GWphua opened a new pull request, #19518: URL: https://github.com/apache/druid/pull/19518
Partially addresses #19505 ### Description This PR changes `setProcessingThreadNames` from enabled-by-default to opt-in. `SpecificSegmentQueryRunner` currently renames the processing thread to `processing_<queryId>` around segment query execution, then restores the original thread name in a `finally` block. This is useful while inspecting thread dumps, but it also means every segment runner pays two `Thread.setName(...)` calls for each rename scope. #12514 added the `setProcessingThreadNames` query context after high-QPS testing showed that processing-thread renaming has measurable overhead for very quick segment scans. That PR kept renaming enabled by default, but allowed users to opt out by setting `setProcessingThreadNames=false`. After #15757, this previously small cost became more visible for realtime task queries with many hydrants, because non-bySegment realtime queries now wrap each hydrant with its own `SpecificSegmentQueryRunner`. What was once unnoticeable now becomes visible for realtime task queries with many small hydrants, where each hydrant is wrapped in a `SpecificSegmentQueryRunner` and the actual per-hydrant query work can be very small. ### Number of Thread Renames in the Peon The following table shows the number of thread renaming operations before and after #15757 |Hydrants param | Sinks | BEFORE | AFTER | |-- | -- | -- | -- | |50 | 1 | 4 | 204 | |100 | 1 | 4 | 404 | |200 | 1 | 4 | 804 | The benchmark parameter creates N persisted hydrants. The realtime sink also has the current incremental hydrant, so the query sees N + 1 hydrant references. Each `SpecificSegmentQueryRunner` has two rename scopes. Each scope calls `Thread.setName(...)` once to rename to `processing_<queryId>` and once to restore the original name. So each `SpecificSegmentQueryRunner` performs four `setName` calls. *This also shows that if there are any other additional performance overhead for query degradation beside thread renaming, the effects will be more pronounced for higher hydrant counts.* ### PR Fix This PR keeps the feature available by preserving the existing query context key `"setProcessingThreadNames"` but changes the default to false. ## Performance Benchmark Performance of queries for different versions: - Baseline: Before #15757 - BEFORE: Before this PR - AFTER: After this PR Lower ms/op is better. One JMH operation == one query execution. |Query type | Hydrants | Baseline ms/op | BEFORE ms/op | AFTER ms/op | Before v After | Baseline v After | |-- | -- | -- | -- | -- | -- | --| |timeseries | 10 | 0.064 | 0.231 | 0.141 | 39.0% faster | 121.8% slower| |timeseries | 50 | 0.186 | 1.036 | 0.588 | 43.2% faster | 216.2% slower| |timeseries | 100 | 0.335 | 1.879 | 1.113 | 40.8% faster | 232.7% slower| |timeseries | 200 | 0.625 | 3.923 | 2.290 | 41.6% faster | 266.4% slower| |segmentMetadata | 10 | 0.120 | 0.196 | 0.084 | 57.1% faster | 29.7% faster| |segmentMetadata | 50 | 0.287 | 0.807 | 0.323 | 59.9% faster | 12.8% slower| |segmentMetadata | 100 | 0.504 | 2.428 | 0.637 | 73.8% faster | 26.5% slower| |segmentMetadata | 200 | 1.960 | 3.393 | 1.615 | 52.4% faster | 17.6% faster| |scan | 10 | 0.057 | 0.159 | 0.064 | 59.5% faster | 12.0% slower| |scan | 50 | 0.186 | 0.751 | 0.281 | 62.6% faster | 50.6% slower| |scan | 100 | 0.377 | 1.638 | 0.571 | 65.1% faster | 51.7% slower| |scan | 200 | 0.800 | 3.732 | 1.365 | 63.4% faster | 70.6% slower| |groupBy | 10 | 4.366 | 0.233 | 0.135 | 42.0% faster | 96.9% faster| |groupBy | 50 | 21.671 | 0.820 | 0.456 | 44.4% faster | 97.9% faster| |groupBy | 100 | 37.954 | 1.707 | 0.881 | 48.4% faster | 97.7% faster| |groupBy | 200 | 76.499 | 3.720 | 2.085 | 43.9% faster | 97.3% faster| #### 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). --> Queries no longer rename processing threads by default. Users who rely on processing thread names in thread dumps can restore the old behavior per query by setting `setProcessingThreadNames=true`. <hr> ##### Key changed/added classes in this PR * `SpecificSegmentQueryRunner` * `SpecificSegmentQueryRunnerTest` * `query-context-reference.md` <hr> <!-- Check the items by putting "x" in the brackets for the done things. Not all of these items apply to every PR. Remove the items which are not done or not relevant to the PR. None of the items from the checklist below are strictly necessary, but it would be very helpful if you at least self-review the PR. --> This PR has: - [x] been self-reviewed. - [x] 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] a release note entry in the PR description. - [x] added Javadocs for most classes and all non-trivial methods. Linked related entities via Javadoc links. - [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. - [x] been tested in a test Druid cluster. -- This is an automated message from the Apache Git Service. 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