doc: Warning about add cgroup kernel issue to resource group docs. (#3492)

* doc: Warning about add cgroup kernel issue to resource group docs.

* docs: fix typo

gpdb-doc/dita/admin_guide/wlmgmt.xml

@@ -11,71 +11,83 @@
       amount of memory used to execute a query, and the relative amount of CPU devoted to processing
       a query. Greenplum Database provides two schemes to manage resources - Resource Queues and
       Resource Groups.</p>
-      <note type="warning">Resource groups are an experimental feature and are not intended for use
-      in a production environment. Experimental features are subject to change without notice in
-      future releases.</note>
+    <note type="warning">Resource groups are an experimental feature and are not intended for use in
+      a production environment. Experimental features are subject to change without notice in future
+        releases.<p>Significant <ph otherprops="pivotal">Pivotal </ph>Greenplum Database performance
+        degradation has been observed when enabling resource group-based workload management on <ph
+          otherprops="pivotal">supported versions of </ph>RedHat 6.x, CentOS 6.x, and SuSE 11
+        systems. The issue is due to a Linux cgroup kernel bug. The kernel bug has been fixed on
+        CentOS 7.x and Red Hat 7.x systems. </p></note>
     <p>Either the resource queue or the resource group management scheme can be active in Greenplum
       Database; both schemes cannot be active at the same time.</p>
     <p>Resource queues are enabled by default when you install your Greenplum Database cluster.
       While you can create and assign resource groups when resource queues are active, you must
       explicitly enable resource groups to start using that management scheme.</p>
 
-    <p>The following table summarizes some of the differences between Resource Queues and Resource Groups.</p>
-     <table id="queue_group_compare">
-        <tgroup cols="3">
-          <colspec colnum="1" colname="col1" colwidth="1*"/>
-          <colspec colnum="2" colname="col2" colwidth="1*"/>
-          <colspec colnum="3" colname="col3" colwidth="1*"/>
-          <thead>
-            <row>
-              <entry colname="col1">Metric</entry>
-              <entry colname="col2">Resource Queues</entry>
-              <entry colname="col3">Resource Groups</entry>
-            </row>
-          </thead>
-          <tbody>
-            <row>
-              <entry colname="col1">Concurrency</entry>
-              <entry colname="col2">Managed at the query level</entry>
-              <entry colname="col3">Managed at the transaction level</entry>
-            </row>
-            <row>
-              <entry colname="col1">CPU</entry>
-              <entry colname="col2">Specify query priority</entry>
-              <entry colname="col3">Specify percentage of CPU resources; uses Linux Control Groups</entry>
-            </row>
-            <row>
-              <entry colname="col1">Memory</entry>
-              <entry colname="col2">Managed at the queue and operator level; users can over-subscribe</entry>
-              <entry colname="col3">Managed at the transaction level, with enhanced allocation and tracking; users cannot over-subscribe</entry>
-            </row>
-            <row>
-              <entry colname="col1">Memory Isolation</entry>
-              <entry colname="col2">None</entry>
-              <entry colname="col3">Memory is isolated between resource groups and between transactions within the same resource group</entry>
-            </row>
-            <row>
-              <entry colname="col1">Users</entry>
-              <entry colname="col2">Limits are applied only to non-admin users</entry>
-              <entry colname="col3">Limits are applied to <codeph>SUPERUSER</codeph> and non-admin users alike</entry>
-            </row>
-            <row>
-              <entry colname="col1">Queueing</entry>
-              <entry colname="col2">Queue only when no slot available</entry>
-              <entry colname="col3">Queue when no slot is available or not enough available memory</entry>
-            </row>
-            <row>
-              <entry colname="col1">Query Failure</entry>
-              <entry colname="col2">Query may fail immediately if not enough memory</entry>
-              <entry colname="col3">Query may fail after reaching transaction memory limit</entry>
-            </row>
-            <row>
-              <entry colname="col1">Limit Bypass</entry>
-              <entry colname="col2">Limits are not enforced for <codeph>SUPERUSER</codeph> roles and certain operators and functions</entry>
-              <entry colname="col3">No limit bypass cases</entry>
-            </row>
-          </tbody>
-        </tgroup>
-      </table>
-    </body>
-  </topic>
+    <p>The following table summarizes some of the differences between Resource Queues and Resource
+      Groups.</p>
+    <table id="queue_group_compare">
+      <tgroup cols="3">
+        <colspec colnum="1" colname="col1" colwidth="1*"/>
+        <colspec colnum="2" colname="col2" colwidth="1*"/>
+        <colspec colnum="3" colname="col3" colwidth="1*"/>
+        <thead>
+          <row>
+            <entry colname="col1">Metric</entry>
+            <entry colname="col2">Resource Queues</entry>
+            <entry colname="col3">Resource Groups</entry>
+          </row>
+        </thead>
+        <tbody>
+          <row>
+            <entry colname="col1">Concurrency</entry>
+            <entry colname="col2">Managed at the query level</entry>
+            <entry colname="col3">Managed at the transaction level</entry>
+          </row>
+          <row>
+            <entry colname="col1">CPU</entry>
+            <entry colname="col2">Specify query priority</entry>
+            <entry colname="col3">Specify percentage of CPU resources; uses Linux Control
+              Groups</entry>
+          </row>
+          <row>
+            <entry colname="col1">Memory</entry>
+            <entry colname="col2">Managed at the queue and operator level; users can
+              over-subscribe</entry>
+            <entry colname="col3">Managed at the transaction level, with enhanced allocation and
+              tracking; users cannot over-subscribe</entry>
+          </row>
+          <row>
+            <entry colname="col1">Memory Isolation</entry>
+            <entry colname="col2">None</entry>
+            <entry colname="col3">Memory is isolated between resource groups and between
+              transactions within the same resource group</entry>
+          </row>
+          <row>
+            <entry colname="col1">Users</entry>
+            <entry colname="col2">Limits are applied only to non-admin users</entry>
+            <entry colname="col3">Limits are applied to <codeph>SUPERUSER</codeph> and non-admin
+              users alike</entry>
+          </row>
+          <row>
+            <entry colname="col1">Queueing</entry>
+            <entry colname="col2">Queue only when no slot available</entry>
+            <entry colname="col3">Queue when no slot is available or not enough available
+              memory</entry>
+          </row>
+          <row>
+            <entry colname="col1">Query Failure</entry>
+            <entry colname="col2">Query may fail immediately if not enough memory</entry>
+            <entry colname="col3">Query may fail after reaching transaction memory limit</entry>
+          </row>
+          <row>
+            <entry colname="col1">Limit Bypass</entry>
+            <entry colname="col2">Limits are not enforced for <codeph>SUPERUSER</codeph> roles and
+              certain operators and functions</entry>
+            <entry colname="col3">No limit bypass cases</entry>
+          </row>
+        </tbody>
+      </tgroup>
+    </table>
+  </body>
+</topic>