fix(metrics): encode units in V3 series payloads

[rayz]

Summary

This pr adds metric units encoding into V3 series payloads to match the Datadog Agent V3 serializer.

This change keeps sketch behavior unchanged: V3 sketches do not encode units, matching the Agent
sketch path.

Change Type

• Bug fix
• New feature
• Non-functional (chore, refactoring, docs)
• Performance

How did you test this PR?

unit tests / ci

References

[Copilot]

Pull request overview

Adds metric unit encoding to V3 series payloads, matching the Datadog Agent V3 serializer. Units are interned into a new dictionary and stored sparsely via a per-metric FLAG_HAS_UNIT bit and a parallel unit_refs column. Sketches deliberately do not encode units, mirroring Agent behavior.

Changes:

• Introduces FLAG_HAS_UNIT, a unit interner, dictionary bytes, and sparse unit_refs column in V3Writer, plus a V3MetricBuilder::set_unit API.
• Adds DICT_UNIT_STR_FIELD_NUMBER (25) and UNIT_REFS_FIELD_NUMBER (26) constants and serializes the new fields in finalize.
• Wires metric.metadata().unit() into the V3 writer for non-sketch metrics and adds unit tests + payload-level integration tests.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
lib/saluki-components/src/encoders/datadog/metrics/v3/constants.rs	Adds new V3 protobuf field numbers for unit dictionary and unit refs.
lib/saluki-components/src/encoders/datadog/metrics/v3/writer.rs	Implements sparse unit interning, encoding, delta-encoding, and serialization with new set_unit builder API and tests.
lib/saluki-components/src/encoders/datadog/metrics/mod.rs	Sets units on V3 builder for non-sketch metrics; adds payload-level tests verifying sparse unit refs and sketch exclusion.

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[pr-commenter]

Binary Size Analysis (Agent Data Plane)

Baseline: 1ad7cde · Comparison: 935bba5 · diff
Analysis Configuration: stripped binaries · Pass/Fail Threshold: +5%
Sizes: 37.65 MiB (baseline) vs 37.97 MiB (comparison)
Size Change: +328.72 KiB (+0.85%)

✅ Binary size difference within threshold

Changes by Module

Module	File Size	Symbols
saluki_components::encoders::datadog	+70.15 KiB	352
core	+53.94 KiB	14504
anyhow	+40.05 KiB	1699
alloc	+34.54 KiB	2403
hyper	+28.29 KiB	580
figment	+24.37 KiB	700
saluki_components::sources::otlp	-21.89 KiB	236
hashbrown	+16.21 KiB	1100
prost	-14.46 KiB	515
saluki_components::common::datadog	+13.66 KiB	440
chrono	-13.08 KiB	23
hyper_util	-12.11 KiB	137
http	+11.84 KiB	419
[sections]	+11.25 KiB	9
tower	+10.78 KiB	318
tracing	-10.19 KiB	175
axum	+9.75 KiB	422
serde_core	+9.49 KiB	888
tokio_rustls	+9.28 KiB	93
rustls	-8.78 KiB	41

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +1.6%  +327Ki  +1.6%  +258Ki    [46991 Others]
  [NEW]  +136Ki  [NEW]  +136Ki    agent_data_plane::cli::run::handle_run_command::_{{closure}}::hf265beba717a8ffb
  [NEW] +66.7Ki  [NEW] +66.5Ki    saluki_core::topology::built::BuiltTopology::spawn::_{{closure}}::hef6f38503239c166
  [NEW] +66.1Ki  [NEW] +66.0Ki    agent_data_plane::cli::run::create_topology::_{{closure}}::hdcdf70adbde87ffc
  [NEW] +58.7Ki  [NEW] +58.5Ki    agent_data_plane::internal::env::workload::build_collector::_{{closure}}::ha56b75595a60c965
  [NEW] +58.2Ki  [NEW] +58.0Ki    saluki_core::topology::blueprint::TopologyBlueprint::build::_{{closure}}::hacbbeaf29f1d76dc
  [NEW] +57.1Ki  [NEW] +56.9Ki    agent_data_plane::internal::env::ADPEnvironmentProvider::from_configuration::_{{closure}}::hb77df6cc347f39b1
  [NEW] +56.7Ki  [NEW] +56.5Ki    agent_data_plane::cli::debug::handle_debug_command::_{{closure}}::ha2e6796c57380dae
  [NEW] +56.0Ki  [NEW] +55.8Ki    agent_data_plane::cli::dogstatsd::handle_dogstatsd_command::_{{closure}}::hb45f834f247c7f00
  [NEW] +49.8Ki  [NEW] +49.5Ki    agent_data_plane::main::_{{closure}}::hafe55c655b44bc0f
  [NEW] +49.7Ki  [NEW] +49.6Ki    core::ops::function::FnOnce::call_once::he29f19ec791745c2
  [DEL] -48.9Ki  [DEL] -48.8Ki    core::ops::function::FnOnce::call_once::h669ff363e842dff3
  [DEL] -49.7Ki  [DEL] -49.4Ki    agent_data_plane::main::_{{closure}}::h7d49a9469c34b899
  [DEL] -56.5Ki  [DEL] -56.3Ki    agent_data_plane::cli::dogstatsd::handle_dogstatsd_command::_{{closure}}::he79b0808df75cda1
  [DEL] -56.6Ki  [DEL] -56.4Ki    agent_data_plane::cli::debug::handle_debug_command::_{{closure}}::h7c655b6902e2f89a
  [DEL] -57.1Ki  [DEL] -56.9Ki    agent_data_plane::internal::env::ADPEnvironmentProvider::from_configuration::_{{closure}}::ha0920a2b79b02cce
  [DEL] -57.8Ki  [DEL] -57.6Ki    saluki_core::topology::blueprint::TopologyBlueprint::build::_{{closure}}::h32219546faa6f65a
  [DEL] -58.4Ki  [DEL] -58.2Ki    agent_data_plane::internal::env::workload::build_collector::_{{closure}}::ha8e6b4b93de14a84
  [DEL] -66.2Ki  [DEL] -66.0Ki    saluki_core::topology::built::BuiltTopology::spawn::_{{closure}}::hfe1e9d26bba4c0cd
  [DEL] -66.3Ki  [DEL] -66.1Ki    agent_data_plane::cli::run::create_topology::_{{closure}}::h9611a56813a60eb8
  [DEL]  -136Ki  [DEL]  -136Ki    agent_data_plane::cli::run::handle_run_command::_{{closure}}::h4399bd59161f275e
  +0.9%  +328Ki  +0.8%  +259Ki    TOTAL

[rayz]

/merge

[gh-worker-devflow-routing-ef8351]

View all feedbacks in Devflow UI.

2026-05-28 19:40:47 UTC ℹ️ Start processing command /merge

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2026-05-28 19:40:48 UTC ℹ️ MergeQueue: Stack detected — automatically merging the entire stack.

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2026-05-28 19:40:58 UTC ℹ️ Devflow: Merging stacked PRs in the following order:

1. enhancement(metrics): support for metrics v3 protocol (#1175)
2. fix(metrics): encode units in V3 series payloads (#1761)

Progress updates will be sent here directly.

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2026-05-28 19:40:59 UTC ℹ️ Devflow: Merging enhancement(metrics): support for metrics v3 protocol (#1175)...

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2026-05-28 19:41:01 UTC ❌ MergeQueue

merge method 'merge' is not allowed for this repository. Supported methods are: [squash, rebase]

[pr-commenter]

Regression Detector (Agent Data Plane)

Run ID: 0dcd4722-02aa-4be6-98e7-a8970e01394a
Baseline: 1ad7cde2 · Comparison: 935bba59 · diff

Optimization Goals: ✅ No significant changes detected

Fine details of change detection per experiment (35)

Experiments configured erratic: true are tagged (ignored) and skipped when determining which experiments regressed or improved. Experiments which are detected as erratic at runtime are tagged (erratic) to flag that the run's sample dispersion was high, but their regression / improvement signal still counts.

experiment	goal	Δ mean %	links
dsd_uds_10mb_3k_contexts_cpu (erratic)	cpu	⚪ +6.29	metrics profiles logs
otlp_ingest_metrics_5mb_memory	memory	⚪ +1.66	metrics profiles logs
quality_gates_rss_idle	memory	⚪ +1.14	metrics profiles logs
otlp_ingest_traces_5mb_memory	memory	⚪ +0.79	metrics profiles logs
dsd_uds_512kb_3k_contexts_memory	memory	⚪ +0.69	metrics profiles logs
quality_gates_rss_dsd_low	memory	⚪ +0.65	metrics profiles logs
dsd_uds_100mb_3k_contexts_memory	memory	⚪ +0.57	metrics profiles logs
dsd_uds_10mb_3k_contexts_memory	memory	⚪ +0.50	metrics profiles logs
quality_gates_rss_dsd_medium	memory	⚪ +0.47	metrics profiles logs
dsd_uds_500mb_3k_contexts_memory	memory	⚪ +0.39	metrics profiles logs
dsd_uds_1mb_3k_contexts_memory	memory	⚪ +0.32	metrics profiles logs
otlp_ingest_traces_ottl_filtering_5mb_memory	memory	⚪ +0.30	metrics profiles logs
otlp_ingest_traces_ottl_transform_5mb_throughput	throughput	⚪ -0.25	metrics profiles logs
quality_gates_rss_dsd_heavy	memory	⚪ +0.21	metrics profiles logs
dsd_uds_500mb_3k_contexts_throughput	throughput	⚪ -0.10	metrics profiles logs
dsd_uds_100mb_3k_contexts_cpu (erratic)	cpu	⚪ +0.09	metrics profiles logs
otlp_ingest_metrics_5mb_throughput	throughput	⚪ -0.02	metrics profiles logs
otlp_ingest_traces_ottl_transform_5mb_cpu (erratic)	cpu	⚪ +0.01	metrics profiles logs
dsd_uds_10mb_3k_contexts_throughput	throughput	⚪ -0.00	metrics profiles logs
dsd_uds_512kb_3k_contexts_throughput	throughput	⚪ -0.00	metrics profiles logs
dsd_uds_1mb_3k_contexts_throughput	throughput	⚪ -0.00	metrics profiles logs
otlp_ingest_logs_5mb_throughput (ignored)	throughput	⚪ -0.00	metrics profiles logs
dsd_uds_100mb_3k_contexts_throughput	throughput	⚪ +0.00	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory	⚪ -0.29	metrics profiles logs
otlp_ingest_traces_ottl_transform_5mb_memory	memory	⚪ -0.30	metrics profiles logs
otlp_ingest_traces_ottl_filtering_5mb_throughput	throughput	⚪ +0.44	metrics profiles logs
otlp_ingest_traces_5mb_cpu (erratic)	cpu	⚪ -0.57	metrics profiles logs
otlp_ingest_logs_5mb_cpu (ignored)	cpu	⚪ -0.85	metrics profiles logs
dsd_uds_500mb_3k_contexts_cpu (erratic)	cpu	⚪ -0.91	metrics profiles logs
otlp_ingest_traces_5mb_throughput	throughput	⚪ +0.93	metrics profiles logs
otlp_ingest_logs_5mb_memory (ignored)	memory	⚪ -1.25	metrics profiles logs
otlp_ingest_traces_ottl_filtering_5mb_cpu (erratic)	cpu	⚪ -1.95	metrics profiles logs
otlp_ingest_metrics_5mb_cpu (erratic)	cpu	⚪ -2.33	metrics profiles logs
dsd_uds_512kb_3k_contexts_cpu (erratic)	cpu	⚪ -3.45	metrics profiles logs
dsd_uds_1mb_3k_contexts_cpu (erratic)	cpu	🟢 -11.83	metrics profiles logs

Bounds Checks: ✅ Passed (5)

experiment	check	replicates	observed	links
quality_gates_rss_dsd_heavy	memory_usage	10/10	✅ 123 MiB ≤ 140 MiB	metrics profiles logs
quality_gates_rss_dsd_low	memory_usage	10/10	✅ 40.1 MiB ≤ 50 MiB	metrics profiles logs
quality_gates_rss_dsd_medium	memory_usage	10/10	✅ 61.7 MiB ≤ 75 MiB	metrics profiles logs
quality_gates_rss_dsd_ultraheavy	memory_usage	10/10	✅ 178 MiB ≤ 200 MiB	metrics profiles logs
quality_gates_rss_idle	memory_usage	10/10	✅ 27.3 MiB ≤ 40 MiB	metrics profiles logs

Explanation

A change is flagged as a regression when |Δ mean %| > 5.00% in the regressing direction for its optimization goal AND SMP marks the experiment as a regression (is_regression: true). Improvements use the matching criteria for the improving direction. Experiments configured erratic: true (tagged (ignored)) are skipped outright; experiments detected as erratic at runtime (tagged (erratic)) still count, since that flag describes sample dispersion rather than directional certainty. The Δ mean % cell is colored accordingly: 🟢 = improvement, 🔴 = regression, ⚪ = neutral. Reduction in CPU or memory is an improvement; reduction in ingress throughput is a regression.