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https://issues.apache.org/jira/browse/KAFKA-19758?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18028354#comment-18028354
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Greg Harris commented on KAFKA-19758:
-------------------------------------
We did/should continue to have a policy of choosing the co-located plugin when
all else is equal, see KAFKA-8819. This has unintentionally regressed with
KIP-891 and should be fixed.
However my point was that this is a very brittle setup that will only work as
long as a plugin and it's connector are not isolated from one another (in the
same PluginClassLoader). As soon as they are isolated, or once someone uses
plugin.version to select another instance, or perhaps once a newer version is
installed, I would expect this to break again.
Mario, your example plugin path is an incorrect installation, because the
plugins are all in the same class loader (corresponding to the blue directory).
Only one version will be discovered, and it will be arbitrary based on
filesystem order. It is very likely that the different versions of the classes
collide and cause more serious problems, so Connect does not consider those
cases (and it's also distinct from the bug being discussed here). That directly
structure is meant to be used with `plugin.path=opt/plugins/blue/`.
> Weird behavior on Kafka Connect 4.1 class loading
> -------------------------------------------------
>
> Key: KAFKA-19758
> URL: https://issues.apache.org/jira/browse/KAFKA-19758
> Project: Kafka
> Issue Type: Bug
> Components: connect
> Affects Versions: 4.1.0
> Reporter: Mario Fiore Vitale
> Assignee: Mickael Maison
> Priority: Blocker
> Attachments: connect-service.log
>
>
> I have the
> [DebeziumOpenLineageEmitter|https://github.com/debezium/debezium/blob/main/debezium-openlineage/debezium-openlineage-api/src/main/java/io/debezium/openlineage/DebeziumOpenLineageEmitter.java]
> class in the *debezium-openlineage-api* that internally has a static map to
> maintain the registered emitter, the key of this map is
> "connectoLogicalName-taskid"
> Then there is the [OpenLineage
> SMT|https://github.com/debezium/debezium/blob/main/debezium-core/src/main/java/io/debezium/transforms/openlineage/OpenLineage.java],
> which is part of the *debezium-core.* In this SMT, I simply pass the same
> context to instantiate the same emitter via the connector.
> Now I'm running the following image
> {code:java}
> FROM quay.io/debezium/connect:3.3.0.Final
> ENV MAVEN_REPO="https://repo1.maven.org/maven2";
> ENV GROUP_ID="io/debezium"
> ENV DEBEZIUM_VERSION="3.3.0.Final"
> ENV ARTIFACT_ID="debezium-openlineage-core"
> ENV CLASSIFIER="-libs"
> COPY log4j.properties /kafka/config/log4j.properties
> Add OpenLineage
> RUN mkdir -p /tmp/openlineage-libs && \
> curl
> "$MAVEN_REPO/$GROUP_ID/$ARTIFACT_ID/$DEBEZIUM_VERSION/$ARTIFACT_ID-${DEBEZIUM_VERSION}${CLASSIFIER}.tar.gz"
> -o /tmp/debezium-openlineage-core-libs.tar.gz && \
> tar -xzvf /tmp/debezium-openlineage-core-libs.tar.gz -C
> /tmp/openlineage-libs --strip-components=1
> RUN cp -r /tmp/openlineage-libs/* /kafka/connect/debezium-connector-postgres/
> RUN cp -r /tmp/openlineage-libs/* /kafka/connect/debezium-connector-mongodb/
> ADD openlineage.yml /kafka/ {code}
> So is practically debezium connect image with just openlineage jars copied
> into postgres and mongodb connector folders.
> When I register the PostgreSQL connector
> {code:java}
> {
> "name": "inventory-connector-postgres",
> "config": {
> "connector.class": "io.debezium.connector.postgresql.PostgresConnector",
> "tasks.max": "1",
> "database.hostname": "postgres",
> "database.port": "5432",
> "database.user": "postgres",
> "database.password": "postgres",
> "database.server.id": "184054",
> "database.dbname": "postgres",
> "topic.prefix": "inventory",
> "snapshot.mode": "initial",
> "schema.history.internal.kafka.bootstrap.servers": "kafka:9092",
> "schema.history.internal.kafka.topic": "schema-changes.inventory",
> "slot.name": "postgres",
> "openlineage.integration.enabled": "true",
> "openlineage.integration.config.file.path": "/kafka/openlineage.yml",
> "openlineage.integration.job.description": "This connector does cdc for
> products",
> "openlineage.integration.tags": "env=prod,team=cdc",
> "openlineage.integration.owners": "Mario=maintainer,John Doe=Data
> scientist,IronMan=superero",
> "transforms": "openlineage",
> "transforms.openlineage.type":
> "io.debezium.transforms.openlineage.OpenLineage"
> }
> } {code}
>
> I get the following error
> {code:java}
> 2025-10-03T14:22:09,761 ERROR ||
> WorkerSourceTask{id=inventory-connector-postgres-0} Task threw an uncaught
> and unrecoverable exception. Task is being killed and will not recover until
> manually restarted [org.apache.kafka.connect.runtime.WorkerTask]
> org.apache.kafka.connect.errors.ConnectException: Tolerance exceeded in error
> handler
> at
> org.apache.kafka.connect.runtime.errors.RetryWithToleranceOperator.execAndHandleError(RetryWithToleranceOperator.java:260)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.errors.RetryWithToleranceOperator.execute(RetryWithToleranceOperator.java:180)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.TransformationChain.apply(TransformationChain.java:58)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.sendRecords(AbstractWorkerSourceTask.java:415)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.execute(AbstractWorkerSourceTask.java:376)
> ~[connect-runtime-4.1.0.jar:?]
> at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:243)
> ~[connect-runtime-4.1.0.jar:?]
> at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:298)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.AbstractWorkerSourceTask.run(AbstractWorkerSourceTask.java:83)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.isolation.Plugins.lambda$withClassLoader$1(Plugins.java:254)
> ~[connect-runtime-4.1.0.jar:?]
> at
> java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:572)
> ~[?:?]
> at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:317)
> ~[?:?]
> at
> java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1144)
> ~[?:?]
> at
> java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:642)
> ~[?:?]
> at java.base/java.lang.Thread.run(Thread.java:1583) [?:?]
> Caused by: java.lang.IllegalStateException: DebeziumOpenLineageEmitter not
> initialized for connector ConnectorContext[connectorLogicalName=inventory,
> connectorName=postgresql, taskId=0, version=null, config=null]. Call init()
> first.
> at
> io.debezium.openlineage.DebeziumOpenLineageEmitter.getEmitter(DebeziumOpenLineageEmitter.java:176)
> ~[debezium-openlineage-api-3.3.0.Final.jar:3.3.0.Final]
> at
> io.debezium.openlineage.DebeziumOpenLineageEmitter.emit(DebeziumOpenLineageEmitter.java:153)
> ~[debezium-openlineage-api-3.3.0.Final.jar:3.3.0.Final]
> at
> io.debezium.transforms.openlineage.OpenLineage.apply(OpenLineage.java:74)
> ~[debezium-core-3.3.0.Final.jar:3.3.0.Final]
> at
> org.apache.kafka.connect.runtime.TransformationStage.apply(TransformationStage.java:95)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.TransformationChain.lambda$apply$0(TransformationChain.java:58)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.errors.RetryWithToleranceOperator.execAndRetry(RetryWithToleranceOperator.java:208)
> ~[connect-runtime-4.1.0.jar:?]
> at
> org.apache.kafka.connect.runtime.errors.RetryWithToleranceOperator.execAndHandleError(RetryWithToleranceOperator.java:244)
> ~[connect-runtime-4.1.0.jar:?]
> ... 13 more {code}
> Full logs [^connect-service.log]
>
> This is evidence that the emitters map is not shared between the connector
> and the SMT.
> The situation becomes weirder if I remove all connectors from the image
> except PostgreSQL and MongoDB.
> In that case, the PostgreSQL connector works perfectly.
> The plugins are in the folder */kafka/connect* (that is, the only
> `plugin.path` configured folder), each under a dedicated folder with their
> dependencies.
> I then started to add more connectors, and it continued to work until I added
> the SQL Server connector.
> To summarize, the problem arises when I put one or all of [sqlserver,
> spanner,vitess].
>
> The commonality for these connectors seems to be that they support
> multi-task. The others don't.
> Am I correct that Kafka Connect guarantees that each connector is loaded with
> an isolated class loader with its dependencies so that the static emitters
> should be shared between the Connector and the SMT?
> To add more, if I run the image from 3.2.0.Final (so Kafka 4.0.0) with all
> connectors, it works fine.
> I did other tests, and things are more and more weird. All tests were done
> with *{{plugin.path=/kafka/connect}}* and *KC 4.1*
> My original tests were with this directory structure
>
> {code:java}
> /kafka/connect
> |___ debezium-connector-postgres
> |___ debezium-connector-mongodb
> |___ debezium-connector-sqlserver{code}
>
> In this case, each connector should be isolated from each others (having a
> dedicated class loader). In that case, the sharing between the connector and
> SMT does not work for KC 4.0
> Then I tried with
>
> {code:java}
> /kafka/connect
> |___ debezium-connectors
> |___ debezium-connector-postgres
> |___ debezium-connector-mongodb
> |___ debezium-connector-sqlserver{code}
>
> So all connectors are not isolated and share the same class loader. In this
> case, no issue. And I'll say that this is expected.
> Then I tried with
>
> {code:java}
> /kafka/connect
> |___ debezium-connectors
> | |___ debezium-connector-postgres
> | |___ debezium-connector-mongodb
> |___ debezium-connector-sqlserver{code}
>
> where *{{postgres}}* and *{{mongodb}}* are not isolated (same classloader)
> and *{{sqlserver}}* is isolated (different classloader), and in this case, it
> still works. I expected this to fail as with the first setup.
> The SMT is in the *debezium-core* jar that and each connector has its own copy
> So in each connector folder, there are:
> {code:java}
> debezium-api-3.3.0.Final.jar
> debezium-common-3.3.0.Final.jar
> debezium-connector-[connectorName]-3.3.0.Final.jar
> debezium-core-3.3.0.Final.jar
> debezium-openlineage-api-3.3.0.Final.jar{code}
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