Lazy-allocate the Row list to speedup drop or create use cases

h2database · Mar 14, 2023 · 8a17940 · 8a17940
1 parent 1d21f2e
commit 8a17940
Showing 1 changed file with 18 additions and 4 deletions.
diff --git a/h2/src/main/org/h2/mvstore/db/MVTable.java b/h2/src/main/org/h2/mvstore/db/MVTable.java
@@ -7,7 +7,9 @@
 
 import java.util.ArrayDeque;
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.HashSet;
+import java.util.List;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -419,11 +421,14 @@ private void rebuildIndexBlockMerge(SessionLocal session, MVIndex<?,?> index) {
         Store store = session.getDatabase().getStore();
 
         int bufferSize = database.getMaxMemoryRows() / 2;
-        ArrayList<Row> buffer = new ArrayList<>(bufferSize);
+        List<Row> buffer = null;
         String n = getName() + ':' + index.getName();
         ArrayList<String> bufferNames = Utils.newSmallArrayList();
         while (cursor.next()) {
             Row row = cursor.get();
+            if (buffer == null) {
+                buffer = new ArrayList<>(bufferSize);
+            }
             buffer.add(row);
             database.setProgress(DatabaseEventListener.STATE_CREATE_INDEX, n, i++, total);
             if (buffer.size() >= bufferSize) {
@@ -435,6 +440,9 @@ private void rebuildIndexBlockMerge(SessionLocal session, MVIndex<?,?> index) {
             }
             remaining--;
         }
+        if (buffer == null) {
+            buffer = Collections.emptyList();
+        }
         sortRows(buffer, index);
         if (!bufferNames.isEmpty()) {
             String mapName = store.nextTemporaryMapName();
@@ -457,17 +465,23 @@ private void rebuildIndexBuffered(SessionLocal session, Index index) {
         Cursor cursor = scan.find(session, null, null);
         long i = 0;
         int bufferSize = (int) Math.min(total, database.getMaxMemoryRows());
-        ArrayList<Row> buffer = new ArrayList<>(bufferSize);
+        List<Row> buffer = null;
         String n = getName() + ':' + index.getName();
         while (cursor.next()) {
             Row row = cursor.get();
+            if (buffer == null) {
+                buffer = new ArrayList<>(bufferSize);
+            }
             buffer.add(row);
             database.setProgress(DatabaseEventListener.STATE_CREATE_INDEX, n, i++, total);
             if (buffer.size() >= bufferSize) {
                 addRowsToIndex(session, buffer, index);
             }
             remaining--;
         }
+        if (buffer == null) {
+            buffer = Collections.emptyList();
+        }
         addRowsToIndex(session, buffer, index);
         if (remaining != 0) {
             throw DbException.getInternalError("rowcount remaining=" + remaining + ' ' + getName());
@@ -703,7 +717,7 @@ public int getMainIndexColumn() {
      * @param index
      *            the index to append to
      */
-    private static void addRowsToIndex(SessionLocal session, ArrayList<Row> list, Index index) {
+    private static void addRowsToIndex(SessionLocal session, List<Row> list, Index index) {
         sortRows(list, index);
         for (Row row : list) {
             index.add(session, row);
@@ -763,7 +777,7 @@ private static String lockTypeToString(int lockType) {
      * @param index
      *            the index to sort for
      */
-    private static void sortRows(ArrayList<? extends SearchRow> list, final Index index) {
+    private static void sortRows(List<? extends SearchRow> list, final Index index) {
         list.sort(index::compareRows);
     }