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https://issues.apache.org/jira/browse/HADOOP-19862?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18090745#comment-18090745
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ASF GitHub Bot commented on HADOOP-19862:
-----------------------------------------
konstantinb commented on code in PR #8426:
URL: https://github.com/apache/hadoop/pull/8426#discussion_r3455709416
##########
hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/s3a/ITestS3ASharedThreadPoolDisabled.java:
##########
@@ -0,0 +1,74 @@
+/*
+ * 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.hadoop.fs.s3a;
+
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Control case for {@link ITestS3ASharedThreadPoolEnabled}: with the shared
+ * pool disabled (the default), each S3AFileSystem's AWS SDK clients create
their
+ * own sdk-ScheduledExecutor pool, so thread count grows with the number of
+ * instances. Kept a separate class so it runs in its own JVM (hadoop-aws uses
+ * reuseForks=false) and the static holders never memoize in the enabled state.
Review Comment:
Thank you @ajfabbri!
Exactly the case I had in mind for spelling it out. Worth noting it's a
per-process need, not per-thread: the holder is a JVM-global static, so these
two want separate JVMs (the reuseForks axis), not just serialized threads — an
ExecutionMode-style knob would need to drive fork allocation to cover it. FWIW
I prototyped that side: each test launches a child JVM (ProcessBuilder, much
like the router tests' JavaProcess) that reuses the same S3ATestUtils
measurement, so the work runs with fresh statics and comes out reuseForks-immune
[SharedPoolForkWorker.java](https://github.com/user-attachments/files/29225451/SharedPoolForkWorker.java)
[ITestS3ASharedThreadPoolEnabledForked.java](https://github.com/user-attachments/files/29225480/ITestS3ASharedThreadPoolEnabledForked.java)
[ITestS3ASharedThreadPoolDisabledForked.java](https://github.com/user-attachments/files/29225498/ITestS3ASharedThreadPoolDisabledForked.java)
> S3A: Thread leak from AWS SDK v2 ScheduledExecutorService
> ---------------------------------------------------------
>
> Key: HADOOP-19862
> URL: https://issues.apache.org/jira/browse/HADOOP-19862
> Project: Hadoop Common
> Issue Type: Bug
> Reporter: Konstantin Bereznyakov
> Priority: Major
> Labels: pull-request-available
>
> AWS SDK v2 S3 clients create internal ScheduledExecutorService instances that
> accumulate over time, causing unbounded thread growth. Thread dumps show
> thousands of sdk-ScheduledExecutor-* threads in processes that create
> multiple S3AFileSystem instances.
> Environment
> - Hadoop 3.4.x with AWS SDK v2
> - Not observed in Hadoop 3.3.x (AWS SDK v1)
> Observed Behavior
> Thread dump comparison:
> Hadoop 3.3.x (AWS SDK v1): Normal thread count
> Hadoop 3.4.x (AWS SDK v2): 1600+ "sdk-ScheduledExecutor-*" threads
> Thread pattern:
> "sdk-ScheduledExecutor-0-0" daemon prio=5 waiting
> "sdk-ScheduledExecutor-0-1" daemon prio=5 waiting
> ...
> "sdk-ScheduledExecutor-0-4" daemon prio=5 waiting
> "sdk-ScheduledExecutor-1-0" daemon prio=5 waiting
> ...
> Root Cause
> AWS SDK v2's SdkDefaultClientBuilder creates a ScheduledThreadPoolExecutor
> with 5 threads per client when no executor is explicitly provided
> (https://github.com/aws/aws-sdk-java-v2/issues/1690):
> Executors.newScheduledThreadPool(5,
> new
> ThreadFactoryBuilder().threadNamePrefix("sdk-ScheduledExecutor").build())
> These threads are used for retry scheduling, timeout handling, and
> credential refresh.
> Contributing Factors
> 1. AbstractFileSystem has no caching
> Unlike FileSystem.get() which uses CACHE.get(uri, conf),
> AbstractFileSystem.get() always creates new instances:
> // AbstractFileSystem.java:263-266
> public static AbstractFileSystem get(final URI uri, final Configuration
> conf) {
> return createFileSystem(uri, conf); // NO CACHING
> }
> Each FileContext.getFileContext() call with an S3 URI creates:
> - New AbstractFileSystem (S3A)
> - New S3AFileSystem
> - New S3Client
> - 5 new sdk-ScheduledExecutor threads
> 2. S3Client threads not released on close
> As documented in https://github.com/aws/aws-sdk-java-v2/issues/1690:
> "When using cached, ephemeral clients, I can see that the scheduled thread
> pool will at times be leaked when the aws client is evicted"
> 3. Multiple client types affected
> S3A creates multiple AWS SDK clients:
> - S3Client (sync)
> - S3AsyncClient
> - STS client (for delegation tokens)
> - KMS client (for encryption)
> Each client instance creates its own 5-thread pool.
> Impact
> - Unbounded thread growth in any process using S3A
> - Resource exhaustion leading to OOM or system instability
> - Particularly affects YARN NodeManager, Spark drivers/executors, and other
> services that create many filesystem instances
> Related
> - https://github.com/aws/aws-sdk-java-v2/issues/1690 - SDK issue
> documenting the problem
> - https://github.com/aws/aws-sdk-java-v2/pull/4002 - SDK fix allowing
> shared executor configuration
> - HADOOP-19624 - Similar thread leak in ABFS (AbfsClientThrottlingAnalyzer)
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