scwhittle commented on code in PR #32456:
URL: https://github.com/apache/beam/pull/32456#discussion_r1771402593


##########
sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/ReadFromKafkaDoFn.java:
##########
@@ -460,7 +460,28 @@ public ProcessContinuation processElement(
           }
           return ProcessContinuation.resume();
         }
+        long skippedRecords = 0L;
+        final Stopwatch sw = Stopwatch.createStarted();
         for (ConsumerRecord<byte[], byte[]> rawRecord : rawRecords) {
+          // If the Kafka consumer returns a record with an offset that is 
already processed
+          // the record can be safely skipped. This is needed because there is 
a possibility
+          // that the seek() above fails to move the offset to the desired 
position. In which
+          // case poll() would return records that are already cnsumed.
+          if (rawRecord.offset() < startOffset) {
+            // If the start offset is not reached even after skipping the 
records for 10 seconds
+            // then the processing is stopped with a backoff to give the Kakfa 
server some time
+            // catch up.
+            if (sw.elapsed().getSeconds() > 10L) {
+              LOG.error(
+                  "The expected offset was not reached even after skipping 
consumed records for 10 seconds,"
+                      + " the processing of this bundle will be attempted at a 
later time.");
+              return ProcessContinuation.resume()
+                  
.withResumeDelay(org.joda.time.Duration.standardSeconds(10L));
+            } else {
+              skippedRecords++;
+              continue;
+            }
+          }
           if (!tracker.tryClaim(rawRecord.offset())) {

Review Comment:
   You can set skippedRecords to 0 to prevent that, see the code snippet above.
   I would like to just log we skipped X records once, not per record we skip 
or per-batch of records we skip (and not per record we don't skip either :) )



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