MONDRIAN Prevent the dynamic datasource servlet from reading the file…

… at every servlet request. Now does it at every X time interval instead.

[git-p4: depot-paths = "//open/mondrian-release/3.2/": change = 13904]

src/main/mondrian/xmla/impl/DynamicDatasourceXmlaServlet.java

@@ -33,12 +33,39 @@ public class DynamicDatasourceXmlaServlet extends DefaultXmlaServlet {
     protected URL dataSourcesConfigUrl;
     protected String lastDataSourcesConfigString;
 
+    public final static String SCHEMA_UPDATE_DELAY = "SCHEMA_UPDATE_DELAY";
+    /**
+     * Contains the last timestamp in milis when the
+     * schema was checked for updates.
+     */
+    protected long lastUpdate = System.currentTimeMillis();
+
+    /**
+     * Interval, in miliseconds, at which to check for
+     * an updated schema. This is actually a TTL value checked
+     * at each post request. There are no background tasks running.
+     */
+    protected long updateDelay = 3000;
+
+    @Override
+    public void init() throws ServletException {
+        super.init();
+        if (getInitParameter(SCHEMA_UPDATE_DELAY) != null) {
+            updateDelay = Long.valueOf(
+                getInitParameter(SCHEMA_UPDATE_DELAY));
+        }
+    }
+
     protected void doPost(
         HttpServletRequest request,
         HttpServletResponse response)
         throws ServletException, IOException
     {
-        reloadDataSources();
+        // Check if an update is necessary
+        if (lastUpdate + updateDelay >= System.currentTimeMillis()) {
+            lastUpdate = System.currentTimeMillis();
+            reloadDataSources();
+        }
         super.doPost(request, response);
     }