xushiyan commented on code in PR #18040:
URL: https://github.com/apache/hudi/pull/18040#discussion_r2748979018


##########
hudi-flink-datasource/hudi-flink/src/main/java/org/apache/hudi/source/reader/HoodieRecordEmitter.java:
##########
@@ -18,19 +18,75 @@
 
 package org.apache.hudi.source.reader;
 
+import org.apache.flink.api.common.eventtime.Watermark;
 import org.apache.flink.api.connector.source.SourceOutput;
 import org.apache.flink.connector.base.source.reader.RecordEmitter;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import org.apache.hudi.common.fs.FSUtils;
 import org.apache.hudi.source.split.HoodieSourceSplit;
 
 /**
  * Default Hoodie record emitter.
- * @param <T>
+ *
+ * <p>This emitter handles watermark emission based on split information.
+ *
+ * @param <T> The type of records to emit
  */
 public class HoodieRecordEmitter<T> implements 
RecordEmitter<HoodieRecordWithPosition<T>, T, HoodieSourceSplit> {
+  private static final Logger LOG = 
LoggerFactory.getLogger(HoodieRecordEmitter.class);
+  private HoodieSourceSplit lastSplit = null;
+  private long watermark = Long.MIN_VALUE;
 
   @Override
   public void emitRecord(HoodieRecordWithPosition<T> record, SourceOutput<T> 
output, HoodieSourceSplit split) throws Exception {
+    if (lastSplit == null || !split.splitId().equals(lastSplit.splitId())) {
+      long newWatermark = extractWatermark(split);
+      if (newWatermark < watermark) {
+        LOG.warn(
+            "Received a new split with lower watermark. Previous watermark = 
{}, current watermark = {}, previous split = {}, current split = {}",
+            watermark,
+            newWatermark,
+            lastSplit,
+            split);
+      } else {
+        watermark = newWatermark;
+        output.emitWatermark(new Watermark(watermark));
+        LOG.debug("Watermark = {} emitted based on split = {}", watermark, 
split);
+      }
+
+      lastSplit = split;
+    }
+
     output.collect(record.record());
     split.updatePosition(record.fileOffset(), record.recordOffset());

Review Comment:
   ok saw the comment:
   
   > emit the watermark of previous finished split
   
   so do we have to couple the record processing with split level emission? is 
there a method hook for split processing like `onSplitFinish()` where emitting 
watermark would be more appropriate?



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