This page is meant as a template for writing a KIP. To create a KIP choose Tools->Copy on this page and modify with your content and replace the heading with the next KIP number and a description of your issue. Replace anything in italics with your own description.

Status

Current state: Under Discussion

Discussion thread: here [Change the link from the KIP proposal email archive to your own email thread]

JIRA: here 

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

Motivation

Currently, the consumer reports a metric of the lag between the high watermark of a log and the consumer offset. It will be useful to report a similar lead metric between the consumer offset and the start offset of the log. If this number gets close to 0, it's an indication that the consumer may stall or lose data soon. It would be useful to know per partition lead as well.

Public Interfaces

There is no programmatic public interface change. We are only adding new metrics.

Proposed Changes

Add min lead metric across all partitions to KafkaConsumer.the metric name would be:

"records-lead-min"

Also, add per partition lead metrics to KafkaConsumer. The metric names would be:

"TOPIC-PARTITION_ID.record-lead"
"TOPIC-PARTITION_ID.record-lead-avg"
"TOPIC-PARTITION_ID.record-lead-min"

The way to get the metrics is the same as getting other metrics. For example:

TopicPartition tp = new TopicPartition("topic", 0);
HashMap<String, String> tags = new HashMap<>();
tags.put("client-id", "metricTestConsumer0");

double currentLead = kafkaConsumer.metrics().get(new MetricName(tp + ".records-lead", "consumer-fetch-manager-metrics", "", tags)).value()
double averageLead = kafkaConsumer.metrics().get(new MetricName(tp + ".records-lead-avg", "consumer-fetch-manager-metrics", "", tags)).value()
double minLead = kafkaConsumer.metrics().get(new MetricName(tp + ".records-lead-min", "consumer-fetch-manager-metrics", "", tags)).value()

When the consumer does not own a partition anymore, the lead metric will be removed.

Compatibility, Deprecation, and Migration Plan

The change is fully backwards compatible.

Rejected Alternatives

None