perf(trace): encode agentless IDs without formatting by BridgeAR · Pull Request #2452 · DataDog/libdatadog

BridgeAR · 2026-09-03T11:21:55Z

What does this PR do?

Replaces formatting-backed agentless trace, span, parent, and link ID serialization with fixed-width lowercase hexadecimal buffers. Exact wire tests and lasting Criterion workloads cover common HTTP and span-link traces.

Motivation

Formatting allocated temporary strings for every serialized ID in the agentless hot path.

Additional Notes

With production-deduplicated spans, position-balanced Criterion runs improved common HTTP traces by 32.35% and span-link traces by 44.48% on macOS arm64.

How to test the change?

Run cargo test -p libdd-trace-utils --lib agentless_encoder and cargo bench -p libdd-trace-utils --bench main -- agentless_encoding.

Replace formatting allocations with fixed-width stack buffers for agentless trace, span, parent, and link IDs. With production-deduplicated spans, position-balanced Criterion runs on macOS arm64 improved common HTTP traces by 32.35% and span-link traces by 44.48%.

github-actions · 2026-09-03T11:23:55Z

📚 Documentation Check Results

⚠️ 765 documentation warning(s) found

📦 `libdd-trace-utils` - 765 warning(s)

Updated: 2026-09-03 11:23:54 UTC | Commit: 68c1ed5 | missing-docs job results

github-actions · 2026-09-03T11:25:45Z

🔒 Cargo Deny Results

⚠️ 3 issue(s) found, showing only errors (advisories, bans, sources)

📦 `libdd-trace-utils` - 3 error(s)

Show output

error[vulnerability]: Invalid pointer dereference in `fmt::Pointer` impl for `Atomic` and `Shared` when the underlying pointer is invalid
   ┌─ /home/runner/work/libdatadog/libdatadog/Cargo.lock:63:1
   │
63 │ crossbeam-epoch 0.9.18 registry+https://github.com/rust-lang/crates.io-index
   │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ security vulnerability detected
   │
   ├ ID: RUSTSEC-2026-0204
   ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2026-0204
   ├ Affected versions of `fmt::Display` dereference the underlying pointer. This causes a invalid pointer dereference e.g., when a pointer created with `Atomic::null` or `Shared::null`. `fmt::Debug` impls and pre-0.9 `fmt::Display` impls, which do not dereference pointers, are not affected by this issue.
   ├ Announcement: https://github.com/crossbeam-rs/crossbeam/pull/1276
   ├ Solution: Upgrade to >=0.9.20 (try `cargo update -p crossbeam-epoch`)
   ├ crossbeam-epoch v0.9.18
     └── crossbeam-deque v0.8.5
         └── rayon-core v1.12.1
             └── rayon v1.10.0
                 └── criterion v0.5.1
                     ├── libdd-common v5.2.0
                     │   ├── libdd-capabilities-impl v4.0.0
                     │   │   └── libdd-trace-utils v11.0.0
                     │   │       └── (dev) libdd-trace-utils v11.0.0 (*)
                     │   └── libdd-trace-utils v11.0.0 (*)
                     ├── (dev) libdd-trace-normalization v4.0.0
                     │   └── libdd-trace-utils v11.0.0 (*)
                     └── (dev) libdd-trace-utils v11.0.0 (*)

error[vulnerability]: h2 unbounded empty DATA frames
   ┌─ /home/runner/work/libdatadog/libdatadog/Cargo.lock:97:1
   │
97 │ h2 0.4.6 registry+https://github.com/rust-lang/crates.io-index
   │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ security vulnerability detected
   │
   ├ ID: RUSTSEC-2026-0258
   ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2026-0258
   ├ The h2 crate, used internally by hyper, had a flaw that would accept and queue empty DATA frames without limit.
     If streams were not actively drained, this could lead to unbounded memory usage, or a panic if the length overflows.
     
     Low severity.
     
     Patched in v0.4.16.
   ├ Announcement: https://github.com/hyperium/hyper/security/advisories/GHSA-q83h-524g-xf6h
   ├ Solution: Upgrade to >=0.4.16 (try `cargo update -p h2`)
   ├ h2 v0.4.6
     └── hyper v1.6.0
         ├── httpmock v0.8.0-alpha.1
         │   └── libdd-trace-utils v11.0.0
         │       └── (dev) libdd-trace-utils v11.0.0 (*)
         ├── hyper-rustls v0.27.7
         │   └── libdd-common v5.2.0
         │       ├── libdd-capabilities-impl v4.0.0
         │       │   └── libdd-trace-utils v11.0.0 (*)
         │       └── libdd-trace-utils v11.0.0 (*)
         ├── hyper-util v0.1.17
         │   ├── httpmock v0.8.0-alpha.1 (*)
         │   ├── hyper-rustls v0.27.7 (*)
         │   └── libdd-common v5.2.0 (*)
         ├── libdd-common v5.2.0 (*)
         └── libdd-trace-utils v11.0.0 (*)

error[unsound]: Rand is unsound with a custom logger using `rand::rng()`
    ┌─ /home/runner/work/libdatadog/libdatadog/Cargo.lock:184:1
    │
184 │ rand 0.8.5 registry+https://github.com/rust-lang/crates.io-index
    │ ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ unsound advisory detected
    │
    ├ ID: RUSTSEC-2026-0097
    ├ Advisory: https://rustsec.org/advisories/RUSTSEC-2026-0097
    ├ It has been reported (by [@lopopolo](https://github.com/lopopolo)) that the `rand` library is [unsound](https://rust-lang.github.io/unsafe-code-guidelines/glossary.html#soundness-of-code--of-a-library) (i.e. that safe code using the public API can cause Undefined Behaviour) when all the following conditions are met:
      
      - The `log` and `thread_rng` features are enabled
      - A [custom logger](https://docs.rs/log/latest/log/#implementing-a-logger) is defined
      - The custom logger accesses `rand::rng()` (previously `rand::thread_rng()`) and calls any `TryRng` (previously `RngCore`) methods on `ThreadRng`
      - The `ThreadRng` (attempts to) reseed while called from the custom logger (this happens every 64 kB of generated data)
      - Trace-level logging is enabled or warn-level logging is enabled and the random source (the `getrandom` crate) is unable to provide a new seed
      
      `TryRng` (previously `RngCore`) methods for `ThreadRng` use `unsafe` code to cast `*mut BlockRng<ReseedingCore>` to `&mut BlockRng<ReseedingCore>`. When all the above conditions are met this results in an aliased mutable reference, violating the Stacked Borrows rules. Miri is able to detect this violation in sample code. Since construction of [aliased mutable references is Undefined Behaviour](https://doc.rust-lang.org/stable/nomicon/references.html), the behaviour of optimized builds is hard to predict.
    ├ Announcement: https://github.com/rust-random/rand/pull/1763
    ├ Solution: Upgrade to >=0.10.1 OR <0.10.0, >=0.9.3 OR <0.9.0, >=0.8.6 (try `cargo update -p rand`)
    ├ rand v0.8.5
      ├── (dev) libdd-common v5.2.0
      │   ├── libdd-capabilities-impl v4.0.0
      │   │   └── libdd-trace-utils v11.0.0
      │   │       └── (dev) libdd-trace-utils v11.0.0 (*)
      │   └── libdd-trace-utils v11.0.0 (*)
      ├── (dev) libdd-trace-normalization v4.0.0
      │   └── libdd-trace-utils v11.0.0 (*)
      ├── libdd-trace-utils v11.0.0 (*)
      └── proptest v1.5.0
          ├── (dev) libdd-common v5.2.0 (*)
          └── (dev) libdd-tinybytes v1.1.2
              ├── (dev) libdd-tinybytes v1.1.2 (*)
              └── libdd-trace-utils v11.0.0 (*)

advisories FAILED, bans ok, sources ok

Updated: 2026-09-03 11:25:44 UTC | Commit: 68c1ed5 | dependency-check job results

datadog-prod-us1-5 · 2026-09-03T11:31:44Z

✅ All CI checks and tests passed.

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 100.00%
• Overall Coverage: 77.05% (-0.04%)

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: f194c4f | Docs | View more details | Give us feedback!}

pr-commenter · 2026-09-03T11:55:02Z

Benchmarks

Comparison

Benchmark execution time: 2026-09-03 11:53:37

Comparing candidate commit f194c4f in PR branch BridgeAR/2026-09-03-agentless-hex-ids with baseline commit efbbf4c in branch main.

Found 1 performance improvements and 2 performance regressions! Performance is the same for 138 metrics, 0 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

🟩 = significantly better candidate vs. baseline
🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:otlp/e2e_json/1x1000

🟥 execution_time [+330.923µs; +336.709µs] or [+8.170%; +8.313%]

scenario:otlp/encode_json/1x1000

🟥 execution_time [+348.118µs; +349.111µs] or [+20.488%; +20.547%]

scenario:vec_map/as_deduped_map/needs_dedup_1_in_4/8

🟩 execution_time [-17.203ns; -16.918ns] or [-4.179%; -4.110%]

Benchmark execution time: 2026-09-03 11:51:18

Comparing candidate commit f194c4f in PR branch BridgeAR/2026-09-03-agentless-hex-ids with baseline commit efbbf4c in branch main.

Found 1 performance improvements and 1 performance regressions! Performance is the same for 73 metrics, 10 unstable metrics.

Explanation

This is an A/B test comparing a candidate commit's performance against that of a baseline commit. Performance changes are noted in the tables below as:

🟩 = significantly better candidate vs. baseline
🟥 = significantly worse candidate vs. baseline

We compute a confidence interval (CI) over the relative difference of means between metrics from the candidate and baseline commits, considering the baseline as the reference.

If the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD), the change is considered significant.

Feel free to reach out to #apm-benchmarking-platform on Slack if you have any questions.

More details about the CI and significant changes

You can imagine this CI as a range of values that is likely to contain the true difference of means between the candidate and baseline commits.

CIs of the difference of means are often centered around 0%, because often changes are not that big:

---------------------------------(------|---^--------)-------------------------------->
                              -0.6%    0%  0.3%     +1.2%
                                 |          |        |
         lower bound of the CI --'          |        |
sample mean (center of the CI) -------------'        |
         upper bound of the CI ----------------------'

As described above, a change is considered significant if the CI is entirely outside the configured SIGNIFICANT_IMPACT_THRESHOLD (or the deprecated UNCONFIDENCE_THRESHOLD).

For instance, for an execution time metric, this confidence interval indicates a significantly worse performance:

----------------------------------------|---------|---(---------^---------)---------->
                                       0%        1%  1.3%      2.2%      3.1%
                                                  |   |         |         |
       significant impact threshold --------------'   |         |         |
                      lower bound of CI --------------'         |         |
       sample mean (center of the CI) --------------------------'         |
                      upper bound of CI ----------------------------------'

scenario:datadog_sample_span/multiple_rules_last_match/wall_time

🟩 execution_time [-9.214ns; -9.060ns] or [-4.457%; -4.382%]

scenario:glob_matcher/unicode_pattern_wildcard_match/wall_time

🟥 execution_time [+5.653ns; +5.733ns] or [+4.563%; +4.627%]

Candidate

Omitted due to size.

Baseline

Omitted due to size.

dd-octo-sts · 2026-09-03T11:59:04Z

Artifact Size Benchmark Report

aarch64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.a	91.30 MB	91.28 MB	--.02% (-21.16 KB) 💪
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.so	8.45 MB	8.45 MB	0% (0 B) 👌

aarch64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.so	11.38 MB	11.38 MB	--.01% (-1.37 KB) 💪
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.a	102.61 MB	102.59 MB	--.02% (-22.19 KB) 💪

libdatadog-x64-windows

Artifact	Baseline	Commit	Change
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.dll	27.33 MB	27.33 MB	--.01% (-3.50 KB) 💪
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.lib	96.08 KB	96.08 KB	0% (0 B) 👌
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.pdb	185.41 MB	185.40 MB	-0% (-8.00 KB) 👌
/libdatadog-x64-windows/debug/static/datadog_profiling_ffi.lib	805.24 MB	804.83 MB	--.05% (-418.44 KB) 💪
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.dll	9.01 MB	9.01 MB	--.03% (-3.00 KB) 💪
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.lib	96.08 KB	96.08 KB	0% (0 B) 👌
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.pdb	26.21 MB	26.20 MB	--.02% (-8.00 KB) 💪
/libdatadog-x64-windows/release/static/datadog_profiling_ffi.lib	52.22 MB	52.20 MB	--.03% (-18.11 KB) 💪

libdatadog-x86-windows

Artifact	Baseline	Commit	Change
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.dll	23.82 MB	23.82 MB	--.01% (-4.00 KB) 💪
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.lib	97.58 KB	97.58 KB	0% (0 B) 👌
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.pdb	190.43 MB	190.42 MB	-0% (-8.00 KB) 👌
/libdatadog-x86-windows/debug/static/datadog_profiling_ffi.lib	788.61 MB	787.13 MB	--.18% (-1.48 MB) 💪
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.dll	6.96 MB	6.95 MB	--.05% (-4.00 KB) 💪
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.lib	97.58 KB	97.58 KB	0% (0 B) 👌
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.pdb	28.19 MB	28.17 MB	--.05% (-16.00 KB) 💪
/libdatadog-x86-windows/release/static/datadog_profiling_ffi.lib	49.70 MB	49.69 MB	--.03% (-17.38 KB) 💪

x86_64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.a	81.45 MB	81.43 MB	--.02% (-20.65 KB) 💪
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.so	9.41 MB	9.41 MB	0% (0 B) 👌

x86_64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.a	97.22 MB	97.20 MB	--.02% (-21.08 KB) 💪
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.so	11.46 MB	11.46 MB	-0% (-1.04 KB) 👌

github-actions Bot added the mini-agent label Sep 3, 2026

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perf(trace): encode agentless IDs without formatting - #2452

perf(trace): encode agentless IDs without formatting#2452
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BridgeAR/2026-09-03-agentless-hex-ids

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BridgeAR commented Sep 3, 2026

What does this PR do?

Motivation

Additional Notes

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github-actions Bot commented Sep 3, 2026

📚 Documentation Check Results

📦 libdd-trace-utils - 765 warning(s)

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🔒 Cargo Deny Results

📦 libdd-trace-utils - 3 error(s)

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Benchmarks

Comparison

Explanation

More details about the CI and significant changes

scenario:otlp/e2e_json/1x1000

scenario:otlp/encode_json/1x1000

scenario:vec_map/as_deduped_map/needs_dedup_1_in_4/8

Explanation

More details about the CI and significant changes

scenario:datadog_sample_span/multiple_rules_last_match/wall_time

scenario:glob_matcher/unicode_pattern_wildcard_match/wall_time

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Baseline

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📦 `libdd-trace-utils` - 765 warning(s)

📦 `libdd-trace-utils` - 3 error(s)

datadog-prod-us1-5 Bot commented Sep 3, 2026 •

edited by datadog-datadog-us1-prod Bot

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