make append mode of MVMap more transparent

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

@@ -779,6 +779,11 @@ public class MVMap<K, V> extends AbstractMap<K, V>
     }
 
     public final RootReference getRoot() {
+        RootReference rootReference = getRootInternal();
+        return singleWriter ? flushAppendBuffer(rootReference) : rootReference;
+    }
+
+    private RootReference getRootInternal() {
         return root.get();
     }
 
@@ -1112,7 +1117,6 @@ public class MVMap<K, V> extends AbstractMap<K, V>
                 }
                 return rootReference;
             }
-            rootReference = flushAppendBuffer(rootReference);
             RootReference updatedRootReference = new RootReference(rootReference, writeVersion, ++attempt);
             if(root.compareAndSet(rootReference, updatedRootReference)) {
                 removeUnusedOldVersions(updatedRootReference);
@@ -1173,41 +1177,22 @@ public class MVMap<K, V> extends AbstractMap<K, V>
     /**
      * If map was used in append mode, this method will ensure that append buffer
      * is flushed - emptied with all entries inserted into map as a new leaf.
+     * @param rootReference current RootReference
      * @return potentially updated RootReference
      */
-    public RootReference flushAppendBuffer() {
-        return flushAppendBuffer(null);
-    }
-
     private RootReference flushAppendBuffer(RootReference rootReference) {
         int attempt = 0;
-        while(true) {
-            if (rootReference == null) {
-                rootReference = getRoot();
-            }
-            int keyCount = rootReference.getAppendCounter();
-            if (keyCount == 0) {
-                break;
-            }
+        int keyCount;
+        while((keyCount = rootReference.getAppendCounter()) > 0) {
             Page page = Page.create(this,
                     Arrays.copyOf(keysBuffer, keyCount),
                     Arrays.copyOf(valuesBuffer, keyCount),
                     null, keyCount, 0);
-            rootReference = appendLeafPage(rootReference, page, ++attempt);
-            if (rootReference != null) {
-                break;
-            }
-        }
-        assert rootReference.getAppendCounter() == 0;
-        return rootReference;
-    }
-
-    private RootReference appendLeafPage(RootReference rootReference, Page split, int attempt) {
             CursorPos pos = rootReference.root.getAppendCursorPos(null);
-        assert split.map == this;
+            assert page.map == this;
             assert pos != null;
-        assert split.getKeyCount() > 0;
-        Object key = split.getKey(0);
+            assert page.getKeyCount() > 0;
+            Object key = page.getKey(0);
             assert pos.index < 0 : pos.index;
             int index = -pos.index - 1;
             assert index == pos.page.getKeyCount() : index + " != " + pos.page.getKeyCount();
@@ -1218,13 +1203,13 @@ public class MVMap<K, V> extends AbstractMap<K, V>
             while (true) {
                 if (pos == null) {
                     if (p.getKeyCount() == 0) {
-                    p = split;
+                        p = page;
                     } else {
                         Object keys[] = new Object[] { key };
                         Page.PageReference children[] = new Page.PageReference[] {
                                                             new Page.PageReference(p),
-                                                        new Page.PageReference(split)};
-                    p = Page.create(this, keys, null, children, p.getTotalCount() + split.getTotalCount(), 0);
+                                                            new Page.PageReference(page)};
+                        p = Page.create(this, keys, null, children, p.getTotalCount() + page.getTotalCount(), 0);
                     }
                     break;
                 }
@@ -1233,17 +1218,16 @@ public class MVMap<K, V> extends AbstractMap<K, V>
                 index = pos.index;
                 pos = pos.parent;
                 p = p.copy();
-            p.setChild(index, split);
+                p.setChild(index, page);
                 p.insertNode(index, key, c);
-            int keyCount;
                 if ((keyCount = p.getKeyCount()) <= store.getKeysPerPage() &&
                         (p.getMemory() < store.getMaxPageSize() || keyCount <= (p.isLeaf() ? 1 : 2))) {
                     break;
                 }
                 int at = keyCount - 2;
                 key = p.getKey(at);
-            split = p.split(at);
-            unsavedMemory += p.getMemory() + split.getMemory();
+                page = p.split(at);
+                unsavedMemory += p.getMemory() + page.getMemory();
             }
             unsavedMemory += p.getMemory();
             while (pos != null) {
@@ -1263,9 +1247,12 @@ public class MVMap<K, V> extends AbstractMap<K, V>
                 if (store.getFileStore() != null) {
                     store.registerUnsavedPage(unsavedMemory);
                 }
+                assert updatedRootReference.getAppendCounter() == 0;
                 return updatedRootReference;
             }
-        return null;
+            rootReference = getRootInternal();
+        }
+        return rootReference;
     }
 
     /**
@@ -1280,7 +1267,7 @@ public class MVMap<K, V> extends AbstractMap<K, V>
         int attempt = 0;
         boolean success = false;
         while(!success) {
-            RootReference rootReference = getRoot();
+            RootReference rootReference = getRootInternal();
             int appendCounter = rootReference.getAppendCounter();
             if (appendCounter >= keysPerPage) {
                 rootReference = flushAppendBuffer(rootReference);

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

@@ -83,7 +83,6 @@ public final class MVSecondaryIndex extends BaseIndex implements MVIndex {
             ValueArray key = convertToKey(row);
             map.append(key, ValueNull.INSTANCE);
         }
-        map.flushAppendBuffer();
     }
 
     private static final class Source {

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

@@ -88,7 +88,7 @@ public class TransactionMap<K, V> {
             for (int i = opentransactions.nextSetBit(0); i >= 0; i = opentransactions.nextSetBit(i+1)) {
                 MVMap<Long, Object[]> undoLog = store.undoLogs[i];
                 if (undoLog != null) {
-                    MVMap.RootReference rootReference = undoLog.flushAppendBuffer();
+                    MVMap.RootReference rootReference = undoLog.getRoot();
                     undoLogRootReferences[i] = rootReference;
                     undoLogSize += rootReference.root.getTotalCount() + rootReference.getAppendCounter();
                 }

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

@@ -439,9 +439,7 @@ public class TransactionStore {
                     store.renameMap(undoLog, getUndoLogName(true, transactionId));
                 }
                 try {
-                    MVMap.RootReference rootReference = undoLog.flushAppendBuffer();
-                    Page rootPage = rootReference.root;
-                    Cursor<Long, Object[]> cursor = new Cursor<>(rootPage, null);
+                    Cursor<Long, Object[]> cursor = undoLog.cursor(null);
                     while (cursor.hasNext()) {
                         Long undoKey = cursor.next();
                         Object[] op = cursor.getValue();
@@ -592,7 +590,6 @@ public class TransactionStore {
     void rollbackTo(Transaction t, long maxLogId, long toLogId) {
         int transactionId = t.getId();
         MVMap<Long, Object[]> undoLog = undoLogs[transactionId];
-        undoLog.flushAppendBuffer();
         RollbackDecisionMaker decisionMaker = new RollbackDecisionMaker(this, transactionId, toLogId, t.listener);
         for (long logId = maxLogId - 1; logId >= toLogId; logId--) {
             Long undoKey = getOperationId(transactionId, logId);
@@ -614,7 +611,6 @@ public class TransactionStore {
             final long toLogId) {
 
         final MVMap<Long, Object[]> undoLog = undoLogs[t.getId()];
-        undoLog.flushAppendBuffer();
         return new Iterator<Change>() {
 
             private long logId = maxLogId - 1;