ic-metrics

Allocation-free, dependency-free measurement arithmetic.

The no_std library exports record_sample for consumer-owned count/total fields, MeasurementAggregate for mergeable count/total/maximum, and MeasurementSummary for ordered observations with a latest value. MeasurementHistogram adds a mergeable fixed-size distribution with caller-selected bounds. Zero is a valid observation; an empty summary has no latest or maximum value. Tracked count and total clip independently, with sticky actual-overflow flags. Counts and individual samples use u64; totals and means use u128. Every exact counted batch fits its total. An exactly reached numeric cap remains exact. Consumers establish units, identity and reset boundaries before comparing observations; saturated totals cannot supply exact interval arithmetic.

use ic_metrics::MeasurementSummary;

let mut summary = MeasurementSummary::EMPTY;
assert_eq!(summary.latest(), None);
summary.record(0);
assert_eq!(summary.samples(), 1);
assert_eq!(summary.latest(), Some(0));

Tracked MeasurementAggregate::mean() and MeasurementSummary::mean() return Result<Option<u128>, MeasurementMeanError>: empty is None, measured zero is Some(0), and exact means round down. Actual overflow returns a typed error; exactly reaching the cap remains valid. The raw-field checked_mean(samples, total) stays conservative at either numeric cap because external fields do not carry overflow provenance. Accumulator flags cannot restore a clamped input sample.

MeasurementAggregate::merge combines count/total and maximum without claiming ordering or deduplication. interval_since(previous) returns checked count/total differences and mean after the owner establishes common identity, units and append-only continuity. It rejects actual overflow and numeric discontinuity; maximum and latest values cannot be subtracted. Ordered summaries do not merge.

The working source prepares the 0.7.0 hard cut: totals and integer means are u128, including raw-field helpers and intervals. Consumers must coordinate report fields, codecs and public re-exports; narrower output needs checked conversion. The published 0.6 dependency below retains its released contract. The arithmetic core adds no reader or endpoint. Consumers own reset identity and any once-per-window overflow log or alert.

The pending optional stable adapter stores aggregates, summaries and histograms in one host-owned stable B-tree map using ic-memory's collection types. Namespaced records retain units, reset epochs, wide totals and overflow flags. Adding ic-metrics-stable is the opt-in; existing arithmetic callers remain volatile. The adapter requires Rust 1.88 on host and Wasm. Hosts own allocation/bootstrap, synchronization, write cadence and resets; the arithmetic core remains dependency-free and no_std on Rust 1.85.

The application guide is included in packaged crate documentation, with a compiled example of fixed named histograms, separate units and event counts. It covers sample admission, async attribution, resets, reporting and cost qualification; applications own those policies.

For a distribution, construct MeasurementHistogram::new([10, 100]). Its disjoint buckets cover 0..=10 and 11..=100; overflow() counts larger observations. bucket_counts() returns those two counts, and aggregate() includes every observation. Duplicate or descending bounds return a typed HistogramBoundsError identifying the invalid bound. Construction and recording support constant evaluation. Storage is fixed, recording searches at most the configured number of bounds, and every bucket saturates independently. Buckets describe ranges; they do not provide exact percentiles. Units, thresholds and export encoding remain consumer-owned. merge(&other) requires matching bounds and returns a typed mismatch without changing the destination. Bucket and overflow saturation flags distinguish exact caps from lost counts.

cumulative_count(index) provides exact counts through a configured bound and quantile_bucket(numerator, denominator) for nearest-rank ranges, such as p95 with (95, 100). Empty quantiles are None; required count saturation returns HistogramQueryError. Overflow has no configured ceiling. checked_scaled_ratio(numerator, denominator, scale) floors an exact scaled integer ratio from a u128 numerator, without floating point or overflowing intermediate multiplication. Callers establish exact inputs and handle empty or saturated diagnostics before using it. Consumer adoption remains separately qualified.

Known callers are IcyDB, Canic, ic-timers, ic-backup, IC Blob Storage's restoration test probe and Toko Miner's production game-shard action metrics. Their attribution, registries, callback roles, replication, persistence and reporting remain local. ic-backup's host integration measures local durations in nanoseconds and prepared chunk sizes in bytes, with a four-bound byte histogram in the inspected implementation. Its diagnostics establish no IC instruction or cycle cost. The crate has no global consumer registry, stable-memory allocation or endpoints. Consumers own their summary and histogram instances, labels and persistence policy. The extraction contract records scope and evidence.

Platform reads belong in consumer adapters: IcyDB and Canic use ic_cdk::api::call_context_instruction_counter(); IC Timers uses its existing ic0::performance_counter(1) binding. Both read counter 1. Consumers own target gating, native handling, call-context identity and attribution. IcyDB's inclusive overlapping spans and Canic's exclusive endpoint accounting remain different consumer contracts.

Measuring cost

Measure raw canister Wasm bytes, IC instructions and actual cycle charges separately. The shared arithmetic allocates nothing; labels, map updates and report encoding are consumer costs. Build profiles belong to the consumer workspace. The performance audit records historical compiler checks and size/instruction/cycle comparisons for the retired reader test canister, with their workload limits. It does not establish consumer savings.

The separate consumer lookup measurements cover IcyDB and Canic's borrowed-key changes. Their isolated IC fixtures show lower instruction work and cycle charges for repeated keys, but higher costs for first insertions. Use the recorded workload and artifact identities when assessing those consumer changes; upgrading ic-metrics alone does not apply them.

The two-bound histogram cost experiment compares Canic's source-copied recording path with count/total, summary and histogram storage. It measures IC instructions and actual cycle charges in Linux PocketIC, plus raw Wasm bytes and target-specific slot sizes. Its repeated-key, two-bound workload does not establish whole-application cost or histogram adoption. Its original replay inputs are unavailable. The separate durable arithmetic replay provides a checksum-bound bundle of new fixture sources, locks, raw results and measured Wasms. It measures direct arithmetic without Canic lookup or attribution; its observations have their own source and workload identity.

The 0.6 arithmetic comparison measures recording, merging already prepared batches and reporting queries on exact released sources. The separate quantile fast-path comparison isolates the checked narrow-product improvement and its wide-product fallback cost. Both retain reproducible sources, locks, Wasms and raw IC readings. Batch preparation is excluded from merge costs; these synthetic workloads do not qualify consumer applications. Compute distribution queries during reporting when possible, rather than on every recorded observation.

Development

Use rustup with the pinned Rust 1.99.0 toolchain, Git, GNU Make and Bash 3.2 or newer. Install wasm32-unknown-unknown for Wasm checks. The arithmetic library's minimum compiler is Rust 1.85.0.

The private Wasm evidence inspector requires Rust 1.88.0. It uses IC Host libraries to report raw/encoded bytes and structural counts for explicitly supplied Wasms with caller-selected bounds, without executing a canister. Bare Cargo commands select the arithmetic package.

Prepare and check the reviewed tools, select their paths, then install the repository's formatting hook:

make install-tools
make tools-check
export PATH="$PWD/.tools/host/bin:$PWD/.tools/ic/bin:$PWD/.tools/rust/common/bin:$PATH"
make install-hooks

Local setup owns bootstrap prerequisites, tool inventory, shared storage, installer failure handling and PATH selection. Git hook rules own staged formatting and hook installation. The reviewed shared tooling is vendored; normal commands need no Shared Tooling sibling checkout.

make fmt sorts workspace manifests and formats Rust; make fmt-check checks without editing. make help lists focused commands. Select named tests during implementation, and use make check, make check-wasm, make clippy and make wasm-inspect-check for the affected package. Completed code delivery uses make ci, make msrv, make stable-msrv and make wasm-inspect-msrv; inspection and documentation changes use narrower checks. The host support and qualification guide owns local gates and native acceptance. Agent rules own command authority.

Common IC executable setup and PocketIC ownership are documented in IC tools. Metrics has no active server caller or Testkit dependency. Repository maintenance procedures live in the task catalog.

Releases and adoption

Declare the current arithmetic contract in the consumer's root catalog:

[workspace.dependencies]
ic-metrics = "0.6.5"

Members inherit with ic-metrics = { workspace = true }. Published consumers resolve the registry package; consumers exposing shared types coordinate the same released dependency identity. The changelog owns release history and required hard-cut changes. The extraction contract and consumer qualification issue own integration scope and acceptance; the current handoff distinguishes local preparation, publication and hosted qualification.

Contributions follow the shared contribution rules. Maintainer releases use make release-patch, make release-minor or make release-major under the shared release contract. This repository supports RELEASE_DELIVERY=direct only, defaulting to remote origin and branch main. Release execution requires cargo-edit (cargo set-version). The shared contract owns preparation, validation, commit/tag delivery and interrupted-release recovery.

Publication is separate from release delivery:

make publish-check
make publish

publish-check is Cargo's dry run; publish uploads only the existing ic-metrics and ic-metrics-stable package versions to crates.io in dependency order, using normal Cargo credentials and locked dependencies. Both retain Cargo's package verification and dirty-tree rejection. Publication does not bump versions, create Git commits/tags or clean artifacts. See Cargo's publication documentation.