diff --git a/quickwit/quickwit-indexing/src/actors/indexing_service.rs b/quickwit/quickwit-indexing/src/actors/indexing_service.rs
index df71cc92ea4..26756c92086 100644
--- a/quickwit/quickwit-indexing/src/actors/indexing_service.rs
+++ b/quickwit/quickwit-indexing/src/actors/indexing_service.rs
@@ -27,8 +27,8 @@ use async_trait::async_trait;
 use futures::TryStreamExt;
 use itertools::Itertools;
 use quickwit_actors::{
-    Actor, ActorContext, ActorExitStatus, ActorHandle, ActorState, Handler, Healthz, Mailbox,
-    Observation,
+    Actor, ActorContext, ActorExitStatus, ActorHandle, ActorState, Command, Handler, Healthz,
+    Mailbox, Observation,
 };
 use quickwit_cluster::Cluster;
 use quickwit_common::fs::get_cache_directory_path;
@@ -504,21 +504,27 @@ impl IndexingService {
                 .merge_pipeline_handles
                 .remove_entry(&merge_pipeline_to_shutdown)
             {
-                // We kill the merge pipeline to avoid waiting a merge operation to finish as it can
-                // be long.
+                // We gracefully shutdown the merge pipeline, so we can complete the in-flight
+                // merges.
                 info!(
                     index_uid=%merge_pipeline_to_shutdown.index_uid,
                     source_id=%merge_pipeline_to_shutdown.source_id,
-                    "no more indexing pipeline on this index and source, killing merge pipeline"
+                    "shutting down orphan merge pipeline"
                 );
-                merge_pipeline_handle.handle.kill().await;
+                // The queue capacity of the merge pipeline is unbounded, so `.send_message(...)`
+                // should not block.
+                // We avoid using `.quit()` here because it waits for the actor to exit.
+                merge_pipeline_handle
+                    .handle
+                    .mailbox()
+                    .send_message(Command::Quit)
+                    .await
+                    .expect("merge pipeline mailbox should not be full");
             }
         }
-        // Finally remove the merge pipeline with an exit status.
+        // Finally, we remove the completed or failed merge pipelines.
         self.merge_pipeline_handles
-            .retain(|_, merge_pipeline_mailbox_handle| {
-                merge_pipeline_mailbox_handle.handle.state().is_running()
-            });
+            .retain(|_, merge_pipeline_handle| merge_pipeline_handle.handle.state().is_running());
         self.counters.num_running_merge_pipelines = self.merge_pipeline_handles.len();
         self.update_chitchat_running_plan().await;
 
@@ -543,23 +549,23 @@ impl IndexingService {
         immature_splits_opt: Option<Vec<SplitMetadata>>,
         ctx: &ActorContext<Self>,
     ) -> Result<Mailbox<MergePlanner>, IndexingError> {
-        if let Some(merge_pipeline_mailbox_handle) = self
+        if let Some(merge_pipeline_handle) = self
             .merge_pipeline_handles
             .get(&merge_pipeline_params.pipeline_id)
         {
-            return Ok(merge_pipeline_mailbox_handle.mailbox.clone());
+            return Ok(merge_pipeline_handle.mailbox.clone());
         }
         let merge_pipeline_id = merge_pipeline_params.pipeline_id.clone();
         let merge_pipeline =
             MergePipeline::new(merge_pipeline_params, immature_splits_opt, ctx.spawn_ctx());
         let merge_planner_mailbox = merge_pipeline.merge_planner_mailbox().clone();
         let (_pipeline_mailbox, pipeline_handle) = ctx.spawn_actor().spawn(merge_pipeline);
-        let merge_pipeline_mailbox_handle = MergePipelineHandle {
+        let merge_pipeline_handle = MergePipelineHandle {
             mailbox: merge_planner_mailbox.clone(),
             handle: pipeline_handle,
         };
         self.merge_pipeline_handles
-            .insert(merge_pipeline_id, merge_pipeline_mailbox_handle);
+            .insert(merge_pipeline_id, merge_pipeline_handle);
         self.counters.num_running_merge_pipelines += 1;
         Ok(merge_planner_mailbox)
     }
diff --git a/quickwit/quickwit-indexing/src/actors/merge_pipeline.rs b/quickwit/quickwit-indexing/src/actors/merge_pipeline.rs
index 2e3475f5759..a539329a833 100644
--- a/quickwit/quickwit-indexing/src/actors/merge_pipeline.rs
+++ b/quickwit/quickwit-indexing/src/actors/merge_pipeline.rs
@@ -251,7 +251,7 @@ impl MergePipeline {
             Some(self.merge_planner_mailbox.clone()),
             None,
         );
-        let (merge_publisher_mailbox, merge_publisher_handler) = ctx
+        let (merge_publisher_mailbox, merge_publisher_handle) = ctx
             .spawn_actor()
             .set_kill_switch(self.kill_switch.clone())
             .set_backpressure_micros_counter(
@@ -271,7 +271,7 @@ impl MergePipeline {
             self.params.max_concurrent_split_uploads,
             self.params.event_broker.clone(),
         );
-        let (merge_uploader_mailbox, merge_uploader_handler) = ctx
+        let (merge_uploader_mailbox, merge_uploader_handle) = ctx
             .spawn_actor()
             .set_kill_switch(self.kill_switch.clone())
             .spawn(merge_uploader);
@@ -279,7 +279,7 @@ impl MergePipeline {
         // Merge Packager
         let tag_fields = self.params.doc_mapper.tag_named_fields()?;
         let merge_packager = Packager::new("MergePackager", tag_fields, merge_uploader_mailbox);
-        let (merge_packager_mailbox, merge_packager_handler) = ctx
+        let (merge_packager_mailbox, merge_packager_handle) = ctx
             .spawn_actor()
             .set_kill_switch(self.kill_switch.clone())
             .spawn(merge_packager);
@@ -300,7 +300,7 @@ impl MergePipeline {
             merge_executor_io_controls,
             merge_packager_mailbox,
         );
-        let (merge_executor_mailbox, merge_executor_handler) = ctx
+        let (merge_executor_mailbox, merge_executor_handle) = ctx
             .spawn_actor()
             .set_kill_switch(self.kill_switch.clone())
             .set_backpressure_micros_counter(
@@ -316,7 +316,7 @@ impl MergePipeline {
             executor_mailbox: merge_executor_mailbox,
             io_controls: split_downloader_io_controls,
         };
-        let (merge_split_downloader_mailbox, merge_split_downloader_handler) = ctx
+        let (merge_split_downloader_mailbox, merge_split_downloader_handle) = ctx
             .spawn_actor()
             .set_kill_switch(self.kill_switch.clone())
             .set_backpressure_micros_counter(
@@ -334,7 +334,7 @@ impl MergePipeline {
             merge_split_downloader_mailbox,
             self.params.merge_scheduler_service.clone(),
         );
-        let (_, merge_planner_handler) = ctx
+        let (_, merge_planner_handle) = ctx
             .spawn_actor()
             .set_kill_switch(self.kill_switch.clone())
             .set_mailboxes(
@@ -346,12 +346,12 @@ impl MergePipeline {
         self.previous_generations_statistics = self.statistics.clone();
         self.statistics.generation += 1;
         self.handles_opt = Some(MergePipelineHandles {
-            merge_planner: merge_planner_handler,
-            merge_split_downloader: merge_split_downloader_handler,
-            merge_executor: merge_executor_handler,
-            merge_packager: merge_packager_handler,
-            merge_uploader: merge_uploader_handler,
-            merge_publisher: merge_publisher_handler,
+            merge_planner: merge_planner_handle,
+            merge_split_downloader: merge_split_downloader_handle,
+            merge_executor: merge_executor_handle,
+            merge_packager: merge_packager_handle,
+            merge_uploader: merge_uploader_handle,
+            merge_publisher: merge_publisher_handle,
             next_check_for_progress: Instant::now() + *HEARTBEAT,
         });
         Ok(())
@@ -359,14 +359,14 @@ impl MergePipeline {
 
     async fn terminate(&mut self) {
         self.kill_switch.kill();
-        if let Some(handlers) = self.handles_opt.take() {
+        if let Some(handles) = self.handles_opt.take() {
             tokio::join!(
-                handlers.merge_planner.kill(),
-                handlers.merge_split_downloader.kill(),
-                handlers.merge_executor.kill(),
-                handlers.merge_packager.kill(),
-                handlers.merge_uploader.kill(),
-                handlers.merge_publisher.kill(),
+                handles.merge_planner.kill(),
+                handles.merge_split_downloader.kill(),
+                handles.merge_executor.kill(),
+                handles.merge_packager.kill(),
+                handles.merge_uploader.kill(),
+                handles.merge_publisher.kill(),
             );
         }
     }
@@ -576,8 +576,8 @@ mod tests {
             event_broker: Default::default(),
         };
         let pipeline = MergePipeline::new(pipeline_params, None, universe.spawn_ctx());
-        let (_pipeline_mailbox, pipeline_handler) = universe.spawn_builder().spawn(pipeline);
-        let (pipeline_exit_status, pipeline_statistics) = pipeline_handler.quit().await;
+        let (_pipeline_mailbox, pipeline_handle) = universe.spawn_builder().spawn(pipeline);
+        let (pipeline_exit_status, pipeline_statistics) = pipeline_handle.quit().await;
         assert_eq!(pipeline_statistics.generation, 1);
         assert_eq!(pipeline_statistics.num_spawn_attempts, 1);
         assert_eq!(pipeline_statistics.num_published_splits, 0);