Prevent circular fetches due for 'test_unshun_algorithm-t'

Test is now aware of 'cluster_mysql_servers_sync_algorithm'. In case of
'runtime_mysql_servers' propagation, the test disables monitoring since
it creates servers in hostgroups with active monitoring, if config
doesn't allows 'runtime' propagation, the test assumes everything will
just work. This should be a common pattern for tests creating fake
servers.

test/tap/tests/test_unshun_algorithm-t.cpp

@@ -59,12 +59,12 @@
 
 #include <cstring>
 #include <unistd.h>
-#include <vector>
 #include <string>
 #include <stdio.h>
+#include <utility>
+#include <vector>
 
 #include "mysql.h"
-#include "mysqld_error.h"
 
 #include "proxysql_utils.h"
 #include "tap.h"
@@ -74,8 +74,11 @@
 const uint32_t SHUN_RECOVERY_TIME = 1;
 const uint32_t VALID_RANGE = 1;
 const uint32_t SERVERS_COUNT = 10;
+const uint32_t SYNC_TIMEOUT = 10;
 
+using std::pair;
 using std::string;
+using std::vector;
 
 int shunn_server(MYSQL* proxysql_admin, uint32_t i, uint32_t j) {
 	std::string t_simulator_error_query { "PROXYSQL_SIMULATOR mysql_error %d 127.0.0.1:330%d 1234" };
@@ -426,8 +429,43 @@ int main(int argc, char** argv) {
 	}
 
 	// Disable Monitor for the following tests
-	MYSQL_QUERY(proxysql_admin, "SET mysql-monitor_enabled=0");
-	MYSQL_QUERY(proxysql_admin, "LOAD MYSQL VARIABLES TO RUNTIME");
+	MYSQL_QUERY_T(proxysql_admin, "SET mysql-monitor_enabled=0");
+	MYSQL_QUERY_T(proxysql_admin, "LOAD MYSQL VARIABLES TO RUNTIME");
+
+	// We need to wait for synchronization in case 'admin-cluster_mysql_servers_sync_algorithm=1' to prevent
+	// circular fetches. If config is set to '2' we DO NOT wait, as circular fetches shouldn't be possible,
+	// this way a misbehavior **could** be detected by the test. We do not enforce failure either.
+	{
+		const char sync_algo_query[] {
+			"SELECT variable_value FROM global_variables"
+				" WHERE variable_name='admin-cluster_mysql_servers_sync_algorithm'",
+		};
+		ext_val_t<int32_t> servers_sync_algo { mysql_query_ext_val(proxysql_admin, sync_algo_query, 1) };
+		if (servers_sync_algo.err != EXIT_SUCCESS) {
+			const string err { get_ext_val_err(proxysql_admin, servers_sync_algo) };
+			diag("Failed getting variable   query:`%s`, err:`%s`", sync_algo_query, err.c_str());
+			goto cleanup;
+		}
+
+		// NOTE: '3' is a configuration thought for replicas, this test assumes it's connecting to a
+		// primary, so the same protection should be applied.
+		if (servers_sync_algo.val == 1 || servers_sync_algo.val == 3) {
+			const pair<int,vector<srv_addr_t>> core_nodes { fetch_cluster_nodes(proxysql_admin) };
+			if (core_nodes.first) {
+				diag("Cluster node fetching failed with mysql_errno=%d", core_nodes.first);
+				goto cleanup;
+			}
+
+			const char sync_query[] {
+				"SELECT CASE WHEN "
+					"(SELECT variable_value FROM runtime_global_variables WHERE"
+						" variable_name='mysql-monitor_enabled')='false'"
+					" THEN 1 ELSE 0 END"
+			};
+			int check_res = check_nodes_sync(cl, core_nodes.second, sync_query, SYNC_TIMEOUT);
+			if (check_res != EXIT_SUCCESS) { goto cleanup; }
+		}
+	}
 
 	{
 		int simulator_err = test_proxysql_simulator_error(proxysql_admin);