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https://issues.apache.org/jira/browse/HADOOP-19862?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18091409#comment-18091409
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ASF GitHub Bot commented on HADOOP-19862:
-----------------------------------------
konstantinb commented on PR #8426:
URL: https://github.com/apache/hadoop/pull/8426#issuecomment-4796446796
I ran the full hadoop-aws integration suite with all four shared pools off,
then on, matching the cloud_aws CI invocation (JDK 17; ./mvnw verify -B
-Dparallel-tests -Dscale=true), against both LocalStack (the CI endpoint) and
real S3 (us-east-1).
- Correctness: identical failing-test set with pools off vs on, on both
endpoints. The failures on my local are identical and appear environmental
(community-LocalStack emulation gaps; STS/delegation/Kerberos/ACL setup on the
test bucket) — none introduced by this change.
- Performance: no measurable regression. Pools-on matched pools-off on runs
identical to CI setup across repeated attempts, and on the operation-heavy
real-S3 paths I measured directly (commit protocols, recursive treewalk,
huge-file uploads).
So, enabling the shared pools neither changes results nor measurably affects
performance in these runs.
Unless someone objects, I will flip the defaults to ON tomorrow and ask for
reapprovals
> 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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