Added support of topic messages batching

topic/src/main/java/tech/ydb/topic/read/impl/Batch.java

@@ -47,4 +47,12 @@ public boolean isDecompressed() {
     public void setDecompressed(boolean decompressed) {
         this.decompressed = decompressed;
     }
+
+    long getFirstCommitOffsetFrom() {
+        return messages.get(0).getCommitOffsetFrom();
+    }
+
+    long getLastOffset() {
+        return messages.get(messages.size() - 1).getOffset();
+    }
 }

topic/src/main/java/tech/ydb/topic/read/impl/PartitionSessionImpl.java

@@ -45,6 +45,7 @@ public class PartitionSessionImpl {
     private final PartitionSession sessionInfo;
     private final Executor decompressionExecutor;
     private final AtomicBoolean isWorking = new AtomicBoolean(true);
+    private final int maxBatchSize;
 
     private final Queue<Batch> decodingBatches = new LinkedList<>();
     private final ReentrantLock decodingBatchesLock = new ReentrantLock();
@@ -60,6 +61,7 @@ public class PartitionSessionImpl {
 
     private PartitionSessionImpl(Builder builder) {
         this.id = builder.id;
+        this.maxBatchSize = builder.maxBatchSize;
         this.fullId = builder.fullId;
         this.topicPath = builder.topicPath;
         this.consumerName = builder.consumerName;
@@ -308,21 +310,45 @@ private void sendDataToReadersIfNeeded() {
             return;
         }
         if (isReadingNow.compareAndSet(false, true)) {
-            Batch batchToRead = readingQueue.poll();
-            if (batchToRead == null) {
+            List<Batch> batchesToRead = new ArrayList<>();
+
+            Batch next = readingQueue.poll();
+            if (next == null) {
                 isReadingNow.set(false);
                 return;
             }
+
+            batchesToRead.add(next);
+            List<Message> messagesToRead = new ArrayList<>(next.getMessages());
+            long commitFrom = next.getFirstCommitOffsetFrom();
+            long commitTo = next.getLastOffset() + 1;
+
+            int batchSize = messagesToRead.size();
+            while (maxBatchSize <= 0 || batchSize < maxBatchSize) {
+                next = readingQueue.peek();
+                if (next == null) {
+                    break;
+                }
+                if (maxBatchSize > 0 && next.getMessages().size() + batchSize > maxBatchSize) {
+                    break;
+                }
+
+                next = readingQueue.poll();
+
+                batchesToRead.add(next);
+                messagesToRead.addAll(next.getMessages());
+                batchSize += next.getMessages().size();
+                commitTo = next.getLastOffset() + 1;
+            }
+
             // Should be called maximum in 1 thread at a time
-            List<MessageImpl> messageImplList = batchToRead.getMessages();
-            List<Message> messagesToRead = new ArrayList<>(messageImplList);
-            OffsetsRange offsetsToCommit = new OffsetsRangeImpl(messageImplList.get(0).getCommitOffsetFrom(),
-                    messageImplList.get(messageImplList.size() - 1).getOffset() + 1);
+            OffsetsRange offsetsToCommit = new OffsetsRangeImpl(commitFrom, commitTo);
             DataReceivedEvent event = new DataReceivedEventImpl(this, messagesToRead, offsetsToCommit);
             if (logger.isDebugEnabled()) {
                 logger.debug("[{}] DataReceivedEvent callback with {} message(s) (offsets {}-{}) is about " +
-                                "to be called...", fullId, messagesToRead.size(), messagesToRead.get(0).getOffset(),
-                        messagesToRead.get(messagesToRead.size() - 1).getOffset());
+                                "to be called...", fullId, messagesToRead.size(),
+                                    messagesToRead.get(0).getOffset(),
+                                    messagesToRead.get(messagesToRead.size() - 1).getOffset());
             }
             dataEventCallback.apply(event)
                     .whenComplete((res, th) -> {
@@ -338,7 +364,7 @@ private void sendDataToReadersIfNeeded() {
                                     messagesToRead.get(messagesToRead.size() - 1).getOffset());
                         }
                         isReadingNow.set(false);
-                        batchToRead.complete();
+                        batchesToRead.forEach(Batch::complete);
                         sendDataToReadersIfNeeded();
                     });
         } else {
@@ -376,6 +402,7 @@ public void shutdown() {
      */
     public static class Builder {
         private long id;
+        private int maxBatchSize;
         private String fullId;
         private String topicPath;
         private String consumerName;
@@ -391,6 +418,11 @@ public Builder setId(long id) {
             return this;
         }
 
+        public Builder setMaxBatchSize(int maxBatchSize) {
+            this.maxBatchSize = maxBatchSize;
+            return this;
+        }
+
         public Builder setFullId(String fullId) {
             this.fullId = fullId;
             return this;

topic/src/main/java/tech/ydb/topic/read/impl/ReaderImpl.java

@@ -402,6 +402,7 @@ private void onStartPartitionSessionRequest(YdbTopic.StreamReadMessage.StartPart
 
             PartitionSessionImpl partitionSession = PartitionSessionImpl.newBuilder()
                     .setId(partitionSessionId)
+                    .setMaxBatchSize(settings.getMaxBatchSize())
                     .setFullId(partitionSessionFullId)
                     .setTopicPath(request.getPartitionSession().getPath())
                     .setConsumerName(consumerName)

topic/src/main/java/tech/ydb/topic/settings/ReaderSettings.java

@@ -22,6 +22,7 @@ public class ReaderSettings {
     private final String readerName;
     private final List<TopicReadSettings> topics;
     private final long maxMemoryUsageBytes;
+    private final int maxBatchSize;
     private final Executor decompressionExecutor;
     private final BiConsumer<Status, Throwable> errorsHandler;
 
@@ -31,6 +32,7 @@ private ReaderSettings(Builder builder) {
         this.readerName = builder.readerName;
         this.topics = ImmutableList.copyOf(builder.topics);
         this.maxMemoryUsageBytes = builder.maxMemoryUsageBytes;
+        this.maxBatchSize = builder.maxBatchSize;
         this.decompressionExecutor = builder.decompressionExecutor;
         this.errorsHandler = builder.errorsHandler;
     }
@@ -60,6 +62,10 @@ public long getMaxMemoryUsageBytes() {
         return maxMemoryUsageBytes;
     }
 
+    public int getMaxBatchSize() {
+        return maxBatchSize;
+    }
+
     public Executor getDecompressionExecutor() {
         return decompressionExecutor;
     }
@@ -78,6 +84,7 @@ public static class Builder {
         private String readerName = null;
         private List<TopicReadSettings> topics = new ArrayList<>();
         private long maxMemoryUsageBytes = MAX_MEMORY_USAGE_BYTES_DEFAULT;
+        private int maxBatchSize = 0;
         private Executor decompressionExecutor = null;
         private BiConsumer<Status, Throwable> errorsHandler = null;
 
@@ -133,6 +140,11 @@ public Builder setMaxMemoryUsageBytes(long maxMemoryUsageBytes) {
             return this;
         }
 
+        public Builder setMaxBatchSize(int maxBatchSize) {
+            this.maxBatchSize = maxBatchSize;
+            return this;
+        }
+
         public Builder setErrorsHandler(BiConsumer<Status, Throwable> handler) {
             this.errorsHandler = handler;
             return this;