From 14e38e4e087efc5488e9319e5bae2d25e6192fd2 Mon Sep 17 00:00:00 2001
From: Esa Korhonen <esa.korhonen@mariadb.com>
Date: Mon, 12 Nov 2018 12:36:30 +0200
Subject: [PATCH] MXS-2158 Return true if update_gtids() succeeds, even if no
 data is returned

Previously, if the server had no gtid:s, the method would fail leading to
a confusing error message. This could even totally stop the monitor from working
if a recent server version (10.X) did not have any gtid events.
---
 .../monitor/mariadbmon/mariadbserver.cc       | 45 +++++++++++--------
 .../monitor/mariadbmon/mariadbserver.hh       |  2 +-
 2 files changed, 27 insertions(+), 20 deletions(-)

diff --git a/server/modules/monitor/mariadbmon/mariadbserver.cc b/server/modules/monitor/mariadbmon/mariadbserver.cc
index 3c0329c95..0ef954c2b 100644
--- a/server/modules/monitor/mariadbmon/mariadbserver.cc
+++ b/server/modules/monitor/mariadbmon/mariadbserver.cc
@@ -376,32 +376,39 @@ bool MariaDBServer::update_gtids(string* errmsg_out)
 
     bool rval = false;
     auto result = execute_query(query, errmsg_out);
-    if (result.get() != NULL && result->next_row())
+    if (result.get() != NULL)
     {
-        auto current_str = result->get_string(i_current_pos);
-        auto binlog_str = result->get_string(i_binlog_pos);
-        bool current_ok = false;
-        if (current_str.empty())
+        rval = true;
+        if (result->next_row())
         {
-            m_gtid_current_pos = GtidList();
+            // Query returned at least some data.
+            auto current_str = result->get_string(i_current_pos);
+            auto binlog_str = result->get_string(i_binlog_pos);
+            if (current_str.empty())
+            {
+                m_gtid_current_pos = GtidList();
+            }
+            else
+            {
+                m_gtid_current_pos = GtidList::from_string(current_str);
+            }
+
+            if (binlog_str.empty())
+            {
+                m_gtid_binlog_pos = GtidList();
+            }
+            else
+            {
+                m_gtid_binlog_pos = GtidList::from_string(binlog_str);
+            }
         }
         else
         {
-            m_gtid_current_pos = GtidList::from_string(current_str);
-            current_ok = !m_gtid_current_pos.empty();
-        }
-
-        if (binlog_str.empty())
-        {
+            // Query succeeded but returned 0 rows. This means that the server has no gtid:s.
+            m_gtid_current_pos = GtidList();
             m_gtid_binlog_pos = GtidList();
         }
-        else
-        {
-            m_gtid_binlog_pos = GtidList::from_string(binlog_str);
-        }
-
-        rval = current_ok;
-    }
+    } // If query failed, do not update gtid:s.
     return rval;
 }
 
diff --git a/server/modules/monitor/mariadbmon/mariadbserver.hh b/server/modules/monitor/mariadbmon/mariadbserver.hh
index 94bf233aa..c35d4b016 100644
--- a/server/modules/monitor/mariadbmon/mariadbserver.hh
+++ b/server/modules/monitor/mariadbmon/mariadbserver.hh
@@ -202,7 +202,7 @@ public:
      * Query gtid_current_pos and gtid_binlog_pos and save the values to the server.
      *
      * @param errmsg_out Where to store an error message if query fails. Can be null.
-     * @return True if successful
+     * @return True if query succeeded
      */
     bool update_gtids(std::string* errmsg_out = NULL);