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https://issues.apache.org/jira/browse/HDFS-17863?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18053767#comment-18053767
]
ASF GitHub Bot commented on HDFS-17863:
---------------------------------------
hadoop-yetus commented on PR #8203:
URL: https://github.com/apache/hadoop/pull/8203#issuecomment-3788103798
:broken_heart: **-1 overall**
| Vote | Subsystem | Runtime | Logfile | Comment |
|:----:|----------:|--------:|:--------:|:-------:|
| +0 :ok: | reexec | 0m 47s | | Docker mode activated. |
|||| _ Prechecks _ |
| +1 :green_heart: | dupname | 0m 0s | | No case conflicting files
found. |
| +0 :ok: | codespell | 0m 0s | | codespell was not available. |
| +0 :ok: | detsecrets | 0m 0s | | detect-secrets was not available.
|
| +1 :green_heart: | @author | 0m 0s | | The patch does not contain
any @author tags. |
| +1 :green_heart: | test4tests | 0m 0s | | The patch appears to
include 1 new or modified test files. |
|||| _ trunk Compile Tests _ |
| +1 :green_heart: | mvninstall | 25m 41s | | trunk passed |
| +1 :green_heart: | compile | 0m 59s | | trunk passed with JDK
Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04 |
| +1 :green_heart: | compile | 0m 55s | | trunk passed with JDK
Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04 |
| +1 :green_heart: | checkstyle | 0m 39s | | trunk passed |
| +1 :green_heart: | mvnsite | 1m 7s | | trunk passed |
| +1 :green_heart: | javadoc | 0m 55s | | trunk passed with JDK
Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04 |
| +1 :green_heart: | javadoc | 0m 53s | | trunk passed with JDK
Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04 |
| +1 :green_heart: | spotbugs | 2m 8s | | trunk passed |
| +1 :green_heart: | shadedclient | 16m 38s | | branch has no errors
when building and testing our client artifacts. |
|||| _ Patch Compile Tests _ |
| +1 :green_heart: | mvninstall | 0m 44s | | the patch passed |
| +1 :green_heart: | compile | 0m 40s | | the patch passed with JDK
Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04 |
| +1 :green_heart: | javac | 0m 40s | | the patch passed |
| +1 :green_heart: | compile | 0m 40s | | the patch passed with JDK
Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04 |
| +1 :green_heart: | javac | 0m 40s | | the patch passed |
| +1 :green_heart: | blanks | 0m 0s | | The patch has no blanks
issues. |
| +1 :green_heart: | checkstyle | 0m 21s | | the patch passed |
| +1 :green_heart: | mvnsite | 0m 48s | | the patch passed |
| +1 :green_heart: | javadoc | 0m 34s | | the patch passed with JDK
Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04 |
| +1 :green_heart: | javadoc | 0m 34s | | the patch passed with JDK
Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04 |
| +1 :green_heart: | spotbugs | 1m 56s | | the patch passed |
| +1 :green_heart: | shadedclient | 16m 6s | | patch has no errors
when building and testing our client artifacts. |
|||| _ Other Tests _ |
| -1 :x: | unit | 174m 44s |
[/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt](https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8203/1/artifact/out/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt)
| hadoop-hdfs in the patch passed. |
| +1 :green_heart: | asflicense | 0m 27s | | The patch does not
generate ASF License warnings. |
| | | 248m 31s | | |
| Reason | Tests |
|-------:|:------|
| Failed junit tests | hadoop.hdfs.tools.TestDFSAdmin |
| Subsystem | Report/Notes |
|----------:|:-------------|
| Docker | ClientAPI=1.52 ServerAPI=1.52 base:
https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8203/1/artifact/out/Dockerfile
|
| GITHUB PR | https://github.com/apache/hadoop/pull/8203 |
| Optional Tests | dupname asflicense compile javac javadoc mvninstall
mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets |
| uname | Linux b04473ab70b6 5.15.0-164-generic #174-Ubuntu SMP Fri Nov 14
20:25:16 UTC 2025 x86_64 x86_64 x86_64 GNU/Linux |
| Build tool | maven |
| Personality | dev-support/bin/hadoop.sh |
| git revision | trunk / 405db4e6657c234a96852423d7a38ad4203d3862 |
| Default Java | Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04 |
| Multi-JDK versions |
/usr/lib/jvm/java-21-openjdk-amd64:Ubuntu-21.0.7+6-Ubuntu-0ubuntu120.04
/usr/lib/jvm/java-17-openjdk-amd64:Ubuntu-17.0.15+6-Ubuntu-0ubuntu120.04 |
| Test Results |
https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8203/1/testReport/ |
| Max. process+thread count | 4830 (vs. ulimit of 5500) |
| modules | C: hadoop-hdfs-project/hadoop-hdfs U:
hadoop-hdfs-project/hadoop-hdfs |
| Console output |
https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-8203/1/console |
| versions | git=2.25.1 maven=3.9.11 spotbugs=4.9.7 |
| Powered by | Apache Yetus 0.14.1 https://yetus.apache.org |
This message was automatically generated.
> CannotObtainBlockLengthException after DataNode restart
> -------------------------------------------------------
>
> Key: HDFS-17863
> URL: https://issues.apache.org/jira/browse/HDFS-17863
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: datanode, dfs, hdfs-client
> Affects Versions: 3.3.5
> Environment: Hadoop 3.3.5
> Java 8
> Maven 3.6.3
> Reporter: rstest
> Priority: Critical
> Labels: pull-request-available
> Attachments: reproduce.sh, restart.patch
>
>
> h2. DESCRIPTION:
> After hflush(), HDFS guarantees that written data becomes visible to readers,
> even while the file remains under construction. This guarantee is BROKEN after
> DataNode restart. Under-construction blocks that have been flushed become
> inaccessible (visible length = -1) until explicit lease recovery, causing
> CannotObtainBlockLengthException when clients try to read the file.
> This is a genuine production bug that affects:
> - HBase WAL recovery after DataNode failures
> - Streaming applications that write and read simultaneously
> - Any application relying on hflush() visibility guarantees
> h2. STEPS TO REPRODUCE:
> Download the `reproduce.sh` and `restart.patch`, then
> {code:java}
> $ bash reproduce.sh{code}
> The script:
> 1. Clones Hadoop repository (release 3.3.5 branch)
> 2. Applies test patch (restart.patch) that adds the reproduction test
> 3. Builds the Hadoop HDFS module
> 4. Runs test case:
> TestBlockToken#testLastLocatedBlockTokenExpiryWithDataNodeRestart
> *EXPECTED RESULT:*
> File should be readable after hflush(), even after DataNode restart
> *ACTUAL RESULT:*
> org.apache.hadoop.hdfs.CannotObtainBlockLengthException: Cannot obtain block
> length for LocatedBlock
> The bug is confirmed if the test fails with CannotObtainBlockLengthException.
> *KEY OBSERVATION:*
> - Tests with NameNode-only restart (no DataNode restart) DO NOT fail
> - The bug ONLY occurs when DataNode restarts
> h2. ROOT CAUSE:
> When a DataNode restarts, under-construction block replicas are loaded from
> disk and placed in ReplicaWaitingToBeRecovered (RWR) state:
> File: ReplicaWaitingToBeRecovered.java:75
> @Override
> public long getVisibleLength()
> { return -1; // no bytes are visible }
> This state explicitly returns -1 for visible length, meaning "no bytes
> visible"
> until lease recovery completes.
> When a client tries to open the file:
> 1. DFSInputStream calls readBlockLength() to determine UC block length
> 2. Contacts DataNode via getReplicaVisibleLength()
> 3. Receives -1 (not a valid length)
> 4. Treats this as a failure, tries next DataNode
> 5. All DataNodes return -1
> 6. Throws CannotObtainBlockLengthException
> The problem persists because:
> - Lease is still held by the original client (output stream still open)
> - Client is still alive (from HDFS's perspective)
> - Automatic lease recovery only triggers when lease holder is detected as
> dead
> - No mechanism to automatically recover in this scenario
> h2. *DIAGNOSTIC EVIDENCE:*
> BEFORE DataNode Restart:
> - File under construction: true
> - Block length: 6 bytes
> - Block is complete: false
> - DataNode replica visible length: 6 ✅ READABLE
> AFTER DataNode Restart:
> - File under construction: true
> - Block length: 6 bytes
> - Block is complete: false
> - DataNode replica visible length: -1 ❌ UNREADABLE!
> AFTER Explicit Lease Recovery:
> - File under construction: false
> - Block length: 6 bytes
> - Block is complete: true
> - DataNode replica visible length: 6 ✅ READABLE AGAIN!
> h2. WHY THIS IS A BUG (NOT EXPECTED BEHAVIOR):
> HDFS Guarantees:
> - hflush() ensures data is visible to new readers
> - Under-construction files should be readable after hflush()
> - This is the documented contract for hflush()
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