atognolag commented on code in PR #38406:
URL: https://github.com/apache/beam/pull/38406#discussion_r3203048872


##########
sdks/java/io/iceberg/src/main/java/org/apache/beam/sdk/io/iceberg/IcebergRowSorter.java:
##########
@@ -0,0 +1,234 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.beam.sdk.io.iceberg;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.Serializable;
+import java.nio.ByteBuffer;
+import java.nio.charset.StandardCharsets;
+import java.time.Instant;
+import java.util.Date;
+import java.util.Iterator;
+import org.apache.beam.sdk.coders.RowCoder;
+import org.apache.beam.sdk.extensions.sorter.BufferedExternalSorter;
+import org.apache.beam.sdk.values.KV;
+import org.apache.beam.sdk.values.Row;
+import org.apache.iceberg.NullOrder;
+import org.apache.iceberg.Schema;
+import org.apache.iceberg.SortDirection;
+import org.apache.iceberg.SortField;
+import org.apache.iceberg.SortOrder;
+import org.checkerframework.checker.nullness.qual.Nullable;
+import org.joda.time.ReadableInstant;
+
+/**
+ * A utility class to sort Beam {@link Row}s based on an Iceberg {@link 
SortOrder}. Leverages {@link
+ * BufferedExternalSorter} to spill to local disk when elements exceed memory 
limit.
+ */
+class IcebergRowSorter implements Serializable {
+
+  public static Iterable<Row> sortRows(
+      Iterable<Row> rows,
+      SortOrder sortOrder,
+      Schema icebergSchema,
+      org.apache.beam.sdk.schemas.Schema beamSchema) {
+
+    if (sortOrder == null || !sortOrder.isSorted()) {
+      return rows;
+    }
+
+    BufferedExternalSorter.Options sorterOptions = 
BufferedExternalSorter.options();
+    BufferedExternalSorter sorter = 
BufferedExternalSorter.create(sorterOptions);
+    RowCoder rowCoder = RowCoder.of(beamSchema);
+
+    try {
+      for (Row row : rows) {
+        byte[] keyBytes = encodeSortKey(row, sortOrder, icebergSchema, 
beamSchema);
+        ByteArrayOutputStream baos = new ByteArrayOutputStream();
+        rowCoder.encode(row, baos);
+        byte[] valBytes = baos.toByteArray();
+        sorter.add(KV.of(keyBytes, valBytes));
+      }
+
+      Iterable<KV<byte[], byte[]>> sortedKVs = sorter.sort();
+      return new Iterable<Row>() {
+        @Override
+        public Iterator<Row> iterator() {
+          final Iterator<KV<byte[], byte[]>> it = sortedKVs.iterator();
+          return new Iterator<Row>() {
+            @Override
+            public boolean hasNext() {
+              return it.hasNext();
+            }
+
+            @Override
+            public Row next() {
+              KV<byte[], byte[]> next = it.next();
+              try {
+                ByteArrayInputStream bais = new 
ByteArrayInputStream(next.getValue());
+                return rowCoder.decode(bais);
+              } catch (IOException e) {
+                throw new RuntimeException("Failed to decode Row during 
sorting", e);
+              }
+            }
+          };
+        }
+      };
+
+    } catch (IOException e) {
+      throw new RuntimeException("Failed to sort rows with external sorter", 
e);
+    }
+  }
+
+  @SuppressWarnings("nullness")
+  public static byte[] encodeSortKey(
+      Row row,
+      SortOrder sortOrder,
+      Schema icebergSchema,
+      org.apache.beam.sdk.schemas.Schema beamSchema)
+      throws IOException {
+
+    ByteArrayOutputStream baos = new ByteArrayOutputStream();
+
+    for (SortField field : sortOrder.fields()) {
+      String colName = icebergSchema.findColumnName(field.sourceId());
+      Object val = row.getValue(colName);
+
+      if (!field.transform().isIdentity()) {
+        Object icebergVal =
+            IcebergUtils.beamRowToIcebergRecord(icebergSchema, 
row).getField(colName);
+        if (icebergVal != null) {
+          val = field.transform().apply(icebergVal);
+        } else {
+          val = null;
+        }
+      }
+
+      boolean isNull = (val == null);
+      boolean isDesc = (field.direction() == SortDirection.DESC);
+      boolean nullsFirst = (field.nullOrder() == NullOrder.NULLS_FIRST);
+
+      // Determine correct header prefix to fulfill the NullOrder contracts
+      byte prefixByte;
+      if (isNull) {
+        if (isDesc) {
+          // Descending: High byte keys sort first.
+          // If Nulls First -> Null gets highest byte (0xFF)
+          // If Nulls Last -> Null gets lowest byte (0x00)
+          prefixByte = nullsFirst ? (byte) 0xFF : (byte) 0x00;
+        } else {
+          // Ascending: Low byte keys sort first.
+          // If Nulls First -> Null gets lowest byte (0x00)
+          // If Nulls Last -> Null gets highest byte (0xFF)
+          prefixByte = nullsFirst ? (byte) 0x00 : (byte) 0xFF;
+        }
+      } else {
+        if (isDesc) {
+          // If non-null and Descending, use a neutral value that sits 
opposite to the null byte
+          prefixByte = nullsFirst ? (byte) 0xFE : (byte) 0x01;
+        } else {
+          prefixByte = nullsFirst ? (byte) 0x01 : (byte) 0x00;
+        }
+      }
+
+      baos.write(prefixByte);
+
+      if (!isNull) {
+        byte[] valBytes = encodeValue(val);
+        // Bitwise invert non-null bytes to sort descending lexicographically
+        if (isDesc) {
+          for (int i = 0; i < valBytes.length; i++) {
+            valBytes[i] = (byte) ~valBytes[i];
+          }
+        }
+        baos.write(valBytes);
+      }
+    }
+
+    return baos.toByteArray();
+  }
+
+  @SuppressWarnings("JavaUtilDate")
+  private static byte[] encodeValue(@Nullable Object val) throws IOException {
+    if (val == null) {
+      return new byte[0];
+    }
+    if (val instanceof String) {
+      return encodeString((String) val);
+    } else if (val instanceof Integer) {
+      int v = (Integer) val;
+      return ByteBuffer.allocate(4).putInt(v ^ Integer.MIN_VALUE).array();
+    } else if (val instanceof Long) {
+      long v = (Long) val;
+      return ByteBuffer.allocate(8).putLong(v ^ Long.MIN_VALUE).array();
+    } else if (val instanceof Float) {
+      int bits = Float.floatToIntBits((Float) val);
+      bits = (bits >= 0) ? (bits ^ Integer.MIN_VALUE) : ~bits;
+      return ByteBuffer.allocate(4).putInt(bits).array();
+    } else if (val instanceof Double) {
+      long bits = Double.doubleToLongBits((Double) val);
+      bits = (bits >= 0) ? (bits ^ Long.MIN_VALUE) : ~bits;
+      return ByteBuffer.allocate(8).putLong(bits).array();

Review Comment:
   The IcebergRowSorter.java now uses bit manipulation directly into the 
destination ByteArrayOutputStream, supporting inline byte inversion without 
allocating any heap objects.



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