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rustfs/docs/architecture/workload-admission-contracts.md
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Zhengchao An 05833063c7 refactor(concurrency): remove zero-caller facade modules, fix feature build (#4530)
refactor(concurrency): remove zero-caller facade modules and fix no-default-features build (backlog#1025)

The audit in rustfs/backlog#1010 (consistent with #805) established that most of crates/concurrency was a decorative facade with zero production callers; the real runtime concurrency control lives in rustfs/src/storage/*. This deletes the dead facades and keeps only what the workspace actually consumes.

Deleted (zero callers verified by workspace-wide grep):
- manager.rs: ConcurrencyManager, lifecycle start/stop, misleading 'started' lifecycle logs
- config.rs: ConcurrencyConfig, ConcurrencyFeatures, from_env
- timeout.rs: TimeoutManager, TimeoutGuard, TimeoutManagerPolicy
- lock.rs: LockManager, LockScopeGuard, OptimizedLockGuard
- scheduler.rs: SchedulerManager, SchedulerPolicy, IoStrategy
- deadlock.rs facade: DeadlockManager, RequestTracker
- backpressure.rs facade: BackpressureManager, BackpressurePipe
- the prelude module, unused io-core re-exports, and all feature flags

Kept (real callers in ecstore/heal/rustfs):
- workload.rs admission contract types (unchanged)
- workers.rs Workers pool (unchanged, retained per #4498)
- GetObjectQueueSnapshot (moved from manager.rs to new queue.rs)
- PipeBackpressurePolicy (used by rustfs/src/storage/backpressure.rs)
- DeadlockMonitorPolicy (used by rustfs/src/storage/deadlock_detector.rs)
- OperationProgress re-export (used by rustfs/src/storage/timeout_wrapper.rs)

Removing the feature flags fixes the previously broken cargo check -p rustfs-concurrency --no-default-features (E0432). Docs and the logging guardrail file list are updated to match.

Ref: rustfs/backlog#1025
2026-07-09 01:12:43 +08:00

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Markdown

# Workload Admission Contracts
This document records the `rustfs/backlog#660` PR-05 and PR-07 scheduler
preservation and runtime workload-class contract slice.
## Preservation Coverage
The `rustfs-concurrency` tests pin the current reusable admission-facing
behavior before later snapshot extraction:
- Worker slot over-release remains clamped by the configured worker limit.
- `GetObjectQueueSnapshot` preserves saturated, over-available, and zero-total
permit semantics.
The former reusable scheduler and backpressure-pipe facades (and their
preservation tests) were removed as zero-caller dead code in backlog#1025;
scheduler buffer/priority behavior is now pinned by `rustfs-io-core` and
`rustfs/src/storage/concurrency` tests.
## Workload Class Contract
`WorkloadClass` defines the required future admission categories:
- Foreground read.
- Foreground write.
- Metadata.
- Scanner.
- Repair.
- Replication.
`AdmissionState`, `WorkloadAdmissionSnapshot`, and
`WorkloadAdmissionRegistrySnapshot` define read-only status shapes for later
runtime owners. They do not replace the current scheduler, request guard,
scanner, heal, replication, or ECStore placement behavior.
## Boundary Rules
- `rustfs-concurrency` owns this reusable contract surface.
- The contract does not depend on `rustfs-ecstore` or RustFS binary runtime
state.
- No scheduler decision logic, queue capacity, Tokio runtime default, scanner
admission, heal admission, replication admission, placement, membership, or
NUMA behavior changes are part of this slice.
## Set-Local Snapshot Extraction
The RustFS storage `ConcurrencyManager` now implements
`WorkloadAdmissionSnapshotProvider` for local foreground-read admission:
- `ForegroundRead` reports local disk-read permit usage through
`GetObjectQueueSnapshot`.
- `active` is the number of disk-read permits currently in use.
- `limit` is the configured maximum concurrent disk reads.
- `queued` remains `None` because the current semaphore does not expose waiter
counts.
- Scanner, repair, replication, foreground write, and metadata entries remain
`Unknown` until their owning runtime components expose read-only status.
This is an observation surface only. Permit acquisition, priority assignment,
buffer sizing, storage media detection, request guards, and queue behavior are
unchanged.
## Heal Repair Snapshot Extraction
The RustFS integration layer now exposes a read-only repair admission snapshot
from the heal runtime counters:
- `Repair` reports the current heal active task count.
- `queued` reports the current heal queue length.
- `limit` remains `None` because the configured heal queue and concurrency
limits live behind the async heal manager state.
- Other workload classes remain `Unknown` in this provider until their owning
runtime components expose read-only status.
This is an observation surface only. Heal request admission, queue capacity,
priority merge/drop policy, task scheduling, retry handling, and repair
behavior are unchanged.
## Replication Snapshot Extraction
The RustFS integration layer now exposes a read-only replication admission
snapshot from the existing replication pool and queue statistics:
- `Replication` reports active regular, large-object, and MRF worker counts.
- `queued` reports the current site replication queue count when queue stats
are immediately observable.
- `limit` remains `None` because replication worker limits remain owned by the
async replication pool and resize policy.
- If the replication runtime has not initialized, or queue stats are currently
locked, the snapshot reports `Unknown` instead of blocking or guessing.
This is an observation surface only. Replication admission, queue channel
capacity, worker resize behavior, MRF handling, target dispatch, and resync
behavior are unchanged.
## RustFS Runtime Owner Snapshot Extraction
The RustFS integration layer now extends the workload admission registry with
additional read-only owner mappings:
- `ForegroundRead` reuses the storage `ConcurrencyManager` disk-read permit
snapshot so the RustFS-level provider exposes the same active and limit
counts as the storage-local provider.
- `Scanner` reports the existing scanner active work-unit counter. When the
counter is zero, the snapshot remains `Unknown` because the current counter
cannot distinguish an idle scanner from a scanner that has not initialized.
- `Metadata` reports `Open` once the bucket metadata runtime handle is
available, and `Unknown` before initialization.
- `ForegroundWrite` remains `Unknown` until a write-specific admission owner
exposes a read-only surface.
This is an observation surface only. Disk-read permit acquisition, scanner
cycle scheduling, bucket metadata loading, metadata locks, object write paths,
and queue behavior are unchanged.
## Provider Composition Boundary
`WorkloadAdmissionRegistrySnapshot::overlay` composes provider-owned registry
snapshots without mutating runtime owners:
- The storage concurrency provider remains the source of truth for
`ForegroundRead`.
- The RustFS runtime owner provider overlays metadata, scanner, repair,
replication, and foreground-write status on top of the storage registry.
- Matching workload classes are replaced by the later provider snapshot; new
classes are appended without reordering existing unrelated entries.
This keeps the later controller/status layer consuming a single read-only
registry while preserving the existing storage, scanner, heal, replication, and
metadata ownership boundaries.