jasonk000 opened a new pull request #12102:
URL: https://github.com/apache/druid/pull/12102
### Description
Introduce a back-off to the `HttpPostEmitter` `send()` thread loop to
minimise the amount of log spamming and CPU.
Fixes #11279.
#### Introduce HttpPostEmitterLoggerStressTest
Introduce a test to count how many logged events are triggered during a loop
scenario. It confirms that no more than some maximum send timeout log events
are written in duration of the test. Test runs typically for 6 seconds, and
expects limit of 1000 send attempts in that 6 second period.
Currently, the HttpPostEmitter thread submits 150K events in the test window.
```
[ERROR] Failures:
[ERROR]
org.apache.druid.java.util.emitter.core.HttpPostEmitterLoggerStressTest.testBurstFollowedByQuietPeriod(org.apache.druid.java.util.emitter.core.HttpPostEmitterLoggerStressTest)
[ERROR] Run 1:
HttpPostEmitterLoggerStressTest.testBurstFollowedByQuietPeriod:98 too many
timeouts (159620), expect less than (1000)
[ERROR] Run 2:
HttpPostEmitterLoggerStressTest.testBurstFollowedByQuietPeriod:98 too many
timeouts (166201), expect less than (1000)
[ERROR] Run 3:
HttpPostEmitterLoggerStressTest.testBurstFollowedByQuietPeriod:98 too many
timeouts (173177), expect less than (1000)
[ERROR] Run 4:
HttpPostEmitterLoggerStressTest.testBurstFollowedByQuietPeriod:98 too many
timeouts (175135), expect less than (1000)
```
#### Introduce a backoff to the send() loop when the specific timeout is
experienced.
A simple backoff is chosen at 1/5th the minimum time.
An alternative solution which might be better involves a larger rewrite of
this class, as the class currently splits responsibilities for managing the
batching and sending across multiple classes and threads. A simpler codebase
might run a simpler submission loop with a more explicit throttle and batching
mechanism instead of the current batching handoffs.
This PR has:
- [x] been self-reviewed.
- [ ] N/A 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.)
- [x] added documentation for new or modified features or behaviors.
- [x] added Javadocs for most classes and all non-trivial methods. Linked
related entities via Javadoc links.
- [ ] N/A added or updated version, license, or notice information in
[licenses.yaml](https://github.com/apache/druid/blob/master/dev/license.md)
- [x] added comments explaining the "why" and the intent of the code
wherever would not be obvious for an unfamiliar reader.
- [x] 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.
- [ ] N/A added integration tests.
- [ ] been tested in a test Druid cluster.
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