Clustering: there is now a way to detect which cluster instances are running.

h2/src/docsrc/html/advanced.html

@@ -325,6 +325,18 @@ database that failed, then restart the server that was stopped,
 and re-run the <code>CreateCluster</code> tool.
 </li></ul>
 
+<h3>Detect Which Cluster Instances are Running</h3>
+<p>
+To find out which cluster nodes are currently running, execute the following SQL statement:
+</p>
+<pre>
+SELECT VALUE FROM INFORMATION_SCHEMA.SETTINGS WHERE NAME='CLUSTER'
+</pre>
+<p>
+If the result is <code>''</code> (two single quotes), then the cluster mode is disabled. Otherwise, the list of
+servers is returned, enclosed in single quote. Example: <code>'server1:9191,server2:9191'</code>.
+</p>
+
 <h3>Clustering Algorithm and Limitations</h3>
 <p>
 Read-only queries are only executed against the first cluster node, but all other statements are

h2/src/main/org/h2/table/MetaTable.java

@@ -832,6 +832,7 @@ public class MetaTable extends Table {
                     add(rows, "property." + s, SysProperties.getStringSetting(s, ""));
                 }
             }
+            add(rows, "CLUSTER", database.getCluster());
             add(rows, "EXCLUSIVE", database.getExclusiveSession() == null ? "FALSE" : "TRUE");
             add(rows, "MODE", database.getMode().getName());
             add(rows, "MULTI_THREADED", database.isMultiThreaded() ? "1" : "0");

h2/src/test/org/h2/test/db/TestCluster.java

@@ -56,7 +56,7 @@ public class TestCluster extends TestBase {
             prep.setString(2, "Data" + i);
             prep.executeUpdate();
         }
-        check(conn, len);
+        check(conn, len, "''");
         conn.close();
 
         CreateCluster.main("-urlSource", urlNode1, "-urlTarget",
@@ -81,13 +81,13 @@ public class TestCluster extends TestBase {
 
         // test regular cluster connection
         conn = DriverManager.getConnection("jdbc:h2:tcp://localhost:9191,localhost:9192/test", user, password);
-        check(conn, len);
+        check(conn, len, "'localhost:9191,localhost:9192'");
         conn.close();
 
         // test if only one server is available at the beginning
         n2.stop();
         conn = DriverManager.getConnection("jdbc:h2:tcp://localhost:9191,localhost:9192/test", user, password);
-        check(conn, len);
+        check(conn, len, "''");
         conn.close();
 
         // disable the cluster
@@ -115,13 +115,13 @@ public class TestCluster extends TestBase {
 
         n1 = org.h2.tools.Server.createTcpServer("-tcpPort", "9191", "-baseDir", baseDir + "/node1").start();
         conn = DriverManager.getConnection("jdbc:h2:tcp://localhost:9191/test;CLUSTER=''", user, password);
-        check(conn, len);
+        check(conn, len, "''");
         conn.close();
         n1.stop();
 
         n2 = org.h2.tools.Server.createTcpServer("-tcpPort", "9192", "-baseDir", baseDir + "/node2").start();
         conn = DriverManager.getConnection("jdbc:h2:tcp://localhost:9192/test;CLUSTER=''", user, password);
-        check(conn, len);
+        check(conn, len, "''");
         conn.createStatement().execute("SELECT * FROM A");
         conn.close();
         n2.stop();
@@ -133,7 +133,7 @@ public class TestCluster extends TestBase {
         DeleteDbFiles.main("-dir", baseDir + "/node2", "-quiet");
     }
 
-    private void check(Connection conn, int len) throws SQLException {
+    private void check(Connection conn, int len, String expectedCluster) throws SQLException {
         PreparedStatement prep = conn.prepareStatement("SELECT * FROM TEST WHERE ID=?");
         for (int i = 0; i < len; i++) {
             prep.setInt(1, i);
@@ -142,6 +142,11 @@ public class TestCluster extends TestBase {
             assertEquals("Data" + i, rs.getString(2));
             assertFalse(rs.next());
         }
+        ResultSet rs = conn.createStatement().executeQuery(
+                "SELECT VALUE FROM INFORMATION_SCHEMA.SETTINGS WHERE NAME='CLUSTER'");
+        rs.next();
+        String cluster = rs.getString(1);
+        assertEquals(expectedCluster, cluster);
     }
 
 }