Revert to Command execution at least under a session lock

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

@@ -185,7 +185,7 @@ public abstract class Command implements CommandInterface {
         startTimeNanos = 0;
         long start = 0;
         Database database = session.getDatabase();
-        Object sync = database.getMvStore() != null ? null : database.isMultiThreaded() ? session : database;
+        Object sync = database.isMultiThreaded() || database.getMvStore() != null ? session : database;
         session.waitIfExclusiveModeEnabled();
         boolean callStop = true;
         boolean writing = !isReadOnly();
@@ -201,14 +201,10 @@ public abstract class Command implements CommandInterface {
                 database.checkPowerOff();
                 try {
                     ResultInterface result;
-                    if (sync != null) {
                     //noinspection SynchronizationOnLocalVariableOrMethodParameter
                     synchronized (sync) {
                         result = query(maxrows);
                     }
-                    } else {
-                        result = query(maxrows);
-                    }
                     callStop = !result.isLazy();
                     return result;
                 } catch (DbException e) {
@@ -250,7 +246,7 @@ public abstract class Command implements CommandInterface {
     public ResultWithGeneratedKeys executeUpdate(Object generatedKeysRequest) {
         long start = 0;
         Database database = session.getDatabase();
-        Object sync = database.getMvStore() != null ? null : database.isMultiThreaded() ? session : database;
+        Object sync = database.isMultiThreaded() || database.getMvStore() != null ? session : database;
         session.waitIfExclusiveModeEnabled();
         boolean callStop = true;
         boolean writing = !isReadOnly();
@@ -267,14 +263,10 @@ public abstract class Command implements CommandInterface {
                 database.checkPowerOff();
                 try {
                     int updateCount;
-                    if (sync != null) {
                     //noinspection SynchronizationOnLocalVariableOrMethodParameter
                     synchronized (sync) {
                         updateCount = update();
                     }
-                    } else {
-                        updateCount = update();
-                    }
                     if (!Boolean.FALSE.equals(generatedKeysRequest)) {
                         return new ResultWithGeneratedKeys.WithKeys(updateCount,
                                 session.getGeneratedKeys().getKeys(session));