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Status

Current state:  Under Discussion

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]
https://www.mail-archive.com/dev@kafka.apache.org/msg100621.html

Voting Thread: https://www.mail-archive.com/dev@kafka.apache.org/msg100812.html

JIRA:  JIRA: JiraserverASF JIRAserverId5aa69414-a9e9-3523-82ec-879b028fb15bkeyKAFKA-8830

Please keep the discussion on the mailing list rather than commenting on the wiki (wiki discussions get unwieldy fast).

Motivation

This KIP tries to address the following issues in Kafka.

As part of KIP-82, the headers are added to Kafka ProducerRecord and ConsumerRecord.As discussed in that KIP the headers provide lot of benefits especially metadata association with the record and propagating same along with record. These headers are very helpful to pass client metadata and unique Id for the record.

Currently the Once the record is sent i.e added to ProduceBatch, we get RecordMetaData along with callback to track. The RecordMetadata contains details like topic, partition, offset, timestamp etc. But there is no link information on for which record this RecordMetadata belongs to.

For example in ProducerInterceptor we have an interface method onAcknowledgement(...) which is used to intercept the status of the record produced to kafka. It has  RecordMetadata as parameter. Since RecordMetaData doesn't contain headers information we have no insights on  for which record this RecordMetadata belongs to. Record headers will have record metadata like unique Id from client for each record.

If we add record headers to RecordMetaData, we can link record to metadata status i.e we can track what is the produce status and metadata for the given record.

Public Interfaces

Proposed Changes

Describe the new thing you want to do in appropriate detail. This may be fairly extensive and have large subsections of its own. Or it may be a few sentences. Use judgement based on the scope of the change.

. Having headers information as part of RecordMetaData will bridge this gap.

It will make the  context of the record available to Interceptors and open up possibility for building more features.

Example: 

As the Kafka usage is growing, we see Kafka being used for Payment transactional, Settlement  and reconciliation use cases. These kind of use cases are very sensitive to message loss.Current dataloss auditing systems like chaperone uses time window based aggregations, which is not sufficient when we need message level traceability. In order to build message level traceability, we need the capability to track message production and consumption.If we choose to track message production status based on acknowledgment the producer receives, we will need ability to relate acknowledgment to the record. Having this ability in Interceptors can help us to link the record to its acknowledgement. 

Public Interfaces

We will change Changes to RecordMetaData and FutureRecordMetaData to have headers information along with other metadata like topic, partition and offset etc..

Proposed Changes

1. Changes to RecordMetaData

   Code Block
   language java title RecordMetaData.java
   public final class RecordMetadata { /** * Partition value for record without partition assigned */ public static final int UNKNOWN_PARTITION = -1; private final long offset; .......... private final TopicPartition topicPartition; private final Header[] headers; private volatile Long checksum; public RecordMetadata(TopicPartition topicPartition, long baseOffset, long relativeOffset, long timestamp, Long checksum, int serializedKeySize, int serializedValueSize, Header[] headers) { // ignore the relativeOffset if the base offset is -1, // since this indicates the offset is unknown this.offset = baseOffset == -1 ? baseOffset : baseOffset + relativeOffset; this.timestamp = timestamp; this.checksum = checksum; this.serializedKeySize = serializedKeySize; this.serializedValueSize = serializedValueSize; this.topicPartition = topicPartition; this.headers = headers; } ...... /** * The headers of the record was sent to */ public Header[] headers() { return this.headers; } ...... }

   
   

2. Changes to FutureRecordMetaData

   Code Block
   language java title FutureRecordMetaData.java
   public final class FutureRecordMetadata implements Future<RecordMetadata> { private final ProduceRequestResult result; .......... private final Header[] headers; private volatile FutureRecordMetadata nextRecordMetadata = null; public FutureRecordMetadata(ProduceRequestResult result, long relativeOffset, long createTimestamp, Long checksum, int serializedKeySize, int serializedValueSize, Time time, Header[] headers) { this.result = result; this.relativeOffset = relativeOffset; this.createTimestamp = createTimestamp; this.checksum = checksum; this.serializedKeySize = serializedKeySize; this.serializedValueSize = serializedValueSize; this.time = time; this.headers = headers; } ....... }

...

1. 
   

2. In ProduceBatch add headers to

...

1. FutureRecordMetaData while appending record to the batch.

...

1. Code Block
   language java title ProducerBatch.java
   public FutureRecordMetadata tryAppend(long timestamp, byte[] key, byte[] value, Header[] headers, Callback callback, long now) { ....... ......... FutureRecordMetadata future = new FutureRecordMetadata(this.produceFuture, this.recordCount, timestamp, checksum, key == null ? -1 : key.length, value == null ? -1 : value.length, Time.SYSTEM, headers); // we have to keep every future returned to the users in case the batch needs to be // split to several new batches and resent. thunks.add(new Thunk(callback, future)); this.recordCount++; return future; } }

            

2. Add headers to RecordMetaData for send error scenarios also.

Compatibility, Deprecation, and Migration Plan

...

• What impact (if any) will there be on existing users?

                 There is no impact. Since we are passing same reference to the headers there is no memory impact.

• If we are changing behavior how will we phase out the older behavior?

...

• When will we remove the existing behavior?

               We will keep the existing behavior   Not applicable.

Rejected Alternatives

...

1.  Producer callback provides a way to link record to its RecordMetaData.

           In this case the context linking  on client side and  depends on client implementation  where as  interceptors having similar RecordMetaData but no access to headers onAcknowledgement(...).

producer.send(message, (RecordMetadata metadata, Exception exception) -> {
                if (metadata!=null && exception == null) {
                
                    String topic = metadata.topic();
                    
                    Iterator<Header> it = message.headers().iterator();

                   .....
                }
            });