Merge pull request #3976 from sysown/v2.x-3928

Fix isolation level in AWS Aurora

lib/MySQL_Session.cpp

@@ -2478,8 +2478,24 @@ bool MySQL_Session::handler_again___status_SETTING_GENERIC_VARIABLE(int *_rc, co
 			else {
 				sprintf(query,q,"tx_isolation", var_value);
 			}
-		}
-		else {
+		} else if (strncasecmp("aurora_read_replica_read_committed", var_name, 34) == 0) {
+			// If aurora_read_replica_read_committed is set, isolation level is
+			// internally reset so that it will be set again.
+			// This solves the weird behavior in AWS Aurora related to isolation level
+			// as described in
+			// https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/AuroraMySQL.Reference.html#AuroraMySQL.Reference.IsolationLevels
+			// Basically, to change isolation level you must first set
+			// aurora_read_replica_read_committed , and then isolation level
+			MySQL_Connection *beconn = mybe->server_myds->myconn;
+			if (beconn->var_hash[SQL_ISOLATION_LEVEL] != 0) {
+				beconn->var_hash[SQL_ISOLATION_LEVEL] = 0;
+				if (beconn->variables[SQL_ISOLATION_LEVEL].value) {
+					free(beconn->variables[SQL_ISOLATION_LEVEL].value);
+					beconn->variables[SQL_ISOLATION_LEVEL].value = NULL;
+				}
+			}
+			sprintf(query,q,var_name, var_value);
+		} else {
 			sprintf(query,q,var_name, var_value);
 		}
 		query_length=strlen(query);