rustfs/crates/object-capacity/AGENTS.md

rustfs-object-capacity Agent Guide

This document is a lightweight maintainer-oriented guide for collaborators working in crates/object-capacity.

Purpose

rustfs-object-capacity is responsible for estimating and refreshing RustFS object-data usage, not general filesystem capacity. Changes in this crate can affect:

• admin used_capacity responses
• refresh latency and background work
• dirty-disk propagation after writes, heal, and data movement
• capacity-related metrics and operational observability

Keep changes narrow and source-driven.

Source of Truth

Before changing behavior, read these files first:

• src/scan.rs
• src/capacity_manager.rs
• src/capacity_scope.rs
• src/types.rs
• ../../rustfs/src/capacity/service.rs
• ../config/src/constants/capacity.rs

Do not treat shell scripts or old docs as the authoritative behavior definition when the Rust code says otherwise.

Change Priorities

Prefer the following order:

1. correctness of returned capacity values
2. safety of degraded behavior under timeout, stall, or partial failure
3. consistency of dirty-subset refresh and per-disk cache state
4. bounded scan cost and runtime overhead
5. clarity of metrics and logs

Important Behavioral Constraints

• This crate intentionally prefers a usable degraded result over hard failure when partial progress is available.
• Dirty-subset refresh is safe only after a complete per-disk cache has been established.
• Subset refresh failures with partial errors must not silently corrupt aggregate cache state.
• Environment-derived configuration is cached behind OnceLock in non-test builds, so runtime env changes usually require a restart.
• Symlink following is disabled by default for safety and determinism.
• Multi-disk scans are concurrent, so avoid changes that introduce hidden shared-state coupling.

Editing Guidance

• Keep scan-path changes local and easy to audit.
• Avoid refactoring the control flow unless it is necessary for correctness.
• Preserve the current exact-vs-estimated semantics unless the task explicitly changes them.
• Reuse existing configuration constants from rustfs-config instead of introducing duplicate literals.
• Treat metric names and labels as compatibility-sensitive unless the task explicitly allows a metric contract change.

Validation Guidance

For code changes, prefer focused verification close to the changed behavior:

• scan correctness tests in src/scan.rs
• manager/refresh-state tests in src/capacity_manager.rs
• scope propagation tests in src/capacity_scope.rs
• integration behavior in ../../rustfs/src/capacity/service.rs or related app tests when needed

Useful commands:

cargo test -p rustfs-object-capacity
cargo test -p rustfs-object-capacity --doc
cargo bench -p rustfs-object-capacity --bench capacity_scan

If the change is documentation-only, lightweight verification is enough.

Documentation Expectations

• Keep README.md in English.
• Keep README_ZH.md aligned when behavior or public usage changes.
• Prefer describing real behavior from code instead of aspirational architecture.

Common Pitfalls

• Assuming used_capacity means total disk usage instead of object-data usage.
• Forgetting that the initial full refresh is required before safe dirty-subset refresh.
• Forgetting that partial errors can still produce a returned result.
• Overlooking the fallback path that stores externally supplied disk-used capacity as DataSource::Fallback.
• Changing timeout or sampling behavior without reviewing the observable effects on degraded results and metrics.