Fixed a deadlock related to very large temporary result sets.

h2/src/main/org/h2/result/ResultTempTable.java

@@ -155,20 +155,18 @@ public class ResultTempTable implements ResultExternal {
             table.truncate(session);
             Database database = session.getDatabase();
             synchronized (database) {
+                // This session may not lock the sys table (except if it already has locked it)
+                // because it must be committed immediately,
+                // otherwise other threads can not access the sys table.
+                // If the table is not removed now, it will be when the database
+                // is opened the next time.
+                // (the table is truncated, so this is just one record)
                 if (!database.isSysTableLocked()) {
                     Session sysSession = database.getSystemSession();
-                    // This session may not lock the sys table (except if it already has locked it)
-                    // because it must be committed immediately,
-                    // otherwise other threads can not access the sys table.
-                    // If the table is not removed now, it will be when the database
-                    // is opened the next time.
-                    // (the table is truncated, so this is just one record)
-                    synchronized (sysSession) {
-                        index.removeChildrenAndResources(sysSession);
-                        table.removeChildrenAndResources(sysSession);
-                        // the transaction must be committed immediately
-                        sysSession.commit(false);
-                    }
+                    index.removeChildrenAndResources(sysSession);
+                    table.removeChildrenAndResources(sysSession);
+                    // the transaction must be committed immediately
+                    sysSession.commit(false);
                 }
             }
         } finally {