solution

quarkus-kafka-panache-generator/src/main/java/dev/struchkov/example/quarkus/generator/KafkaMessageGenerator.java

@@ -21,7 +21,7 @@ public class KafkaMessageGenerator {
 
 
     public void start(@Observes StartupEvent ev) {
-        for (int i = 0; i < 20; i++) {
+        for (int i = 0; i < 50; i++) {
             final KafkaMessage kafkaMessage = new KafkaMessage();
             kafkaMessage.setCount(i);
             telegramChannel.sendAndAwait(kafkaMessage);

quarkus-kafka-panache-problem/src/main/java/dev/struchkov/example/quarkus/kafka/EntityRepositoryImpl.java

@@ -0,0 +1,21 @@
+package dev.struchkov.example.quarkus.kafka;
+
+import io.smallrye.mutiny.Uni;
+import lombok.RequiredArgsConstructor;
+import org.hibernate.reactive.mutiny.Mutiny;
+
+import javax.enterprise.context.ApplicationScoped;
+
+@ApplicationScoped
+@RequiredArgsConstructor
+public class EntityRepositoryImpl {
+
+    private final Mutiny.SessionFactory factory;
+
+    public Uni<EntityForDb> save(EntityForDb entityForDb) {
+        return factory.withTransaction(
+                session -> session.merge(entityForDb)
+        );
+    }
+
+}

quarkus-kafka-panache-problem/src/main/java/dev/struchkov/example/quarkus/kafka/KafkaHandler.java

@@ -10,14 +10,14 @@ import javax.enterprise.context.ApplicationScoped;
 @RequiredArgsConstructor
 public class KafkaHandler {
 
-    private final PanacheRepositoryImpl panacheRepository;
+    private final EntityRepositoryImpl panacheRepository;
 
     @Incoming("test")
     public Uni<Void> handle(KafkaMessage message) {
         System.out.println("Получено сообщение " + message);
         final EntityForDb entityForDb = new EntityForDb();
         entityForDb.setCount(message.getCount());
-        return panacheRepository.persistAndFlush(entityForDb).replaceWithVoid();
+        return panacheRepository.save(entityForDb).replaceWithVoid();
     }
 
 }

quarkus-kafka-panache-problem/src/main/java/dev/struchkov/example/quarkus/kafka/PanacheRepositoryImpl.java

@@ -1,10 +0,0 @@
-package dev.struchkov.example.quarkus.kafka;
-
-import io.quarkus.hibernate.reactive.panache.PanacheRepository;
-
-import javax.enterprise.context.ApplicationScoped;
-
-@ApplicationScoped
-public class PanacheRepositoryImpl implements PanacheRepository<EntityForDb> {
-
-}

quarkus-kafka-panache-problem/src/main/resources/application.yml

@@ -6,6 +6,7 @@ quarkus:
     jdbc: false
     reactive:
       url: postgresql://localhost:5432/quarkus_test
+      max-size: 20
   hibernate-orm:
     database:
       generation: update