Set an upper bound for the number of timeline events gathered

[szegedi]

What does this PR do?

Establishes an upper limit on the number of non-CPU timeline events that can be gathered within a single upload period.

Motivation

It's a bad idea for it to be unbounded.

Additional Notes

The upper limit is rather conservative and is heuristically derived from the CPU sampling rate, the upload period, and the number of libuv worker threads (and available parallelism.) E.g. if the CPU sampling rate is 10ms and we upload every 60s, that means at most 6000 CPU samples. We'd like to be able to observe oversubscription on the libuv thread pool. If there are 4 libuv threads, we'd like to be able to observe at least 6000*5 events (events executing on at least 4 threads + 1 waiting for detecting oversubscription). Finally, another 6000 events are allowed for GC events so that gives us uploadPeriod / samplingPeriod * (threads + 2)) as the maximum number of events we wish to sample. With our defaults of 65s upload period, 99Hz sampling rate, and 4 libuv threads we'll collect at most 38613 events (when more are gathered, events get randomly discarded.) Because we already employ sampling I believe this upper bound is not very limiting in ordinary usage – its purpose is to prevent pathological memory usage runoff.

Jira: PROF-12127

[codecov]

Codecov Report

Attention: Patch coverage is 63.15789% with 21 lines in your changes missing coverage. Please review.

Project coverage is 81.28%. Comparing base (195f0ce) to head (b1b5bd6).

Files with missing lines	Patch %	Lines
...ackages/dd-trace/src/profiling/profilers/events.js	43.24%	21 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6089      +/-   ##
==========================================
- Coverage   81.94%   81.28%   -0.67%     
==========================================
  Files         473      468       -5     
  Lines       19560    19482      -78     
==========================================
- Hits        16029    15835     -194     
- Misses       3531     3647     +116     

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[github-actions]

Overall package size

Self size: 9.68 MB
Deduped: 109.26 MB
No deduping: 109.65 MB

Dependency sizes

| name | version | self size | total size | |------|---------|-----------|------------| | @datadog/libdatadog | 0.7.0 | 35.02 MB | 35.02 MB | | @datadog/native-appsec | 10.0.0 | 20.3 MB | 20.31 MB | | @datadog/native-iast-taint-tracking | 4.0.0 | 11.72 MB | 11.73 MB | | @datadog/pprof | 5.9.0 | 9.77 MB | 10.14 MB | | @opentelemetry/core | 1.30.1 | 908.66 kB | 7.16 MB | | protobufjs | 7.5.3 | 2.95 MB | 5.6 MB | | @datadog/wasm-js-rewriter | 4.0.1 | 2.85 MB | 3.58 MB | | @datadog/native-metrics | 3.1.1 | 1.02 MB | 1.43 MB | | @opentelemetry/api | 1.8.0 | 1.21 MB | 1.21 MB | | jsonpath-plus | 10.3.0 | 617.18 kB | 1.08 MB | | import-in-the-middle | 1.14.2 | 122.36 kB | 850.93 kB | | lru-cache | 10.4.3 | 804.3 kB | 804.3 kB | | source-map | 0.7.4 | 226 kB | 226 kB | | opentracing | 0.14.7 | 194.81 kB | 194.81 kB | | pprof-format | 2.1.0 | 111.69 kB | 111.69 kB | | @datadog/sketches-js | 2.1.1 | 109.9 kB | 109.9 kB | | lodash.sortby | 4.7.0 | 75.76 kB | 75.76 kB | | ignore | 7.0.5 | 63.38 kB | 63.38 kB | | istanbul-lib-coverage | 3.2.2 | 34.37 kB | 34.37 kB | | rfdc | 1.4.1 | 27.15 kB | 27.15 kB | | @isaacs/ttlcache | 1.4.1 | 25.2 kB | 25.2 kB | | dc-polyfill | 0.1.9 | 25.11 kB | 25.11 kB | | tlhunter-sorted-set | 0.1.0 | 24.94 kB | 24.94 kB | | shell-quote | 1.8.3 | 23.74 kB | 23.74 kB | | limiter | 1.1.5 | 23.17 kB | 23.17 kB | | retry | 0.13.1 | 18.85 kB | 18.85 kB | | semifies | 1.0.0 | 15.84 kB | 15.84 kB | | jest-docblock | 29.7.0 | 8.99 kB | 12.76 kB | | crypto-randomuuid | 1.0.0 | 11.18 kB | 11.18 kB | | ttl-set | 1.0.0 | 4.61 kB | 9.69 kB | | mutexify | 1.4.0 | 5.71 kB | 8.74 kB | | path-to-regexp | 0.1.12 | 6.6 kB | 6.6 kB | | koalas | 1.0.2 | 6.47 kB | 6.47 kB | | module-details-from-path | 1.0.4 | 3.96 kB | 3.96 kB |

_{🤖 This report was automatically generated by heaviest-objects-in-the-universe}

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-07-15 08:17:48

Comparing candidate commit b1b5bd6 in PR branch szegedi/timeline-event-max with baseline commit 195f0ce in branch master.

Found 0 performance improvements and 0 performance regressions! Performance is the same for 1273 metrics, 50 unstable metrics.