_connections(int _hid, unsigned l
 			for (k=0; k<(int)pa->len; k++) {
 				MySQL_Connection *mc=(MySQL_Connection *)pa->index(k);
 				if (mc->last_time_used < _max_last_time_used) {
+					if (pa->len > mysql_thread___free_connections_pct*mysrvc->max_connections/100) {
+						// the idle connection are more than mysql_thread___free_connections_pct of max_connections
+						// we will drop this connection instead of pinging it
+						mc=(MySQL_Connection *)pa->remove_index_fast(k);
+						delete mc;
+						continue;
+					}
 					mc=(MySQL_Connection *)pa->remove_index_fast(k);
 					mysrvc->ConnectionsUsed->add(mc);
 					k--;

lib/MySQL_Thread.cpp

@@ -115,6 +115,7 @@ static char * mysql_thread_variables_names[]= {
 	(char *)"connect_timeout_server_max",
 	(char *)"connect_timeout_server_error",
 	(char *)"default_charset",
+	(char *)"free_connections_pct",
 	(char *)"have_compress",
 	(char *)"interfaces",
 	(char *)"monitor_history",
@@ -170,6 +171,7 @@ MySQL_Threads_Handler::MySQL_Threads_Handler() {
 	variables.connect_retries_on_failure=5;
 	variables.connect_timeout_server=1000;
 	variables.connect_timeout_server_max=10000;
+	variables.free_connections_pct=10;
 	variables.connect_retries_delay=1;
 	variables.monitor_history=600000;
 	variables.monitor_connect_interval=120000;
@@ -327,6 +329,7 @@ int MySQL_Threads_Handler::get_variable_int(char *name) {
 	if (!strcasecmp(name,"max_connections")) return (int)variables.max_connections;
 	if (!strcasecmp(name,"default_query_delay")) return (int)variables.default_query_delay;
 	if (!strcasecmp(name,"default_query_timeout")) return (int)variables.default_query_timeout;
+	if (!strcasecmp(name,"free_connections_pct")) return (int)variables.free_connections_pct;
 	if (!strcasecmp(name,"ping_interval_server")) return (int)variables.ping_interval_server;
 	if (!strcasecmp(name,"ping_timeout_server")) return (int)variables.ping_timeout_server;
 	if (!strcasecmp(name,"have_compress")) return (int)variables.have_compress;
@@ -407,6 +410,10 @@ char * MySQL_Threads_Handler::get_variable(char *name) {	// this is the public f
 		sprintf(intbuf,"%d",variables.connect_timeout_server_max);
 		return strdup(intbuf);
 	}
+	if (!strcasecmp(name,"free_connections_pct")) {
+		sprintf(intbuf,"%d",variables.free_connections_pct);
+		return strdup(intbuf);
+	}
 	if (!strcasecmp(name,"connect_retries_delay")) {
 		sprintf(intbuf,"%d",variables.connect_retries_delay);
 		return strdup(intbuf);
@@ -610,6 +617,15 @@ bool MySQL_Threads_Handler::set_variable(char *name, char *value) {	// this is t
 			return false;
 		}
 	}
+	if (!strcasecmp(name,"free_connections_pct")) {
+		int intv=atoi(value);
+		if (intv >= 0 && intv <= 100) {
+			variables.free_connections_pct=intv;
+			return true;
+		} else {
+			return false;
+		}
+	}
 	if (!strcasecmp(name,"max_connections")) {
 		int intv=atoi(value);
 		if (intv >= 1 && intv <= 1000*1000) {
@@ -1399,6 +1415,7 @@ void MySQL_Thread::refresh_variables() {
 	mysql_thread___connect_retries_on_failure=GloMTH->get_variable_int((char *)"connect_retries_on_failure");
 	mysql_thread___connect_timeout_server=GloMTH->get_variable_int((char *)"connect_timeout_server");
 	mysql_thread___connect_timeout_server_max=GloMTH->get_variable_int((char *)"connect_timeout_server_max");
+	mysql_thread___free_connections_pct=GloMTH->get_variable_int((char *)"free_connections_pct");
 	mysql_thread___connect_retries_delay=GloMTH->get_variable_int((char *)"connect_retries_delay");
 	if (mysql_thread___connect_timeout_server_error) free(mysql_thread___connect_timeout_server_error);
 	mysql_thread___connect_timeout_server_error=GloMTH->get_variable_string((char *)"connect_timeout_server_error");