From 6f87213fe965f0e825a700ba9fdf2db6dc2b2033 Mon Sep 17 00:00:00 2001
From: Gian Merlino <gianmerlino@gmail.com>
Date: Fri, 24 Apr 2026 16:00:08 -0700
Subject: [PATCH] feat: Include caller thread name in LimitedPoolIndexMerger
 threads.

In Indexers (CliIndexer), a thread pool LimitedPoolIndexMerger is used
to control the concurrency of IndexMerger operations and avoid
excessive memory usage. This patch updates the thread names of this
pool to reflect the calling thread, which will include the task ID.
---
 .../common/guava/ThreadRenamingRunnable.java  | 52 -------------------
 .../UnifiedIndexerAppenderatorsManager.java   | 36 ++++++++++---
 2 files changed, 28 insertions(+), 60 deletions(-)
 delete mode 100644 processing/src/main/java/org/apache/druid/common/guava/ThreadRenamingRunnable.java

diff --git a/processing/src/main/java/org/apache/druid/common/guava/ThreadRenamingRunnable.java b/processing/src/main/java/org/apache/druid/common/guava/ThreadRenamingRunnable.java
deleted file mode 100644
index 34446d74d8e9..000000000000
--- a/processing/src/main/java/org/apache/druid/common/guava/ThreadRenamingRunnable.java
+++ /dev/null
@@ -1,52 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License.  You may obtain a copy of the License at
- *
- *   http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-package org.apache.druid.common.guava;
-
-/**
- */
-public abstract class ThreadRenamingRunnable implements Runnable
-{
-  private final String name;
-
-  public ThreadRenamingRunnable(
-      String name
-  )
-  {
-    this.name = name;
-  }
-
-  @Override
-  public final void run()
-  {
-    final Thread currThread = Thread.currentThread();
-    String currName = currThread.getName();
-    try {
-      currThread.setName(name);
-      doRun();
-    }
-    finally {
-      currThread.setName(currName);
-    }
-
-  }
-
-  public abstract void doRun();
-}
-
diff --git a/server/src/main/java/org/apache/druid/segment/realtime/appenderator/UnifiedIndexerAppenderatorsManager.java b/server/src/main/java/org/apache/druid/segment/realtime/appenderator/UnifiedIndexerAppenderatorsManager.java
index 9eafd853d3f5..e6ee87f14cee 100644
--- a/server/src/main/java/org/apache/druid/segment/realtime/appenderator/UnifiedIndexerAppenderatorsManager.java
+++ b/server/src/main/java/org/apache/druid/segment/realtime/appenderator/UnifiedIndexerAppenderatorsManager.java
@@ -555,16 +555,26 @@ public File persist(
         @Nullable SegmentWriteOutMediumFactory segmentWriteOutMediumFactory
     )
     {
-      ListenableFuture<File> mergeFuture = mergeExecutor.submit(
-          () ->
-              baseMerger.persist(
+      // Include calling thread's name in the mergeExecutor thread name. This includes at least the task ID.
+      final String callerThreadName = Thread.currentThread().getName();
+      final ListenableFuture<File> mergeFuture = mergeExecutor.submit(
+          () -> {
+            final String runnableThreadName = Thread.currentThread().getName();
+            try {
+              Thread.currentThread().setName(runnableThreadName + "[" + callerThreadName + "]");
+              return baseMerger.persist(
                   index,
                   dataInterval,
                   outDir,
                   indexSpec,
                   progress,
                   segmentWriteOutMediumFactory
-              )
+              );
+            }
+            finally {
+              Thread.currentThread().setName(runnableThreadName);
+            }
+          }
       );
 
       try {
@@ -604,9 +614,14 @@ public File mergeQueryableIndex(
         int maxColumnsToMerge
     )
     {
-      ListenableFuture<File> mergeFuture = mergeExecutor.submit(
-          () ->
-              baseMerger.mergeQueryableIndex(
+      // Include calling thread's name in the mergeExecutor thread name. This includes at least the task ID.
+      final String callerThreadName = Thread.currentThread().getName();
+      final ListenableFuture<File> mergeFuture = mergeExecutor.submit(
+          () -> {
+            final String runnableThreadName = Thread.currentThread().getName();
+            try {
+              Thread.currentThread().setName(runnableThreadName + "[" + callerThreadName + "]");
+              return baseMerger.mergeQueryableIndex(
                   indexes,
                   rollup,
                   metricAggs,
@@ -617,7 +632,12 @@ public File mergeQueryableIndex(
                   new BaseProgressIndicator(),
                   segmentWriteOutMediumFactory,
                   maxColumnsToMerge
-              )
+              );
+            }
+            finally {
+              Thread.currentThread().setName(runnableThreadName);
+            }
+          }
       );
 
       try {