Add an UNDO_LOG_SIZE column to the SESSIONS metadata table, to allow detecting when rogue

sessions are creating large transactions.

h2/src/docsrc/html/changelog.html

@@ -32,6 +32,8 @@ Change Log
     engines on a per-DB basis.
 </li><li>When running the Recover tool on very large (>6G) databases, some statistics were reported with
     negative numbers.
+</li><li>Add an UNDO_LOG_SIZE column to the SESSIONS metadata table, to allow detecting when rogue
+    sessions are creating large transactions.
 </li></ul>
 
 <h2>Version 1.3.173 (2013-07-28)</h2>

h2/src/main/org/h2/engine/Session.java

@@ -1382,6 +1382,10 @@ public class Session extends SessionWithState {
         closeTemporaryResults();
     }
 
+    public int getUndoLogSize() {
+        return undoLog.size();
+    }
+    
     /**
      * Represents a savepoint (a position in a transaction to where one can roll
      * back to).

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

@@ -488,7 +488,8 @@ public class MetaTable extends Table {
                     "USER_NAME",
                     "SESSION_START",
                     "STATEMENT",
-                    "STATEMENT_START"
+                    "STATEMENT_START",
+                    "UNDO_LOG_SIZE"
             );
             break;
         }
@@ -1547,7 +1548,9 @@ public class MetaTable extends Table {
                             // STATEMENT
                             command == null ? null : command.toString(),
                             // STATEMENT_START
-                            new Timestamp(start).toString()
+                            new Timestamp(start).toString(),
+                            // UNDO_LOG_SIZE
+                            "" + s.getUndoLogSize()
                     );
                 }
             }

h2/src/test/org/h2/test/jdbc/TestMetaData.java

@@ -50,6 +50,7 @@ public class TestMetaData extends TestBase {
         testStatic();
         testGeneral();
         testAllowLiteralsNone();
+        testSessions();
     }
 
     private void testColumnResultSetMeta() throws SQLException {
@@ -971,4 +972,24 @@ public class TestMetaData extends TestBase {
         deleteDb("metaData");
     }
 
+    private void testSessions() throws SQLException {
+        Connection conn = getConnection("metaData");
+        conn.setAutoCommit(false);
+        Statement stat = conn.createStatement();
+        stat.execute("create table test(id int)");
+        stat.execute("begin transaction");
+        for (int i = 0; i < 6; i++) {
+            stat.execute("insert into test values (1)");
+        }
+        ResultSet rs = stat.executeQuery("select undo_log_size from INFORMATION_SCHEMA.SESSIONS");
+        rs.next();
+        assertEquals(6, rs.getInt(1));
+        rs.close();
+        stat.execute("commit");
+        rs = stat.executeQuery("select undo_log_size from INFORMATION_SCHEMA.SESSIONS");
+        rs.next();
+        assertEquals(0, rs.getInt(1));
+        conn.close();
+        deleteDb("metaData");
+    }
 }