cancel ids release on rollback

address review comments

h2/src/main/org/h2/command/dml/Insert.java

@@ -154,7 +154,6 @@ public class Insert extends Prepared implements ResultTarget {
             Mode mode = session.getDatabase().getMode();
             int columnLen = columns.length;
             for (int x = 0; x < listSize; x++) {
-                session.startStatementWithinTransaction();
                 generatedKeys.nextRow();
                 Row newRow = table.getTemplateRow();
                 Expression[] expr = list.get(x);

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

@@ -1084,7 +1084,7 @@ public class Database implements DataHandler {
                 // otherwise it might be re-used prematurely, and it would make
                 // rollback impossible or lead to MVMaps name collision,
                 // so until then ids are accumulated within session
-                session.releaseDatabaseObjectId(id);
+                session.scheduleDatabaseObjectIdForRelease(id);
             } else {
                 // but PageStore, on the other hand, for reasons unknown to me,
                 // requires immediate id release

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

@@ -166,7 +166,7 @@ public class Session extends SessionWithState implements TransactionStore.Rollba
     /**
      * Set of database object ids to be released at the end of transaction
      */
-    private final BitSet idsToRelease = new BitSet();
+    private BitSet idsToRelease;
 
 
     public Session(Database database, User user, int id) {
@@ -634,7 +634,15 @@ public class Session extends SessionWithState implements TransactionStore.Rollba
         return command;
     }
 
-    void releaseDatabaseObjectId(int id) {
+    /**
+     * Arranges for the specified database object id to be released
+     * at the end of the current transaction.
+     * @param id to be scheduled
+     */
+    void scheduleDatabaseObjectIdForRelease(int id) {
+        if (idsToRelease == null) {
+            idsToRelease = new BitSet();
+        }
         idsToRelease.set(id);
     }
 
@@ -757,8 +765,10 @@ public class Session extends SessionWithState implements TransactionStore.Rollba
             removeLobMap = null;
         }
         unlockAll();
+        if (idsToRelease != null) {
             database.releaseDatabaseObjectIds(idsToRelease);
-        idsToRelease.clear();
+            idsToRelease = null;
+        }
     }
 
     /**
@@ -775,6 +785,7 @@ public class Session extends SessionWithState implements TransactionStore.Rollba
         if (!locks.isEmpty() || needCommit) {
             database.commit(this);
         }
+        idsToRelease = null;
         cleanTempTables(false);
         if (autoCommitAtTransactionEnd) {
             autoCommit = true;