Status

Current state: Under DiscussionAccepted

Discussion thread: here 

JIRA: here 

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    /**
     * <p>
     * Commit an individual {@link SourceRecord} when the callback from the producer client is received. This method is
     * also called when a record is filtered by a transformation or when {@link ConnectorConfig} "errors.tolerance" is set to "all"
     * and thus will never be ACK'd by a broker.
     * In both cases {@code metadata} will be null.
     * </p>
     * <p>
     * SourceTasks are not required to implement this functionality; Kafka Connect will record offsets
     * automatically. This hook is provided for systems that also need to store offsets internally
     * in their own system.
     * </p>
     * <p>
     * The default implementation just calls {@link #commitRecord(SourceRecord)}, which is a nop by default. It is
     * not necessary to implement both methods.
     * </p>
     *
     * @param record {@link SourceRecord} that was successfully sent via the producer, filtered by a transformation, or dropped on producer exception
     * @param metadata {@link RecordMetadata} record metadata returned from the broker, or null if the record was filtered or if producer exceptions are ignored
     * @throws InterruptedException
     */
    public void commitRecord(SourceRecord record, RecordMetadata metadata)
            throws InterruptedException {
        // by default, just call other method for backwards compatibility
        commitRecord(record);
    }

Other Changes

The behavior of errors.tolerance will change with this update! Current connectors should expect to be able to recover from producer exceptions if they are set to all. See compatibility and migration section below.

WorkerSourceTask.java

			producer.send(
                    producerRecord,
                    (recordMetadata, e) -> {
                        if (e != null) {
                            log.error("{} failed to send record to {}: ", WorkerSourceTask.this, topic, e);
                            log.trace("{} Failed record: {}", WorkerSourceTask.this, preTransformRecord);
                            if (retryWithToleranceOperator.withinToleranceLimits(getErrorToleranceType().equals(ToleranceType.ALL)) {
                                                 commitTaskRecord(preTransformRecord, null);
                            }
                            else {
                                producerSendException.compareAndSet(null, e);
                            }

Proposed Changes

On kafka producer failure, WorkerSourceTask will check 

retryWithToleranceOperator.withinToleranceLimits()

to see if it should “ignore” this exception, call commitRecord(SourceRecord, RecordMetadata) to allow the connector to ack their source system, and continue processing. Otherwise it will set the producerSendException and the current behavior applies.

Setting "errors.tolerance" to "all" enables the functionality to skip records on producer write failure.

Compatibility, Deprecation, and Migration Plan

RetryWithToleranceOperator.java

    // For source connectors that want to skip kafka producer errors.
    // They cannot use withinToleranceLimits() as no failure may have actually occurred prior to the producer failing
    // to write to kafka.
    public synchronized ToleranceType getErrorToleranceType() {
        return errorToleranceType;
    }

Proposed Changes

A getter method will be added to RetryWithToleranceOperator that the WorkerSourceTask will check before allowing producer write errors to kafka to be skipped and acked by the source connector.

On kafka producer failure, WorkerSourceTask will check 

retryWithToleranceOperator.getErrorToleranceType().equals(ToleranceType.ALL)

to see if it should “ignore” this exception, call commitRecord(SourceRecord, RecordMetadata) to allow the connector to ack their source system, and continue processing. Otherwise it will set the producerSendException and the current behavior applies.

Setting "errors.tolerance" to "all" enables the functionality to skip records on producer write failure.

If exactly once semantics are enabled, the task will still be failed unconditionally.

Compatibility, Deprecation, and Migration Plan

Existing source connectors that do not set errors.tolerance to all will be unaffected. Default behavior is to still kill the task in the event of a producer write failure.

(Hypothetical use case): Existing source connectors that enable errors.tolerance all and expect to die on producer failure will need to update their connector to handle commitRecord with a null Metadata record. Not sure how much of these are in the wild, because it would require human intervention on the source system to fix whatever problem was causing the producer to die on kafka write in the first placeThe configuration item would default to false. Any Connect Worker that does not set it to true it will continue with the current behavior of killing the task on a Producer Exception.

Rejected Alternatives

Adding a new connect worker configuration item:

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