[mysql] fix innodb engine check.

[mysql] if the version is too old, the stats will probable be unavailable anyways.

[mysql] disable innodb metrics, respond better to unavailable innodb metrics.

[mysql] catch NotSupportedError - possible exception when querying older MySQLs.

[mysql] adding flag description to yaml, cleaning query.

checks.d/mysql.py

@@ -410,7 +410,7 @@ def _collect_metrics(self, host, db, tags, options, queries):
         results = self._get_stats_from_status(db)
         results.update(self._get_stats_from_variables(db))
 
-        if self._is_innodb_engine_enabled(db):
+        if (not _is_affirmative(options.get('disable_innodb_metrics', False)) and self._is_innodb_engine_enabled(db)):
             results.update(self._get_stats_from_innodb_status(db))
 
             innodb_keys = [
@@ -806,13 +806,18 @@ def _is_innodb_engine_enabled(self, db):
         # Whether InnoDB engine is available or not can be found out either
         # from the output of SHOW ENGINES or from information_schema.ENGINES
         # table. Later is choosen because that involves no string parsing.
-        with closing(db.cursor()) as cursor:
-            cursor.execute(
-                "select engine from information_schema.ENGINES where engine='InnoDB'")
+        try:
+            with closing(db.cursor()) as cursor:
+                cursor.execute(
+                    "select engine from information_schema.ENGINES where engine='InnoDB' and \
+                    support != 'no' and support != 'disabled'"
+                )
 
-            return_val = True if cursor.rowcount > 0 else False
+                return (cursor.rowcount > 0)
 
-            return return_val
+        except (pymysql.err.InternalError, pymysql.err.OperationalError, pymysql.err.NotSupportedError) as e:
+            self.warning("Possibly innodb stats unavailable - error querying engines table: %s" % str(e))
+            return False
 
     def _get_replica_stats(self, db):
         try:
@@ -864,8 +869,9 @@ def _get_stats_from_innodb_status(self, db):
                 cursor.execute("SHOW /*!50000 ENGINE*/ INNODB STATUS")
                 innodb_status = cursor.fetchone()
                 innodb_status_text = innodb_status[2]
-        except (pymysql.err.InternalError, pymysql.err.OperationalError) as e:
-            self.warning("Privilege error accessing the INNODB status tables (must grant PROCESS): %s" % str(e))
+        except (pymysql.err.InternalError, pymysql.err.OperationalError, pymysql.err.NotSupportedError) as e:
+            self.warning("Privilege error or engine unavailable accessing the INNODB status \
+                         tables (must grant PROCESS): %s" % str(e))
             return {}
 
         results = defaultdict(int)

conf.d/mysql.yaml.example

@@ -17,7 +17,11 @@ instances:
     #   extra_innodb_metrics: true
     #   extra_performance_metrics: true
     #   schema_size_metrics: false
+    #   disable_innodb_metrics: false
     #
+    #     NOTE: disable_innodb_metrics should only be used by users with older (unsupported) versions of
+    #           MySQL who do not run/have innodb engine support and may experiment issue otherwise.
+    #           Should this flag be enabled you will only receive a small subset of metrics.
     #
     #     NOTE: extra_performance_metrics will only be reported if `performance_schema` is enabled
     #           in the MySQL instance and if the version for that instance is >= 5.6.0