MVStore: in some cases, CLOB/BLOB data blocks were removed incorrectly when opening a database.

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

@@ -123,6 +123,11 @@ public class LobStorageMap implements LobStorageInterface {
             }
             dataMap.remove(last);
         }
+        // don't re-use block ids, except at the very end
+        Long last = dataMap.lastKey();
+        if (last != null) {
+            streamStore.setNextKey(last + 1);
+        }
     }
 
     @Override

h2/src/test/org/h2/test/store/TestMVTableEngine.java

@@ -51,6 +51,7 @@ public class TestMVTableEngine extends TestBase {
 
     @Override
     public void test() throws Exception {
+        testLobReuse();
         testShutdownDuringLobCreation();
         testLobCreationThenShutdown();
         testManyTransactions();
@@ -86,6 +87,30 @@ public class TestMVTableEngine extends TestBase {
         testLocking();
         testSimple();
     }
+    
+    private void testLobReuse() throws Exception {
+        deleteDb("testLobReuse");
+        Connection conn = getConnection("testLobReuse");
+        Statement stat = conn.createStatement();
+        stat.execute("create table test(id identity primary key, lob clob)");
+        conn.close();
+        byte[] buffer = new byte[8192];
+        for (int i = 0; i < 20; i++) {
+            conn = getConnection("testLobReuse");
+            stat = conn.createStatement();
+            stat.execute("insert into test(lob) select space(1025) from system_range(1, 10)");
+            stat.execute("delete from test where random() > 0.5");
+            ResultSet rs = conn.createStatement().executeQuery(
+                    "select lob from test");
+            while (rs.next()) {
+                InputStream is = rs.getBinaryStream(1);
+                while (is.read(buffer) != -1) {
+                    // ignore
+                }
+            }
+            conn.close();
+        }
+    }
 
     private void testShutdownDuringLobCreation() throws Exception {
         deleteDb("testShutdownDuringLobCreation");