[FLINK-10874][kafka-docs] Document likely cause of UnknownTopicOrPart…

…itionException

docs/dev/connectors/kafka.md

@@ -660,19 +660,6 @@ we recommend setting the number of retries to a higher value.
 **Note**: There is currently no transactional producer for Kafka, so Flink can not guarantee exactly-once delivery
 into a Kafka topic.
 
-<div class="alert alert-warning">
- <strong>Attention:</strong> Depending on your Kafka configuration, even after Kafka acknowledges
- writes you can still experience data loss. In particular keep in mind the following Kafka settings:
- <ul>
- <li><tt>acks</tt></li>
- <li><tt>log.flush.interval.messages</tt></li>
- <li><tt>log.flush.interval.ms</tt></li>
- <li><tt>log.flush.*</tt></li>
- </ul>
- Default values for the above options can easily lead to data loss. Please refer to Kafka documentation
- for more explanation.
-</div>
-
 #### Kafka 0.11 and newer
 
 With Flink's checkpointing enabled, the `FlinkKafkaProducer011` (`FlinkKafkaProducer` for Kafka >= 1.0.0 versions) can provide
@@ -690,21 +677,6 @@ chosen by passing appropriate `semantic` parameter to the `FlinkKafkaProducer011
  or `read_uncommitted` - the latter one is the default value) for any application consuming records
  from Kafka.
 
-<div class="alert alert-warning">
- <strong>Attention:</strong> Depending on your Kafka configuration, even after Kafka acknowledges
- writes you can still experience data losses. In particular keep in mind about following properties
- in Kafka config:
- <ul>
- <li><tt>acks</tt></li>
- <li><tt>log.flush.interval.messages</tt></li>
- <li><tt>log.flush.interval.ms</tt></li>
- <li><tt>log.flush.*</tt></li>
- </ul>
- Default values for the above options can easily lead to data loss. Please refer to the Kafka documentation
- for more explanation.
-</div>
-
-
 ##### Caveats
 
 `Semantic.EXACTLY_ONCE` mode relies on the ability to commit transactions
@@ -831,4 +803,38 @@ A mismatch in service name between client and server configuration will cause th
 For more information on Flink configuration for Kerberos security, please see [here]({{ site.baseurl}}/ops/config.html).
 You can also find [here]({{ site.baseurl}}/ops/security-kerberos.html) further details on how Flink internally setups Kerberos-based security.
 
+## Troubleshooting
+
+<div class="alert alert-warning">
+If you have a problem with Kafka when using Flink, keep in mind that Flink only wraps
+<a href="https://kafka.apache.org/documentation/#consumerapi">KafkaConsumer</a> or
+<a href="https://kafka.apache.org/documentation/#producerapi">KafkaProducer</a>
+and your problem might be independent of Flink and sometimes can be solved by upgrading Kafka brokers,
+reconfiguring Kafka brokers or reconfiguring <tt>KafkaConsumer</tt> or <tt>KafkaProducer</tt> in Flink.
+Some examples of common problems are listed below.
+</div>
+
+### Data loss
+
+Depending on your Kafka configuration, even after Kafka acknowledges
+writes you can still experience data loss. In particular keep in mind about the following properties
+in Kafka config:
+
+- `acks`
+- `log.flush.interval.messages`
+- `log.flush.interval.ms`
+- `log.flush.*`
+
+Default values for the above options can easily lead to data loss.
+Please refer to the Kafka documentation for more explanation.
+
+### UnknownTopicOrPartitionException
+
+One possible cause of this error is when a new leader election is taking place,
+for example after or during restarting a Kafka broker.
+This is a retriable exception, so Flink job should be able to restart and resume normal operation.
+It also can be circumvented by changing `retries` property in the producer settings.
+However this might cause reordering of messages,
+which in turn if undesired can be circumvented by setting `max.in.flight.requests.per.connection` to 1.
+
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