In debug mode, the handlers for ProxySQL_Statistics are called even if the web interface plugin is not loaded. This way the code can be tested even if the plugin is not loaded. Added new member function ProxySQL_Statistics::knows_variable_name(), which is used to check if a variable_name is in the map. This is useful to do a check before get_variable_id_for_name() in instances where it is undesirable to load or create entries in the lookup table, while keeping direct access to the map private and mutex protected. In ProxySQL_Statistics::get_variable_id_for_name, wrapped the variable_id select code in a lambda so that it could be reused instead of calling sqlite3_last_insert_rowid(), as there were some thread safety concerns which potentially could produce incorrect ids. Changed the insert to use execute() instead of execute_statement() instead, sufficient and simpler. Added error in case the function could not find, load, or generate a new id.

include/ProxySQL_Statistics.hpp

@@ -151,6 +151,10 @@ class ProxySQL_Statistics {
 
 	/** @brief If the variable_name_id_map is empty, then load its contents from all of the history_variables_lookup table records */
 	void load_variable_name_id_map_if_empty();
+
+	/** @return True if the given variable_name is registered in the variable_name_id_map. */
+	bool knows_variable_name(std::string variable_name) const;
+
 	private:
 	/** @brief Map with the key being the variable_name and the value being the variable_id, used for history_mysql_variables data. Matches the history_mysql_variables_lookup. */
 	std::map<std::string, int64_t> variable_name_id_map;

lib/ProxySQL_Admin.cpp

@@ -5081,7 +5081,11 @@ __end_while_pool:
 					SQLite3_result * resultset=MyHGM->SQL3_Get_ConnPool_Stats();
 					if (resultset) {
 						SQLite3_result * resultset2 = NULL;
+					#ifdef DEBUG
+						if (true) {
+					#else
 						if (GloVars.web_interface_plugin) {
+					#endif
 							resultset2 = MyHGM->SQL3_Connection_Pool(false);
 						}
 						GloProxyStats->MyHGM_Handler_sets(resultset, resultset2);

lib/ProxySQL_Statistics.cpp

@@ -644,7 +644,11 @@ void ProxySQL_Statistics::system_memory_sets() {
 
 void ProxySQL_Statistics::MyHGM_Handler_sets(SQLite3_result *resultset1, SQLite3_result *resultset2) {
 	MyHGM_Handler_sets_v1(resultset1);
+#ifdef DEBUG
+	if (resultset2) {
+#else
 	if (GloVars.web_interface_plugin && resultset2) {
+#endif
 		MySQL_Threads_Handler_sets_v2(resultset1);
 		MyHGM_Handler_sets_connection_pool(resultset2);
 	}
@@ -789,7 +793,11 @@ void ProxySQL_Statistics::MyHGM_Handler_sets_v1(SQLite3_result *resultset) {
 
 void ProxySQL_Statistics::MySQL_Threads_Handler_sets(SQLite3_result *resultset) {
 	MySQL_Threads_Handler_sets_v1(resultset);
+#ifdef DEBUG
+	if (true) {
+#else
 	if (GloVars.web_interface_plugin) {
+#endif
 		MySQL_Threads_Handler_sets_v2(resultset);
 	}
 }
@@ -1072,12 +1080,17 @@ void ProxySQL_Statistics::MySQL_Query_Cache_sets(SQLite3_result *resultset) {
 	}
 }
 
+bool ProxySQL_Statistics::knows_variable_name(std::string variable_name) const
+{
+	return (variable_name_id_map.find(variable_name) != variable_name_id_map.end());
+}
+
 int64_t ProxySQL_Statistics::get_variable_id_for_name(std::string variable_name) {
 	lock_guard<mutex> lock(mu);
 
 	int64_t variable_id = -1; // Negative value indicates not yet found.
 
-	if (variable_name_id_map.find(variable_name) != variable_name_id_map.end()) {
+	if (knows_variable_name(variable_name)) {
 		variable_id = variable_name_id_map[variable_name];
 	} else {
 		// No matching variable_id found in map. Try loading from the SQLite lookup table on disk 
@@ -1086,55 +1099,46 @@ int64_t ProxySQL_Statistics::get_variable_id_for_name(std::string variable_name)
 		int affected_rows;
 		char *error = NULL;
 		
-		std::string var_id_query = "SELECT variable_id FROM history_mysql_status_variables_lookup WHERE variable_name=\"" + variable_name + "\"";
-		statsdb_disk->execute_statement(var_id_query.c_str(), &error , &cols , &affected_rows , &result);
+		auto select_var_id = [&]() -> int64_t {
+			string var_id_query = "SELECT variable_id FROM history_mysql_status_variables_lookup WHERE variable_name=\"" + variable_name + "\"";
+			statsdb_disk->execute_statement(var_id_query.c_str(), &error , &cols , &affected_rows , &result);
 
-		// @note: Perhaps a better solution here in case of SQLite errors? Originally considered returning std::optional (but that's c++17) or negative value if not found.
-		// This would also mean having to change the index calculations and prepared statement in MySQL_Threads_Handler_sets_v2() to skip variables with missing ids.
-		// So, for now, this code follows the convention originally used above which exits if there are SQLite errors.
+			if (error) {
+				proxy_error("SQLITE ERROR %s", error);
+				free(error);
+				error = NULL;
+				exit(EXIT_SUCCESS); 
+			} 
+			
+			if (result) {
+				if (result->rows_count > 0) {
+					// matching variable_id for variable_name in lookup table
+					SQLite3_row *r = result->rows[0];
+					return strtoll(r->fields[0], NULL, 10);
+				}
+				delete result;
+				result = NULL;
+			}	
+			return -1;
+		};
 
-		if (error) {
-			proxy_error("SQLITE ERROR %s", error);
-			free(error);
-			error = NULL;
-			exit(EXIT_SUCCESS); 
-		} 
-		
-		if (result) {
-			if (result->rows_count > 0) {
-				// matching variable_id for variable_name in lookup table
-				SQLite3_row *r = result->rows[0];
-				variable_id = strtoll(r->fields[0], NULL, 10);
-			}
-			delete result;
-			result = NULL;
-		}	
+		variable_id = select_var_id(); // Check for variable name present in the lookup
 
 		if (variable_id < 0) {
-			// No match found, create a new record in the lookup table and then return the newly generated id
+			// No match found, create a new record in the lookup table and then select the newly generated id
 			string insert_var_query = "INSERT INTO history_mysql_status_variables_lookup(variable_name) VALUES(\"" + variable_name + "\")";
-			statsdb_disk->execute_statement(insert_var_query.c_str(), &error, &cols, &affected_rows, &result);
-
-			if (error) {
-				proxy_error("SQLITE CRITICAL ERROR: %s", error);
-				if (result)
-					free(result);
-
-				free(error);
-				error = NULL;
-				exit(EXIT_SUCCESS);
-			} else {
-				variable_id = sqlite3_last_insert_rowid(statsdb_disk->get_db());
+			if (statsdb_disk->execute(insert_var_query.c_str())) {
+				variable_id = select_var_id();
 			}
-
-			if (result)
-				free(result);
 		} 
 
 		// Update the map if a lookup record id was found, or if a new record was generated.
-		if (variable_id > 0)
+		if (variable_id > 0) {
 			variable_name_id_map[variable_name] = variable_id;
-
+		} else {
+			proxy_error("CRITIAL ERROR: Statistics could not find or generate variable_id for variable_name: %s", variable_name);
+			exit(EXIT_SUCCESS);
+		}
 	}
 
 	return variable_id;