Hongshun Wang created FLINK-40202:
-------------------------------------
Summary: HybridSplitAssigner may initialize enumerator metrics
concurrently with snapshot split assignment
Key: FLINK-40202
URL: https://issues.apache.org/jira/browse/FLINK-40202
Project: Flink
Issue Type: Bug
Components: Flink CDC
Affects Versions: cdc-3.5.0
Reporter: Hongshun Wang
Fix For: cdc-3.6.0
h3. Problem
{{The issue has been observed with the following exception:}}
{code:java}
java.util.ConcurrentModificationException: null
at java.util.ArrayList$Itr.checkForComodification(ArrayList.java:1043)
~[?:?]
at java.util.ArrayList$Itr.next(ArrayList.java:997) ~[?:?]
at
org.apache.flink.cdc.connectors.base.source.assigner.SnapshotSplitAssigner.initEnumeratorMetrics(SnapshotSplitAssigner.java:305)
~[ververica-connector-sqlserver-1.20-vvr-11.7.0-4-jdk11-jar-with-dependencies.jar:1.20-vvr-11.7.0-4-jdk11]
{code}
{{}}
h3. *Root Cause*
h3. HybridSplitAssigner#open
{code:java}
snapshotSplitAssigner.open();
// init enumerator metrics
snapshotSplitAssigner.initEnumeratorMetrics(enumeratorMetrics); {code}
{{SnapshotSplitAssigner#open}}
{code:java}
chunkSplitter.open();
discoveryCaptureTables();
captureNewlyAddedTables();
startAsynchronouslySplit(); {code}
{{}}
# `SnapshotSplitAssigner#open` starts asynchronous snapshot splitting via
`startAsynchronouslySplit()`.
# enumerator metrics are initialized only after
`snapshotSplitAssigner.open()` returns.
# This leaves a race window where the background splitting thread can mutate
split state while `initEnumeratorMetrics()` is traversing it.
In the observed failure, the concurrent modification happens while iterating an
`ArrayList`, resulting in `ConcurrentModificationException`.
h3. {{}}
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