[KAFKA-13985] MirrorSourceTask commitRecord throws NPE if SMT is filtering out source record

• Type: Bug
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: 3.1.0, 3.2.0, 3.3.0
• Fix Version/s: 3.4.0
• Component/s: mirrormaker
• Assignee: Rens Groothuijsen
• Reporter: Jacopo Riciputi
• Created: 13/Jun/22 13:10
• Updated: 15/Sep/22 13:56
• Resolved: 15/Sep/22 13:56

Description

Applying a SMT that filters out messages it can brings to enter in this path:

From WorkerSourceTask.java

final SourceRecord record = transformationChain.apply(preTransformRecord);
final ProducerRecord<byte[], byte[]> producerRecord = convertTransformedRecord(record);
if (producerRecord == null || retryWithToleranceOperator.failed()) {
    counter.skipRecord();
    commitTaskRecord(preTransformRecord, null);
    continue;
} 

 

Then to:

private void commitTaskRecord(SourceRecord record, RecordMetadata metadata) {
        try {
            task.commitRecord(record, metadata);
        } catch (Throwable t) {
            log.error("{} Exception thrown while calling task.commitRecord()", this, t);
        }
}

Finally
From MirrorSourceTask.java

    @Override
    public void commitRecord(SourceRecord record, RecordMetadata metadata) {
        try {
            if (stopping) {
                return;
            }
            if (!metadata.hasOffset()) {
                log.error("RecordMetadata has no offset -- can't sync offsets for {}.", record.topic());
                return;
            }

...

 
Causing a NPE because metadata is null.
This the exception.

[2022-06-13 12:31:33,094] WARN Failure committing record. (org.apache.kafka.connect.mirror.MirrorSourceTask:190)
java.lang.NullPointerException
    at org.apache.kafka.connect.mirror.MirrorSourceTask.commitRecord(MirrorSourceTask.java:177)
    at org.apache.kafka.connect.runtime.WorkerSourceTask.commitTaskRecord(WorkerSourceTask.java:463)
    at org.apache.kafka.connect.runtime.WorkerSourceTask.sendRecords(WorkerSourceTask.java:358)
    at org.apache.kafka.connect.runtime.WorkerSourceTask.execute(WorkerSourceTask.java:257)
    at org.apache.kafka.connect.runtime.WorkerTask.doRun(WorkerTask.java:188)
    at org.apache.kafka.connect.runtime.WorkerTask.run(WorkerTask.java:243)
    at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Unknown Source)
    at java.base/java.util.concurrent.FutureTask.run(Unknown Source)
    at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
    at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
    at java.base/java.lang.Thread.run(Unknown Source) 

In my understanding this is well handled and it does not have negative impacts because it's handled by MirrorSourceTask.commitRecord, without leaving the exception be forwarded outside of it. 

But probably is preferred to handle it checking if metadata != null.
So skipping commit but safely and silently

[EDIT]
Actually, going a bit in deep, there is a small side-effect.

If the latest message elaborated was filtered out (so not committed by MirrorSourceTask), if MM2 instance is rebooted, this message will be re-read by consumer, because offset was not committed (and probably filtered out if configurations wasn't change).

But probably this behavior is fine considering MM2's nature

 

Issue Links

• duplicates: KAFKA-13632 MirrorMaker 2.0 NPE and Warning "Failure to commit records" for filtered records
• links to: GitHub Pull Request #12602