Kakfa retries Concept - What Basis retries will be stopped in Kafka? - apache-kafka

Question

As am new to Kafka , trying to understand the retries concept in Kafka . What basis retries process will be completed ?
Example Retries parameter we set as 7 . Now questions here ,
Kafka will be retried in all 7 times ?
Will be tried until successful process ? If so , How Kafka will come to know about successful ?
If that would be depends upon any parameter what Is that parameter and how ?

Answer 1

In distributed systems, retries are inevitable. From network errors to replication issues and even outages in downstream dependencies, services operating at a massive scale must be prepared to encounter, identify, and handle failure as gracefully as possible.
Kafka will retry until the initiated process is successfully completed or retry count is zero.
Kafka maintains the status of each API call ( producer , consumer, and Streams ), and if the error condition meets then retry count is decreased.
Please go through the completeBatch function of the Sender.java in the following URL to get more information.
https://github.com/apache/kafka/blob/68ac551966e2be5b13adb2f703a01211e6f7a34b/clients/src/main/java/org/apache/kafka/clients/producer/internals/Sender.java

Answer 2

I guess you are talking about producer retrying to send failed messages.
From kafka producer retries property documentation -
"Setting a value greater than zero will cause the client to resend any
record whose send fails with a potentially transient error."
This means that kafka producer will retry if the error it encountered is considered "Retriable". not all errors are retriable - for example, if the target kafka topic does not exist, theres no point in trying to send the message again.
but if for example the connection was interrupted, it makes sense to try again.
Important to note - retries are only relevant if you have set broker ack != 0.
So, in your example you have 7 retries configured.
I assume that ack is set to a value different than 0 because then no retries will be attempted.
If your message failed with a non-retriable error, Kafka producer will not try to send the message again (it will actually 'give-up' on that message and move on to next messages).
If your message failed with a retriable error, Kafka producer will retry sending until message is successfully sent, or until retries are exhausted (when 7 retries were attempted and none of them succeeded).
Kafka client producer knows when your message was successfully sent to broker because when ack is set to 1\all, the kafka broker is "Acknowledging" any message received and informs the producer (in a kind of handshake between the producer and broker).
see acks & retries # https://kafka.apache.org/documentation/#producerconfigs

Answer 3

Kafka reties happens for transient exceptions such as NotEnoughReplicaException.
In Kafka version <=2.0 default retry is 0.
In Kafka version > 2.0 default retry is Integer.MAX
From kafka 2.1 retries are bounded to timeouts, there are couple of producer configuration such as.
delivery.timeout.ms=120000ms - by default producer will retry for 2 mins, if retry is not successful after 2 mins the request will not send to broker and we have to handle manually.
retry.backoff.ms=100ms - by default every 100ms producer will retry till delivery.timeout reaches.