diff --git a/swh/journal/writer/kafka.py b/swh/journal/writer/kafka.py
--- a/swh/journal/writer/kafka.py
+++ b/swh/journal/writer/kafka.py
@@ -89,6 +89,9 @@
         will fail if some message deliveries are still pending.
       producer_class: override for the kafka producer class.
       anonymize: if True, activate the anonymization feature.
+      auto_flush: if True (default), flush the kafka producer in
+        ``write_addition()`` and ``write_additions()``. This should be set
+        to False ONLY for testing purpuse. DO NOT USE ON PRODUCTION ENVIRONMENT.
 
     """
 
@@ -102,10 +105,12 @@
         flush_timeout: float = 120,
         producer_class: Type[Producer] = Producer,
         anonymize: bool = False,
+        auto_flush: bool = True,
     ):
         self._prefix = prefix
         self._prefix_privileged = f"{self._prefix}_privileged"
         self.anonymize = anonymize
+        self.auto_flush = auto_flush
 
         if not producer_config:
             producer_config = {}
@@ -249,7 +254,8 @@
     def write_addition(self, object_type: str, object_: ValueProtocol) -> None:
         """Write a single object to the journal"""
         self._write_addition(object_type, object_)
-        self.flush()
+        if self.auto_flush:
+            self.flush()
 
     def write_additions(
         self, object_type: str, objects: Iterable[ValueProtocol]
@@ -258,4 +264,5 @@
         for object_ in objects:
             self._write_addition(object_type, object_)
 
-        self.flush()
+        if self.auto_flush:
+            self.flush()