step toward atomic transaction commit

h2/src/main/org/h2/mvstore/MVMap.java

@@ -379,9 +379,19 @@ public class MVMap<K, V> extends AbstractMap<K, V>
      * @return the value, or null if not found
      */
     @Override
+    public final V get(Object key) {
+        return get(getRootPage(), key);
+    }
+
+    /**
+     * Get the value for the given key from a snapshot, or null if not found.
+     *
+     * @param p the root of a snapshot
+     * @param key the key
+     * @return the value, or null if not found
+     */
     @SuppressWarnings("unchecked")
-    public V get(Object key) {
-        Page p = getRootPage();
+    public V get(Page p, Object key) {
         return (V) Page.get(p, key);
     }
 

h2/src/main/org/h2/mvstore/Page.java

@@ -183,7 +183,7 @@ public abstract class Page implements Cloneable
      * @param p the root page
      * @return the value, or null if not found
      */
-    public static Object get(Page p, Object key) {
+    static Object get(Page p, Object key) {
         while (true) {
             int index = p.binarySearch(key);
             if (p.isLeaf()) {

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

@@ -210,7 +210,7 @@ public final class MVSecondaryIndex extends BaseIndex implements MVIndex {
         }
         if (unique != null) {
             // This code expects that mayHaveDuplicates(row) == false
-            Iterator<Value> it = map.keyIterator(unique, true);
+            Iterator<Value> it = map.keyIterator(unique, null, true);
             while (it.hasNext()) {
                 ValueArray k = (ValueArray) it.next();
                 if (compareRows(row, convertToSearchRow(k)) != 0) {

h2/src/main/org/h2/mvstore/rtree/MVRTreeMap.java

@@ -48,12 +48,6 @@ public final class MVRTreeMap<V> extends MVMap<SpatialKey, V> {
         return new MVRTreeMap<>(this);
     }
 
-    @Override
-    public V get(Object key) {
-        V result = get(getRootPage(), key);
-        return result;
-    }
-
     /**
      * Iterate over all keys that have an intersection with the given rectangle.
      *
@@ -102,6 +96,7 @@ public final class MVRTreeMap<V> extends MVMap<SpatialKey, V> {
      * @return the value, or null if not found
      */
     @SuppressWarnings("unchecked")
+    @Override
     public V get(Page p, Object key) {
         int keyCount = p.getKeyCount();
         if (!p.isLeaf()) {

h2/src/main/org/h2/mvstore/tx/TransactionStore.java

@@ -374,7 +374,7 @@ public class TransactionStore {
      * @param key the key
      * @param oldValue the old value
      */
-    void log(Transaction t, long logId, int mapId,
+    long log(Transaction t, long logId, int mapId,
             Object key, Object oldValue) {
         Long undoKey = getOperationId(t.getId(), logId);
         Object[] log = { mapId, key, oldValue };
@@ -393,6 +393,7 @@ public class TransactionStore {
         } finally {
             rwLock.writeLock().unlock();
         }
+        return undoKey;
     }
 
     /**

h2/src/main/org/h2/mvstore/tx/VersionedValue.java

@@ -31,6 +31,10 @@ public class VersionedValue {
         this.value = value;
     }
 
+    public long getOperationId() {
+        return operationId;
+    }
+
     @Override
     public String toString() {
         return value + (operationId == 0 ? "" : (