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https://issues.apache.org/jira/browse/KAFKA-7795?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16737496#comment-16737496
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ASF GitHub Bot commented on KAFKA-7795:
---------------------------------------
mumrah commented on pull request #6104: KAFKA-7795 Produce a ERROR log when
duplicate config keys are found
URL: https://github.com/apache/kafka/pull/6104
This change simply adds some formatted error logging if duplicate keys are
found when parsing a Kafka config file. Since we use Properties (which blindly
accepts duplicates), the validation must happen when the Properties instance is
loaded from a file.
No behavior changes here, just extra logging.
If I edit the broker config like:
```diff
diff --git a/config/server.properties b/config/server.properties
index 898d8ebc28..593651fd33 100644
--- a/config/server.properties
+++ b/config/server.properties
@@ -133,4 +133,8 @@ zookeeper.connection.timeout.ms=6000
# The default value for this is 3 seconds.
# We override this to 0 here as it makes for a better out-of-the-box
experience for development and testing.
# However, in production environments the default value of 3 seconds is
more suitable as this will help to avoid unnecessary, and potentially
expensive, rebalances during application startup.
-group.initial.rebalance.delay.ms=0
\ No newline at end of file
+group.initial.rebalance.delay.ms=0
+
+zookeeper.connection.timeout.ms=7000
+zookeeper.connection.timeout.ms=8000
```
It will produce the following error output at the top of the log:
```
[2019-01-08 15:25:44,892] INFO Registered kafka:type=kafka.Log4jController
MBean (kafka.utils.Log4jControllerRegistration$)
[2019-01-08 15:25:44,918] ERROR Duplicate config entries detected!
Ignoring zookeeper.connection.timeout.ms 6000
Ignoring zookeeper.connection.timeout.ms 7000
(org.apache.kafka.common.utils.Utils)
[2019-01-08 15:25:45,322] INFO starting (kafka.server.KafkaServer)
```
### Committer Checklist (excluded from commit message)
- [ ] Verify design and implementation
- [ ] Verify test coverage and CI build status
- [ ] Verify documentation (including upgrade notes)
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> Produce a warning when duplicate config keys are detected
> ---------------------------------------------------------
>
> Key: KAFKA-7795
> URL: https://issues.apache.org/jira/browse/KAFKA-7795
> Project: Kafka
> Issue Type: Improvement
> Components: config
> Reporter: David Arthur
> Priority: Minor
>
> It would be nice to perform some basic validation of the broker config
> so that things aren't unexpectedly overwritten.
> For example,
> {code:java}
> unclean.leader.election.enable=false
> // many other lines of config
> unclean.leader.election.enable=true
> {code}
> By detecting duplicate keys in the config file, we can inform users that
> there is a config problem.
> Note that this will not prevent the broker from starting, but rather it will
> produce some log warnings.
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