New connection setting "REUSE_SPACE".

h2/src/docsrc/html/changelog.html

@@ -17,7 +17,11 @@ Change Log
 <h1>Change Log</h1>
 
 <h2>Next Version (unreleased)</h2>
-<ul><li>Issue 587: MVStore: concurrent compaction and store operations could result in an IllegalStateException.
+<ul><li>New connection setting "REUSE_SPACE" (default: true). If disabled,
+    all changes are appended to the database file, and existing content is never overwritten.
+    This allows to rollback to a previous state of the database by truncating
+    the database file.
+</li><li>Issue 587: MVStore: concurrent compaction and store operations could result in an IllegalStateException.
 </li><li>Issue 594: Profiler.copyInThread does not work properly.
 </li><li>Script tool: Now, SCRIPT ... TO is always used (for higher speed and lower disk space usage).
 </li><li>Script tool: Fix parsing of BLOCKSIZE parameter, original patch by Ken Jorissen.

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

@@ -282,6 +282,13 @@ public class DbSettings extends SettingsBase {
      */
     public final int reconnectCheckDelay = get("RECONNECT_CHECK_DELAY", 200);
     
+    /**
+     * Database setting <code>REUSE_SPACE</code> (default: true).<br />
+     * If disabled, all changes are appended to the database file, and existing
+     * content is never overwritten. This setting has no effect if the database is already open.
+     */
+    public final boolean reuseSpace = get("REUSE_SPACE", true);
+
     /**
      * Database setting <code>ROWID</code> (default: true).<br />
      * If set, each table has a pseudo-column _ROWID_.

h2/src/main/org/h2/mvstore/db/MVTableEngine.java

@@ -160,6 +160,9 @@ public class MVTableEngine implements TableEngine {
 
         public Store(Database db, MVStore.Builder builder) {
             this.store = builder.open();
+            if (!db.getSettings().reuseSpace) {
+                store.setReuseSpace(false);
+            }
             this.transactionStore = new TransactionStore(
                     store,
                     new ValueDataType(null, db, null));

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

@@ -9,6 +9,7 @@ import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.math.BigDecimal;
+import java.nio.channels.FileChannel;
 import java.sql.Connection;
 import java.sql.DriverManager;
 import java.sql.PreparedStatement;
@@ -48,6 +49,7 @@ public class TestMVTableEngine extends TestBase {
 
     @Override
     public void test() throws Exception {
+        testAppendOnly();
         testLowRetentionTime();
         testOldAndNew();
         testTemporaryTables();
@@ -80,6 +82,48 @@ public class TestMVTableEngine extends TestBase {
         testSimple();
     }
     
+    private void testAppendOnly() throws Exception {
+        deleteDb("testAppendOnly");
+        Connection conn = getConnection(
+                "testAppendOnly");
+        Statement stat = conn.createStatement();
+        stat.execute("set retention_time 0");
+        for (int i = 0; i < 10; i++) {
+            stat.execute("create table dummy" + i +
+                    " as select x, space(100) from system_range(1, 1000)");
+            stat.execute("checkpoint");
+        }
+        stat.execute("create table test as select x from system_range(1, 1000)");
+        conn.close();
+        String fileName = getBaseDir() + "/testAppendOnly" + Constants.SUFFIX_MV_FILE;
+        long fileSize = FileUtils.size(fileName);
+        
+        conn = getConnection(
+                "testAppendOnly;reuse_space=false");
+        stat = conn.createStatement();
+        stat.execute("set retention_time 0");
+        for (int i = 0; i < 10; i++) {
+            stat.execute("drop table dummy" + i);
+            stat.execute("checkpoint");
+        }
+        stat.execute("alter table test alter column x rename to y");
+        stat.execute("select y from test where 1 = 0");
+        stat.execute("create table test2 as select x from system_range(1, 1000)");
+        conn.close();
+        
+        FileChannel fc = FileUtils.open(fileName, "rw");
+        // undo all changes
+        fc.truncate(fileSize);
+        
+        conn = getConnection(
+                "testAppendOnly");
+        stat = conn.createStatement();
+        stat.execute("select * from dummy0 where 1 = 0");
+        stat.execute("select * from dummy9 where 1 = 0");
+        stat.execute("select x from test where 1 = 0");
+        conn.close();
+    }
+
     private void testLowRetentionTime() throws SQLException {
         deleteDb("testLowRetentionTime");
         Connection conn = getConnection(