perf(trace): write agentless JSON directly by BridgeAR · Pull Request #2454 · DataDog/libdatadog

BridgeAR · 2026-09-03T11:22:09Z

What does this PR do?

Writes fixed agentless JSON framing and field names directly into the output buffer. serde_json still owns every dynamic key, value, escape, and MessagePack conversion.

Motivation

The generic serializer state machine adds overhead for a fixed wire schema.

Additional Notes

This draft is stacked on the fixed-ID branch and contains only the JSON writer layer. Position-balanced Criterion runs improved that baseline by 35.44% for common HTTP traces and 20.18% for span-link traces.

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.

Write the fixed agentless payload structure directly while retaining serde_json for all dynamic keys and values. With production-deduplicated spans, position-balanced Criterion runs on macOS arm64 improved the fixed-ID baseline by 35.44% for common HTTP traces and 20.18% for span-link traces.

github-actions · 2026-09-03T11:24:00Z

📚 Documentation Check Results

⚠️ 765 documentation warning(s) found

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

Updated: 2026-09-03 11:23:59 UTC | Commit: bf6d802 | missing-docs job results

github-actions · 2026-09-03T11:25:56Z

🔒 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 11:25:55 UTC | Commit: bf6d802 | dependency-check job results

datadog-datadog-prod-us1 · 2026-09-03T11:32:44Z

✅ All CI checks and tests passed.

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

🎯 Code Coverage (details)
• Patch Coverage: 97.26%
• Overall Coverage: 77.12% (+0.07%)

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

🔗 Commit SHA: 3906b52 | Docs | View more details | Give us feedback!}

pr-commenter · 2026-09-03T11:55:32Z

Benchmarks

Comparison

Benchmark execution time: 2026-09-03 11:53:57

Comparing candidate commit 3906b52 in PR branch BridgeAR/2026-09-03-agentless-direct-json with baseline commit f194c4f in branch BridgeAR/2026-09-03-agentless-hex-ids.

Found 4 performance improvements and 2 performance regressions! Performance is the same for 139 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:agentless_encoding/common_http/20x5

🟩 execution_time [-10.802µs; -10.727µs] or [-8.408%; -8.350%]
🟩 throughput [+70936.061op/s; +71452.368op/s] or [+9.113%; +9.179%]

scenario:agentless_encoding/http_with_span_links/20x5

🟩 execution_time [-10.135µs; -10.046µs] or [-7.082%; -7.020%]
🟩 throughput [+52762.661op/s; +53246.217op/s] or [+7.551%; +7.620%]

scenario:vec_map/dedup/dup_1_in_4/16

🟥 execution_time [+99.717ns; +109.265ns] or [+11.130%; +12.195%]

scenario:vec_map/dedup/no_duplicates/16

🟥 execution_time [+39.780ns; +48.588ns] or [+5.881%; +7.184%]

Benchmark execution time: 2026-09-03 11:50:44

Comparing candidate commit 3906b52 in PR branch BridgeAR/2026-09-03-agentless-direct-json with baseline commit f194c4f in branch BridgeAR/2026-09-03-agentless-hex-ids.

Found 0 performance improvements and 1 performance regressions! Performance is the same for 74 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/resource_pattern_rule_matching/wall_time

🟥 execution_time [+13.724ns; +13.871ns] or [+5.357%; +5.414%]

Candidate

Omitted due to size.

Baseline

Omitted due to size.

dd-octo-sts · 2026-09-03T12:02:42Z

Artifact Size Benchmark Report

aarch64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.so	8.45 MB	8.45 MB	0% (0 B) 👌
/aarch64-alpine-linux-musl/lib/libdatadog_profiling.a	91.30 MB	91.33 MB	+.02% (+25.00 KB) 🔍

aarch64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.a	102.61 MB	102.64 MB	+.02% (+24.03 KB) 🔍
/aarch64-unknown-linux-gnu/lib/libdatadog_profiling.so	11.38 MB	11.38 MB	-0% (-736 B) 👌

libdatadog-x64-windows

Artifact	Baseline	Commit	Change
/libdatadog-x64-windows/debug/dynamic/datadog_profiling_ffi.dll	27.33 MB	27.31 MB	--.06% (-18.50 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	185.35 MB	--.02% (-56.00 KB) 💪
/libdatadog-x64-windows/debug/static/datadog_profiling_ffi.lib	805.24 MB	804.22 MB	--.12% (-1.01 MB) 💪
/libdatadog-x64-windows/release/dynamic/datadog_profiling_ffi.dll	9.01 MB	9.01 MB	+0% (+512 B) 👌
/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	26.22 MB	+.02% (+8.00 KB) 🔍
/libdatadog-x64-windows/release/static/datadog_profiling_ffi.lib	52.22 MB	52.22 MB	+.01% (+5.44 KB) 🔍

libdatadog-x86-windows

Artifact	Baseline	Commit	Change
/libdatadog-x86-windows/debug/dynamic/datadog_profiling_ffi.dll	23.82 MB	23.81 MB	--.06% (-17.00 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	190.34 MB	--.04% (-88.00 KB) 💪
/libdatadog-x86-windows/debug/static/datadog_profiling_ffi.lib	788.61 MB	786.44 MB	--.27% (-2.17 MB) 💪
/libdatadog-x86-windows/release/dynamic/datadog_profiling_ffi.dll	6.96 MB	6.96 MB	+.02% (+1.50 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	28.19 MB	0% (0 B) 👌
/libdatadog-x86-windows/release/static/datadog_profiling_ffi.lib	49.70 MB	49.71 MB	+.01% (+8.72 KB) 🔍

x86_64-alpine-linux-musl

Artifact	Baseline	Commit	Change
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.a	81.45 MB	81.46 MB	+0% (+7.46 KB) 👌
/x86_64-alpine-linux-musl/lib/libdatadog_profiling.so	9.41 MB	9.41 MB	+.04% (+4.00 KB) 🔍

x86_64-unknown-linux-gnu

Artifact	Baseline	Commit	Change
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.a	97.22 MB	97.23 MB	+0% (+7.64 KB) 👌
/x86_64-unknown-linux-gnu/lib/libdatadog_profiling.so	11.46 MB	11.46 MB	+.02% (+3.02 KB) 🔍

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

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perf(trace): write agentless JSON directly - #2454

perf(trace): write agentless JSON directly#2454
BridgeAR wants to merge 1 commit into
BridgeAR/2026-09-03-agentless-hex-idsfrom
BridgeAR/2026-09-03-agentless-direct-json

BridgeAR commented Sep 3, 2026

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BridgeAR commented Sep 3, 2026

What does this PR do?

Motivation

Additional Notes

How to test the change?

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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:agentless_encoding/common_http/20x5

scenario:agentless_encoding/http_with_span_links/20x5

scenario:vec_map/dedup/dup_1_in_4/16

scenario:vec_map/dedup/no_duplicates/16

Explanation

More details about the CI and significant changes

scenario:datadog_sample_span/resource_pattern_rule_matching/wall_time

Candidate

Baseline

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

📦 `libdd-trace-utils` - 3 error(s)

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

edited by datadog-prod-us1-6 Bot

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