Merge pull request #9015 from Slach/master

Track the number of MySQL connections

dbms/programs/server/MySQLHandler.h

@@ -2,6 +2,7 @@
 #include <Common/config.h>
 #include <Poco/Net/TCPServerConnection.h>
 #include <Common/getFQDNOrHostName.h>
+#include <Common/CurrentMetrics.h>
 #include <Core/MySQLProtocol.h>
 #include "IServer.h"
 
@@ -9,6 +10,11 @@
 #include <Poco/Net/SecureStreamSocket.h>
 #endif
 
+namespace CurrentMetrics
+{
+    extern const Metric MySQLConnection;
+}
+
 namespace DB
 {
 /// Handler for MySQL wire protocol connections. Allows to connect to ClickHouse using MySQL client.
@@ -20,6 +26,8 @@ public:
     void run() final;
 
 private:
+    CurrentMetrics::Increment metric_increment{CurrentMetrics::MySQLConnection};
+
     /// Enables SSL, if client requested.
     void finishHandshake(MySQLProtocol::HandshakeResponse &);
 

dbms/src/Common/CurrentMetrics.cpp

@@ -15,7 +15,8 @@
     M(DiskSpaceReservedForMerge, "Disk space reserved for currently running background merges. It is slightly more than the total size of currently merging parts.") \
     M(DistributedSend, "Number of connections to remote servers sending data that was INSERTed into Distributed tables. Both synchronous and asynchronous mode.") \
     M(QueryPreempted, "Number of queries that are stopped and waiting due to 'priority' setting.") \
-    M(TCPConnection, "Number of connections to TCP server (clients with native interface)") \
+    M(TCPConnection, "Number of connections to TCP server (clients with native interface), also included server-server distributed query connections") \
+    M(MySQLConnection, "Number of client connections using MySQL protocol") \
     M(HTTPConnection, "Number of connections to HTTP server") \
     M(InterserverConnection, "Number of connections from other replicas to fetch parts") \
     M(OpenFileForRead, "Number of files open for reading") \