New experimental system property "h2.modifyOnWrite".

h2/src/main/org/h2/command/Command.java

@@ -174,7 +174,9 @@ public abstract class Command implements CommandInterface {
         session.waitIfExclusiveModeEnabled();
         boolean writing = !isReadOnly();
         if (writing) {
-            database.beforeWriting();
+            while (!database.beforeWriting()) {
+                // wait
+            }
         }
         synchronized (sync) {
             session.setCurrentCommand(this);
@@ -208,9 +210,14 @@ public abstract class Command implements CommandInterface {
         Object sync = database.isMultiThreaded() ? (Object) session : (Object) database;
         session.waitIfExclusiveModeEnabled();
         boolean callStop = true;
-        database.beforeWriting();
+        boolean writing = !isReadOnly();
+        if (writing) {
+            while (!database.beforeWriting()) {
+                // wait
+            }
+        }
         synchronized (sync) {
-            int rollback = session.getLogId();
+            int rollback = session.getUndoLogPos();
             session.setCurrentCommand(this);
             try {
                 while (true) {
@@ -248,7 +255,9 @@ public abstract class Command implements CommandInterface {
                         stop();
                     }
                 } finally {
-                    database.afterWriting();
+                    if (writing) {
+                        database.afterWriting();
+                    }
                 }
             }
         }

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

@@ -61,6 +61,11 @@ public class Constants {
      */
     public static final int TCP_PROTOCOL_VERSION_9 = 9;
 
+    /**
+     * The TCP protocol version number 10.
+     */
+    public static final int TCP_PROTOCOL_VERSION_10 = 10;
+
     /**
      * The major version of this database.
      */

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

@@ -542,7 +542,7 @@ public class Session extends SessionWithState {
         }
     }
 
-    public int getLogId() {
+    public int getUndoLogPos() {
         return undoLog.size();
     }
 
@@ -755,7 +755,7 @@ public class Session extends SessionWithState {
         if (savepoints == null) {
             savepoints = database.newStringMap();
         }
-        savepoints.put(name, getLogId());
+        savepoints.put(name, getUndoLogPos());
     }
 
     /**

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

@@ -67,6 +67,13 @@ public interface SessionInterface extends Closeable {
      */
     DataHandler getDataHandler();
 
+    /**
+     * Get the undo log position.
+     *
+     * @return the position (0 means no pending transaction)
+     */
+    int getUndoLogPos();
+
     /**
      * Cancel the current or next command (called when closing a connection).
      */

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

@@ -55,6 +55,7 @@ public class SessionRemote extends SessionWithState implements DataHandler {
     public static final int SESSION_CANCEL_STATEMENT = 13;
     public static final int SESSION_CHECK_KEY = 14;
     public static final int SESSION_SET_AUTOCOMMIT = 15;
+    public static final int SESSION_UNDO_LOG_POS = 16;
 
     public static final int STATUS_ERROR = 0;
     public static final int STATUS_OK = 1;
@@ -94,7 +95,7 @@ public class SessionRemote extends SessionWithState implements DataHandler {
         trans.setSSL(ci.isSSL());
         trans.init();
         trans.writeInt(Constants.TCP_PROTOCOL_VERSION_6);
-        trans.writeInt(Constants.TCP_PROTOCOL_VERSION_9);
+        trans.writeInt(Constants.TCP_PROTOCOL_VERSION_10);
         trans.writeString(db);
         trans.writeString(ci.getOriginalURL());
         trans.writeString(ci.getUserName());
@@ -120,6 +121,24 @@ public class SessionRemote extends SessionWithState implements DataHandler {
         return trans;
     }
 
+    public int getUndoLogPos() {
+        if (clientVersion < Constants.TCP_PROTOCOL_VERSION_10) {
+            return 1;
+        }
+        for (int i = 0, count = 0; i < transferList.size(); i++) {
+            Transfer transfer = transferList.get(i);
+            try {
+                traceOperation("SESSION_UNDO_LOG_POS", 0);
+                transfer.writeInt(SessionRemote.SESSION_UNDO_LOG_POS);
+                done(transfer);
+                return transfer.readInt();
+            } catch (IOException e) {
+                removeServer(e, i--, ++count);
+            }
+        }
+        return 1;
+    }
+
     public void cancel() {
         // this method is called when closing the connection
         // the statement that is currently running is not canceled in this case
@@ -482,6 +501,7 @@ public class SessionRemote extends SessionWithState implements DataHandler {
     }
 
     public void close() {
+        RuntimeException closeError = null;
         if (transferList != null) {
             synchronized (this) {
                 for (Transfer transfer : transferList) {
@@ -490,6 +510,9 @@ public class SessionRemote extends SessionWithState implements DataHandler {
                         transfer.writeInt(SessionRemote.SESSION_CLOSE);
                         done(transfer);
                         transfer.close();
+                    } catch (RuntimeException e) {
+                        trace.error(e, "close");
+                        closeError = e;
                     } catch (Exception e) {
                         trace.error(e, "close");
                     }
@@ -502,6 +525,9 @@ public class SessionRemote extends SessionWithState implements DataHandler {
             embedded.close();
             embedded = null;
         }
+        if (closeError != null) {
+            throw closeError;
+        }
     }
 
     public Trace getTrace() {

h2/src/main/org/h2/jdbc/JdbcConnection.java

@@ -345,15 +345,17 @@ public class JdbcConnection extends TraceObject implements Connection {
                 try {
                     if (!session.isClosed()) {
                         try {
-                            // roll back unless that would require to re-connect
-                            // (the transaction can't be rolled back after re-connecting)
-                            if (!session.isReconnectNeeded(true)) {
-                                try {
-                                    rollbackInternal();
-                                } catch (DbException e) {
-                                    // ignore if the connection is broken right now
-                                    if (e.getErrorCode() != ErrorCode.CONNECTION_BROKEN_1) {
-                                        throw e;
+                            if (session.getUndoLogPos() != 0) {
+                                // roll back unless that would require to re-connect
+                                // (the transaction can't be rolled back after re-connecting)
+                                if (!session.isReconnectNeeded(true)) {
+                                    try {
+                                        rollbackInternal();
+                                    } catch (DbException e) {
+                                        // ignore if the connection is broken right now
+                                        if (e.getErrorCode() != ErrorCode.CONNECTION_BROKEN_1) {
+                                            throw e;
+                                        }
                                     }
                                 }
                                 session.afterWriting();

h2/src/main/org/h2/server/TcpServerThread.java

@@ -71,12 +71,12 @@ public class TcpServerThread implements Runnable {
                 int minClientVersion = transfer.readInt();
                 if (minClientVersion < Constants.TCP_PROTOCOL_VERSION_6) {
                     throw DbException.get(ErrorCode.DRIVER_VERSION_ERROR_2, "" + clientVersion, "" + Constants.TCP_PROTOCOL_VERSION_6);
-                } else if (minClientVersion > Constants.TCP_PROTOCOL_VERSION_9) {
-                    throw DbException.get(ErrorCode.DRIVER_VERSION_ERROR_2, "" + clientVersion, "" + Constants.TCP_PROTOCOL_VERSION_9);
+                } else if (minClientVersion > Constants.TCP_PROTOCOL_VERSION_10) {
+                    throw DbException.get(ErrorCode.DRIVER_VERSION_ERROR_2, "" + clientVersion, "" + Constants.TCP_PROTOCOL_VERSION_10);
                 }
                 int maxClientVersion = transfer.readInt();
-                if (maxClientVersion >= Constants.TCP_PROTOCOL_VERSION_9) {
-                    clientVersion = Constants.TCP_PROTOCOL_VERSION_9;
+                if (maxClientVersion >= Constants.TCP_PROTOCOL_VERSION_10) {
+                    clientVersion = Constants.TCP_PROTOCOL_VERSION_10;
                 } else {
                     clientVersion = minClientVersion;
                 }
@@ -149,20 +149,32 @@ public class TcpServerThread implements Runnable {
 
     private void closeSession() {
         if (session != null) {
+            RuntimeException closeError = null;
             try {
                 Command rollback = session.prepareLocal("ROLLBACK");
                 rollback.executeUpdate();
+            } catch (RuntimeException e) {
+                closeError = e;
+                server.traceError(e);
             } catch (Exception e) {
                 server.traceError(e);
             }
             try {
                 session.close();
                 server.removeConnection(threadId);
+            } catch (RuntimeException e) {
+                if (closeError == null) {
+                    closeError = e;
+                    server.traceError(e);
+                }
             } catch (Exception e) {
                 server.traceError(e);
             } finally {
                 session = null;
             }
+            if (closeError != null) {
+                throw closeError;
+            }
         }
     }
 
@@ -173,12 +185,13 @@ public class TcpServerThread implements Runnable {
         try {
             stop = true;
             closeSession();
-            transfer.close();
-            trace("Close");
         } catch (Exception e) {
             server.traceError(e);
+        } finally {
+            transfer.close();
+            trace("Close");
+            server.remove(this);
         }
-        server.remove(this);
     }
 
     private void sendError(Throwable t) {
@@ -241,6 +254,7 @@ public class TcpServerThread implements Runnable {
             break;
         }
         case SessionRemote.SESSION_CLOSE: {
+            stop = true;
             closeSession();
             transfer.writeInt(SessionRemote.STATUS_OK).flush();
             close();
@@ -364,6 +378,11 @@ public class TcpServerThread implements Runnable {
             transfer.writeInt(SessionRemote.STATUS_OK).flush();
             break;
         }
+        case SessionRemote.SESSION_UNDO_LOG_POS: {
+            transfer.writeInt(SessionRemote.STATUS_OK).
+                writeInt(session.getUndoLogPos()).flush();
+            break;
+        }
         default:
             trace("Unknown operation: " + operation);
             closeSession();

h2/src/main/org/h2/store/FileLock.java

@@ -224,7 +224,7 @@ public class FileLock implements Runnable {
             transfer.setSocket(socket);
             transfer.init();
             transfer.writeInt(Constants.TCP_PROTOCOL_VERSION_6);
-            transfer.writeInt(Constants.TCP_PROTOCOL_VERSION_9);
+            transfer.writeInt(Constants.TCP_PROTOCOL_VERSION_10);
             transfer.writeString(null);
             transfer.writeString(null);
             transfer.writeString(id);