Copilot commented on code in PR #54572:
URL: https://github.com/apache/spark/pull/54572#discussion_r2872593232
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core/src/test/scala/org/apache/spark/util/SizeEstimatorSuite.scala:
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@@ -243,4 +247,76 @@ class SizeEstimatorSuite
assertResult(2015)(SizeEstimator.estimate(new DummyClass8))
assertResult(20206)(SizeEstimator.estimate(Array.fill(10)(new
DummyClass8)))
}
+
+ // Tests for JEP 450/519: Compact Object Headers
+ // With compact object headers, the object header is 8 bytes (vs. 12 with
compressed oops,
+ // or 16 without) because the class pointer is encoded inside the mark word.
+ // Object references are still 4 bytes (like compressed oops).
+
+ test("64-bit arch with compact object headers: simple classes") {
+ reinitializeSizeEstimator("amd64", "true", "true")
+ // objectSize = 8 (compact header), pointerSize = 4
+ // DummyClass1: 8-byte header, no fields => 8 bytes
+ assertResult(8)(SizeEstimator.estimate(new DummyClass1))
+ // DummyClass2: 8-byte header + Int(4) => 12, aligned to 16
+ assertResult(16)(SizeEstimator.estimate(new DummyClass2))
+ // DummyClass3: 8-byte header + Int(4) + Double(8) => 20, aligned to 24
+ assertResult(24)(SizeEstimator.estimate(new DummyClass3))
+ // DummyClass4: 8-byte header + Int(4) + pointer(4) => 16, aligned to 16
+ assertResult(16)(SizeEstimator.estimate(new DummyClass4(null)))
+ // DummyClass4 with DummyClass3: 16 + 24 = 40
+ assertResult(40)(SizeEstimator.estimate(new DummyClass4(new DummyClass3)))
+ }
+
+ test("64-bit arch with compact object headers: primitive wrapper objects") {
+ reinitializeSizeEstimator("amd64", "true", "true")
+ // Boolean/Byte/Char/Short/Int/Float wrappers: 8-byte header + primitive
up to 4 bytes => 16
+ assertResult(16)(SizeEstimator.estimate(java.lang.Boolean.TRUE))
+ assertResult(16)(SizeEstimator.estimate(java.lang.Byte.valueOf("1")))
+ assertResult(16)(SizeEstimator.estimate(java.lang.Character.valueOf('1')))
+ assertResult(16)(SizeEstimator.estimate(java.lang.Short.valueOf("1")))
+ assertResult(16)(SizeEstimator.estimate(java.lang.Integer.valueOf(1)))
+ assertResult(16)(SizeEstimator.estimate(java.lang.Float.valueOf(1.0f)))
+ // Long/Double wrappers: 8-byte header + 8-byte primitive => 16
+ assertResult(16)(SizeEstimator.estimate(java.lang.Long.valueOf(1)))
+ assertResult(16)(SizeEstimator.estimate(java.lang.Double.valueOf(1.0)))
+ }
+
+ test("64-bit arch with compact object headers: primitive arrays") {
+ reinitializeSizeEstimator("amd64", "true", "true")
+ // Array header = objectSize(8) + length Int(4) = 12, aligned to 16
+ // Array[Byte](10): 16 + alignSize(10*1=10) = 16 + 16 = 32
+ assertResult(32)(SizeEstimator.estimate(new Array[Byte](10)))
+ // Array[Char](10): 16 + alignSize(10*2=20) = 16 + 24 = 40
+ assertResult(40)(SizeEstimator.estimate(new Array[Char](10)))
+ // Array[Int](10): 16 + alignSize(10*4=40) = 16 + 40 = 56
+ assertResult(56)(SizeEstimator.estimate(new Array[Int](10)))
+ // Array[Long](10): 16 + alignSize(10*8=80) = 16 + 80 = 96
+ assertResult(96)(SizeEstimator.estimate(new Array[Long](10)))
+ }
+
+ test("64-bit arch with compact object headers: strings") {
+ reinitializeSizeEstimator("amd64", "true", "true")
+ // DummyString has: pointer(arr,4) + Int(hashCode,4) + Int(hash32,4) = 12
fields
+ // objectSize=8, fields=12 => shellSize=20, aligned to 24
Review Comment:
The comment says "= 12 fields" but the calculation is in bytes (4 + 4 + 4 =
12 bytes). Consider correcting the wording to avoid confusion when maintaining
these size derivations.
```suggestion
// DummyString has: pointer(arr,4) + Int(hashCode,4) + Int(hash32,4) =
12 bytes
// objectSize=8, fieldBytes=12 => shellSize=20, aligned to 24
```
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