Adds triggerring configuration to KafkaIO eos.

sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaExactlyOnceSink.java

@@ -51,9 +51,12 @@
 import org.apache.beam.sdk.transforms.PTransform;
 import org.apache.beam.sdk.transforms.ParDo;
 import org.apache.beam.sdk.transforms.SerializableFunction;
+import org.apache.beam.sdk.transforms.windowing.AfterFirst;
 import org.apache.beam.sdk.transforms.windowing.AfterPane;
+import org.apache.beam.sdk.transforms.windowing.AfterProcessingTime;
 import org.apache.beam.sdk.transforms.windowing.GlobalWindows;
 import org.apache.beam.sdk.transforms.windowing.Repeatedly;
+import org.apache.beam.sdk.transforms.windowing.Trigger;
 import org.apache.beam.sdk.transforms.windowing.Window;
 import org.apache.beam.sdk.util.Preconditions;
 import org.apache.beam.sdk.values.KV;
@@ -84,6 +87,7 @@
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.joda.time.DateTimeUtils;
 import org.joda.time.DateTimeZone;
+import org.joda.time.Duration;
 import org.joda.time.format.DateTimeFormat;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -159,7 +163,8 @@ static void ensureEOSSupport() {
   @Override
   public PCollection<Void> expand(PCollection<ProducerRecord<K, V>> input) {
     String topic = Preconditions.checkStateNotNull(spec.getTopic());
-
+    int numElements = spec.getEosTriggerNumElements();
+    Duration timeout = spec.getEosTriggerTimeout();
     int numShards = spec.getNumShards();
     if (numShards <= 0) {
       try (Consumer<?, ?> consumer = openConsumer(spec)) {
@@ -172,17 +177,34 @@ public PCollection<Void> expand(PCollection<ProducerRecord<K, V>> input) {
       }
     }
     checkState(numShards > 0, "Could not set number of shards");
-
+    Trigger.OnceTrigger trigger = null;
+    if (timeout != null) {
+      trigger =
+          AfterFirst.of(
+              AfterPane.elementCountAtLeast(numElements),
+              AfterProcessingTime.pastFirstElementInPane().plusDelayOf(timeout));
+    } else {
+      // fallback to default
+      trigger = AfterPane.elementCountAtLeast(numElements);
+    }
     return input
         .apply(
             Window.<ProducerRecord<K, V>>into(new GlobalWindows()) // Everything into global window.
-                .triggering(Repeatedly.forever(AfterPane.elementCountAtLeast(1)))
+                .triggering(Repeatedly.forever(trigger))
                 .discardingFiredPanes())
         .apply(
             String.format("Shuffle across %d shards", numShards),
             ParDo.of(new Reshard<>(numShards)))
         .apply("Persist sharding", GroupByKey.create())
         .apply("Assign sequential ids", ParDo.of(new Sequencer<>()))
+        // Reapply the windowing configuration as the continuation trigger doesn't maintain the
+        // desired batching.
+        .apply(
+            "Windowing",
+            Window.<KV<Integer, KV<Long, TimestampedValue<ProducerRecord<K, V>>>>>into(
+                    new GlobalWindows()) // Everything into global window.
+                .triggering(Repeatedly.forever(trigger))
+                .discardingFiredPanes())
         .apply("Persist ids", GroupByKey.create())
         .apply(
             String.format("Write to Kafka topic '%s'", spec.getTopic()),

sdks/java/io/kafka/src/main/java/org/apache/beam/sdk/io/kafka/KafkaIO.java

@@ -648,6 +648,8 @@ public static <K, V> WriteRecords<K, V> writeRecords() {
     return new AutoValue_KafkaIO_WriteRecords.Builder<K, V>()
         .setProducerConfig(WriteRecords.DEFAULT_PRODUCER_PROPERTIES)
         .setEOS(false)
+        .setEosTriggerNumElements(1) // keep default numElements
+        .setEosTriggerTimeout(null) // keep default trigger (timeout)
         .setNumShards(0)
         .setConsumerFactoryFn(KafkaIOUtils.KAFKA_CONSUMER_FACTORY_FN)
         .setBadRecordRouter(BadRecordRouter.THROWING_ROUTER)
@@ -3185,6 +3187,10 @@ public abstract static class WriteRecords<K, V>
     @Pure
     public abstract boolean isEOS();
 
+    public abstract int getEosTriggerNumElements();
+
+    public abstract @Nullable Duration getEosTriggerTimeout();
+
     @Pure
     public abstract @Nullable String getSinkGroupId();
 
@@ -3221,6 +3227,10 @@ abstract Builder<K, V> setPublishTimestampFunction(
 
       abstract Builder<K, V> setEOS(boolean eosEnabled);
 
+      abstract Builder<K, V> setEosTriggerNumElements(int numElements);
+
+      abstract Builder<K, V> setEosTriggerTimeout(@Nullable Duration timeout);
+
       abstract Builder<K, V> setSinkGroupId(String sinkGroupId);
 
       abstract Builder<K, V> setNumShards(int numShards);
@@ -3368,6 +3378,15 @@ public WriteRecords<K, V> withEOS(int numShards, String sinkGroupId) {
       return toBuilder().setEOS(true).setNumShards(numShards).setSinkGroupId(sinkGroupId).build();
     }
 
+    public WriteRecords<K, V> withEOSTriggerConfig(int numElements, Duration timeout) {
+      checkArgument(numElements >= 1, "numElements should be >= 1");
+      checkArgument(timeout != null, "timeout is required for exactly-once sink");
+      return toBuilder()
+          .setEosTriggerNumElements(numElements)
+          .setEosTriggerTimeout(timeout)
+          .build();
+    }
+
     /**
      * When exactly-once semantics are enabled (see {@link #withEOS(int, String)}), the sink needs
      * to fetch previously stored state with Kafka topic. Fetching the metadata requires a consumer.
@@ -3653,6 +3672,19 @@ public Write<K, V> withEOS(int numShards, String sinkGroupId) {
       return withWriteRecordsTransform(getWriteRecordsTransform().withEOS(numShards, sinkGroupId));
     }
 
+    /**
+     * Set the frequency and numElements threshold at which messages are triggered.
+     *
+     * <p>This is only applicable when the write method is set to EOS.
+     *
+     * <p>Every timeout duration, or numElements (repeated, after first condition is met) collection
+     * of elements written.
+     */
+    public Write<K, V> withEOSTriggerConfig(int numElements, Duration timeout) {
+      return withWriteRecordsTransform(
+          getWriteRecordsTransform().withEOSTriggerConfig(numElements, timeout));
+    }
+
     /**
      * Wrapper method over {@link WriteRecords#withConsumerFactoryFn(SerializableFunction)}, used to
      * keep the compatibility with old API based on KV type of element.

sdks/java/io/kafka/upgrade/src/main/java/org/apache/beam/sdk/io/kafka/upgrade/KafkaIOTranslation.java

@@ -479,6 +479,8 @@ static class KafkaIOWriteTranslator implements TransformPayloadTranslator<Write<
             .addNullableByteArrayField("producer_factory_fn")
             .addNullableByteArrayField("publish_timestamp_fn")
             .addBooleanField("eos")
+            .addInt32Field("eos_trigger_num_elements")
+            .addNullableInt64Field("eos_trigger_timeout_ms")
             .addInt32Field("num_shards")
             .addNullableStringField("sink_group_id")
             .addNullableByteArrayField("consumer_factory_fn")
@@ -547,6 +549,11 @@ public Row toConfigRow(Write<?, ?> transform) {
       }
 
       fieldValues.put("eos", writeRecordsTransform.isEOS());
+      org.joda.time.Duration eosTriggerTimeout = writeRecordsTransform.getEosTriggerTimeout();
+      if (eosTriggerTimeout != null) {
+        fieldValues.put("eos_trigger_timeout_ms", eosTriggerTimeout.getMillis());
+      }
+      fieldValues.put("eos_trigger_num_elements", writeRecordsTransform.getEosTriggerNumElements());
       fieldValues.put("num_shards", writeRecordsTransform.getNumShards());
 
       if (writeRecordsTransform.getSinkGroupId() != null) {

sdks/java/io/kafka/upgrade/src/test/java/org/apache/beam/sdk/io/kafka/upgrade/KafkaIOTranslationTest.java

@@ -94,6 +94,8 @@ public class KafkaIOTranslationTest {
     WRITE_TRANSFORM_SCHEMA_MAPPING.put("getValueSerializer", "value_serializer");
     WRITE_TRANSFORM_SCHEMA_MAPPING.put("getPublishTimestampFunction", "publish_timestamp_fn");
     WRITE_TRANSFORM_SCHEMA_MAPPING.put("isEOS", "eos");
+    WRITE_TRANSFORM_SCHEMA_MAPPING.put("getEosTriggerTimeout", "eos_trigger_timeout_ms");
+    WRITE_TRANSFORM_SCHEMA_MAPPING.put("getEosTriggerNumElements", "eos_trigger_num_elements");
     WRITE_TRANSFORM_SCHEMA_MAPPING.put("getSinkGroupId", "sink_group_id");
     WRITE_TRANSFORM_SCHEMA_MAPPING.put("getNumShards", "num_shards");
     WRITE_TRANSFORM_SCHEMA_MAPPING.put("getConsumerFactoryFn", "consumer_factory_fn");