suneet-s opened a new pull request, #14121:
URL: https://github.com/apache/druid/pull/14121
### Description
This change makes the events emitted by the logging emitter more useful by
logging them with the feed of the event as a
log4j Marker.
This PR updates Druid's `Logger` interface to include functions that allows
developers to mark log messages with a Marker, and then makes use of them in
the `LoggingEmitter`.
The output from the logging emitter with the default Druid configuration
will now look like
```
2023-04-19T23:54:51,121 INFO [qtp52562984-77]
org.apache.druid.java.util.emitter.core.LoggingEmitter - [request_logs]
{"feed":"request_logs","service":"druid/router","query":null,"host":"localhost:8888","sql":"SELECT
1337","queryStats":{"query/time":537,"success":true},"remoteAddr":"[0:0:0:0:0:0:0:1]","sqlQueryContext":{"timeout":15000,"sqlQueryId":"241a044f-da54-446d-8c16-6b62cace3247","queryId":"241a044f-da54-446d-8c16-6b62cace3247"},"timestamp":"2023-04-19T23:54:51.118Z"}
2023-04-19T23:49:13,336 INFO [MonitorScheduler-0]
org.apache.druid.java.util.emitter.core.LoggingEmitter - [metrics]
{"feed":"metrics","metric":"jetty/threadPool/busy","service":"druid/router","host":"localhost:8888","version":"27.0.0-SNAPSHOT","value":4,"timestamp":"2023-04-19T23:49:13.336Z"}
```
Druid operators can now configure their log4j config to route the logs
emitted to different locations based on their use. For example, an operator
might want to configure different feeds to be written to different files. They
can now do this with config that looks like
In Druid common.runtime.properties
```
druid.emitter=logging
druid.emitter.logging.logLevel=info
# configure request logging via the emitter
druid.request.logging.type=emitter
druid.request.logging.feed=request_logs
```
Then update the log4j.xml (by default in `_common/log4j2.xml`) with a new
appender and route the logs based on their feeds
```
<Appenders>
... // Other appender configs
<File name="emitterAppender"
fileName="/logs/druid/emitter/%markerSimpleName.log">
<PatternLayout pattern="%d{ISO8601} - %m%n"/>
</File>
</Appenders>
<Loggers>
... // Other Logger configs
<Logger name="org.apache.druid.java.util.emitter.core.LoggingEmitter"
level="info" additivity="false">
<Appender-ref ref="emitterAppender"/>
</Logger>
</Loggers>
```
#### Release note
<!-- Give your best effort to summarize your changes in a couple of
sentences aimed toward Druid users.
If your change doesn't have end user impact, you can skip this section.
For tips about how to write a good release note, see [Release
notes](https://github.com/apache/druid/blob/master/CONTRIBUTING.md#release-notes).
-->
<hr>
##### Key changed/added classes in this PR
* `*/log4j2.xml` - This changes the default log4j config to add Markers to
be included in the log if it is specified in the code.
*
`processing/src/main/java/org/apache/druid/java/util/common/logger/Logger.java`
<hr>
This PR has:
- [ ] been self-reviewed.
- [ ] using the [concurrency
checklist](https://github.com/apache/druid/blob/master/dev/code-review/concurrency.md)
(Remove this item if the PR doesn't have any relation to concurrency.)
- [ ] added documentation for new or modified features or behaviors.
- [ ] a release note entry in the PR description.
- [ ] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [ ] added or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [ ] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [ ] added unit tests or modified existing tests to cover new code paths,
ensuring the threshold for [code
coverage](https://github.com/apache/druid/blob/master/dev/code-review/code-coverage.md)
is met.
- [ ] added integration tests.
- [x] been tested in a test Druid cluster.
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