Kafka: Continuously getting FETCH_SESSION_ID_NOT_FOUND

Question

I am continuously getting FETCH_SESSION_ID_NOT_FOUND. I'm not sure why its happening. Can anyone please me here what is the problem and what will be the impact on consumers and brokers.

Kafka Server Log:

INFO [2019-10-18 12:09:00,709] [ReplicaFetcherThread-1-8][] org.apache.kafka.clients.FetchSessionHandler - [ReplicaFetcher replicaId=6, leaderId=8, fetcherId=1] Node 8 was unable to process the fetch request with (sessionId=258818904, epoch=2233): FETCH_SESSION_ID_NOT_FOUND.
 INFO [2019-10-18 12:09:01,078] [ReplicaFetcherThread-44-10][] org.apache.kafka.clients.FetchSessionHandler - [ReplicaFetcher replicaId=6, leaderId=10, fetcherId=44] Node 10 was unable to process the fetch request with (sessionId=518415741, epoch=4416): FETCH_SESSION_ID_NOT_FOUND.
 INFO [2019-10-18 12:09:01,890] [ReplicaFetcherThread-32-9][] org.apache.kafka.clients.FetchSessionHandler - [ReplicaFetcher replicaId=6, leaderId=9, fetcherId=32] Node 9 was unable to process the fetch request with (sessionId=418200413, epoch=3634): FETCH_SESSION_ID_NOT_FOUND.

Kafka Consumer Log:

12:29:58,936 INFO  [FetchSessionHandler:383] [Consumer clientId=bannerGroupMap#87e2af7cf742#test, groupId=bannerGroupMap#87e2af7cf742#test] Node 8 was unable to process the fetch request with (sessionId=1368981303, epoch=60): FETCH_SESSION_ID_NOT_FOUND.
12:29:58,937 INFO  [FetchSessionHandler:383] [Consumer clientId=bannerGroupMap#87e2af7cf742#test, groupId=bannerGroupMap#87e2af7cf742#test] Node 3 was unable to process the fetch request with (sessionId=1521862194, epoch=59): FETCH_SESSION_ID_NOT_FOUND.
12:29:59,939 INFO  [FetchSessionHandler:383] [Consumer clientId=zoneGroupMap#87e2af7cf742#test, groupId=zoneGroupMap#87e2af7cf742#test] Node 7 was unable to process the fetch request with (sessionId=868804875, epoch=58): FETCH_SESSION_ID_NOT_FOUND.
12:30:06,952 INFO  [FetchSessionHandler:383] [Consumer clientId=creativeMap#87e2af7cf742#test, groupId=creativeMap#87e2af7cf742#test] Node 3 was unable to process the fetch request with (sessionId=1135396084, epoch=58): FETCH_SESSION_ID_NOT_FOUND.
12:30:12,965 INFO  [FetchSessionHandler:383] [Consumer clientId=creativeMap#87e2af7cf742#test, groupId=creativeMap#87e2af7cf742#test] Node 6 was unable to process the fetch request with (sessionId=1346340004, epoch=56): FETCH_SESSION_ID_NOT_FOUND.

Cluster Details:

Broker: 13 (1 Broker : 14 cores & 36GB memory)
Kafka cluster version: 2.0.0
Kafka Java client version: 2.0.0
Number topics: ~15. 
Number of consumers: 7K (all independent and manually assigned all partitions of a topic to a consumers. One consumer is consuming all partitions from a topic only) 

Answer 1

Increase the value of max.incremental.fetch.session.cache.slots. The default value is 1K, in my case I have increased it to 10K and it fixed.

Answer 2

This is not an error, it's INFO and it's telling you that you are connected but it can't fetch a session id because there's none to fetch.

It's normal to see this message and the flushing message in the log.

Answer 3

I have increased it at first from 1K to 2K, and in the second step from 2K to 4K, and as long as the limit was not exhausted, there was no appearance of error:

As it seemed to me like a session leak by certain unidentified consumer, I didn't try 10K limit yet, but reading Hrishikesh Mishra's answer, I definitely will. Because, increasing the limit also decreased the frequency of error, so the question of identifying individual consumer groups that are opening excessive number of incremental fetch sessions, mentioned here How to check the actual number of incremental fetch session cache slots used in Kafka cluster? , may be irrelevant in the end.