Preserve original page objects when region remains unchanged

Avoid creating new objects when region is same as original page Cherry-pick of trinodb/trino@122f513 (trinodb/trino#17385) Co-authored-by: Karol Sobczak <[email protected]>
prestodb · Dec 19, 2023 · 1e6dc1d · 1e6dc1d
1 parent 2e140a6
commit 1e6dc1d
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Showing 2 changed files with 15 additions and 2 deletions.
diff --git a/presto-common/src/main/java/com/facebook/presto/common/Page.java b/presto-common/src/main/java/com/facebook/presto/common/Page.java
@@ -164,12 +164,19 @@ public Page getSingleValuePage(int position)
         return wrapBlocksWithoutCopy(1, singleValueBlocks);
     }
 
+    // getRegion() is used to get a sub-page or region of a page based on the given positionOffset and length
     public Page getRegion(int positionOffset, int length)
     {
         if (positionOffset < 0 || length < 0 || positionOffset + length > positionCount) {
             throw new IndexOutOfBoundsException(format("Invalid position %s and length %s in page with %s positions", positionOffset, length, positionCount));
         }
 
+        // Avoid creating new objects when region is same as original page
+        if (positionOffset == 0 && length == positionCount) {
+            return this;
+        }
+
+        // Create a new page view with the specified region
         int channelCount = getChannelCount();
         Block[] slicedBlocks = new Block[channelCount];
         for (int i = 0; i < channelCount; i++) {

diff --git a/presto-common/src/test/java/com/facebook/presto/common/TestPage.java b/presto-common/src/test/java/com/facebook/presto/common/TestPage.java
@@ -33,21 +33,27 @@
 import static com.google.common.base.Verify.verify;
 import static org.testng.Assert.assertEquals;
 import static org.testng.Assert.assertNotEquals;
+import static org.testng.Assert.assertSame;
 import static org.testng.Assert.assertTrue;
 
 public class TestPage
 {
     @Test
     public void testGetRegion()
     {
-        assertEquals(new Page(10).getRegion(5, 5).getPositionCount(), 5);
+        Page page = new Page(10);
+        Page region = page.getRegion(0, 10);
+        assertEquals(page.getRegion(5, 5).getPositionCount(), 5);
+        assertEquals(region.getPositionCount(), 10);
+        assertSame(page, region);
     }
 
     @Test
     public void testGetEmptyRegion()
     {
+        Page page = new Page(10);
         assertEquals(new Page(0).getRegion(0, 0).getPositionCount(), 0);
-        assertEquals(new Page(10).getRegion(5, 0).getPositionCount(), 0);
+        assertEquals(page.getRegion(5, 0).getPositionCount(), 0);
     }
 
     @Test(expectedExceptions = IndexOutOfBoundsException.class, expectedExceptionsMessageRegExp = "Invalid position 1 and length 1 in page with 0 positions")