Priyesh K created HDDS-15783:
--------------------------------
Summary: ScmListCodec fails to deserialize empty lists from Ratis
log due to java.lang.Object element type regression
Key: HDDS-15783
URL: https://issues.apache.org/jira/browse/HDDS-15783
Project: Apache Ozone
Issue Type: Bug
Components: SCM, SCM HA
Reporter: Priyesh K
Assignee: Priyesh K
During an SCM HA cluster upgrade, SCM fails while replaying the Ratis log with
the following error:
{code:java}
2026-07-05 10:00:12,699 ERROR
[36209121-a632-4067-a36d-a6e0194cd83e@group-65230FEE3C3A-StateMachineUpdater]-org.apache.ratis.statemachine.StateMachine:
Terminating with exit status 1: Failed to resolve
java.lang.Objectorg.apache.ratis.thirdparty.com.google.protobuf.InvalidProtocolBufferException:
Failed to resolve java.lang.Object at
org.apache.hadoop.hdds.scm.ha.io.ScmCodecFactory$ClassResolver.get(ScmCodecFactory.java:177)
at
org.apache.hadoop.hdds.scm.ha.io.ScmCodecFactory$ClassResolver.get(ScmCodecFactory.java:147)
at
org.apache.hadoop.hdds.scm.ha.io.ScmListCodec.deserialize(ScmListCodec.java:72)
at
org.apache.hadoop.hdds.scm.ha.SCMRatisRequest.decode(SCMRatisRequest.java:154)
at
org.apache.hadoop.hdds.scm.ha.SCMStateMachine.applyTransaction(SCMStateMachine.java:146)
at
org.apache.ratis.server.impl.RaftServerImpl.applyLogToStateMachine(RaftServerImpl.java:1888)
at
org.apache.ratis.server.impl.StateMachineUpdater.applyLog(StateMachineUpdater.java:255)
at
org.apache.ratis.server.impl.StateMachineUpdater.run(StateMachineUpdater.java:194)
at java.base/java.lang.Thread.run(Thread.java:833)2026-07-05 10:00:12,702
INFO
[shutdown-hook-0]-org.apache.hadoop.hdds.scm.server.StorageContainerManagerStarter:
SHUTDOWN_MSG: {code}
*Root cause*
An empty List/ArrayList was written into the SCM Ratis log, and the new
ScmListCodec cannot deserialize it.On serialize, empty lists are stored with
element type java.lang.Object. On deserialize, the codec always tries to
resolve that type and get an element codec — even when there are zero
elements.This is a regression from the reflection-based codec refactor
([HDDS-14740 |https://issues.apache.org/jira/browse/HDDS-14740 ]/ [HDDS-14846|
https://issues.apache.org/jira/browse/HDDS-14846
]). The old ListCodec had the same Object.class sentinel on serialize, but on
deserialize it only loaded the element codec inside the value loop
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