rustfs/docs/operations/scanner-benchmark-runbook.md

Scanner Benchmark Runbook

This runbook describes how to collect reproducible evidence for scanner pressure, scanner progress, and scanner runtime tuning. It is intended for maintainers and operators validating scanner changes in an isolated test deployment.

Use this runbook together with Scanner Runtime Controls. The runtime controls document explains each field and configuration key; this document explains how to run a comparable before/after observation and decide whether the scanner is healthier after tuning.

Scope

This runbook verifies that scanner pacing and cycle controls reduce background pressure while preserving maintenance progress. It is useful for:

• mostly idle single-node, single-disk deployments with many small objects;
• single-node multi-disk or erasure-set deployments where scanner work is spread across disks and sets;
• distributed clusters where scanner pressure is mixed with lifecycle, replication, heal, or bitrot queues;
• lifecycle expiry or transition backlog investigations;
• bucket replication repair backlog investigations;
• scanner-originated heal or bitrot admission investigations;
• pull request evidence when scanner behavior, scanner status, or scanner controls change.

This runbook does not prove full MinIO parity, site-replication correctness, or replaced-disk heal correctness. Those flows need dedicated distributed tests because their failure modes are not limited to scanner pacing.

Safety

Run the workload only in a disposable test environment. The commands below can create many buckets and objects and can overwrite runtime scanner settings.

Record the current scanner and heal configuration before changing anything:

mkdir -p artifacts
mc admin config get ALIAS scanner > artifacts/scanner-config.before.txt
mc admin config get ALIAS heal > artifacts/heal-config.before.txt

Replace ALIAS, endpoint, and credentials with values for the test deployment. Do not paste production credentials into saved artifacts.

Required Tools

• mc or a compatible admin client for config changes.
• awscurl or another SigV4-capable HTTP client for /v3/scanner/status.
• jq for status extraction.
• pidstat, mpstat, iostat, top, or equivalent host telemetry.
• warp, s3bench, or the repository object benchmark scripts for workload generation.

Test Matrix

At minimum, collect two runs on the same RustFS commit and the same workload:

Run	Purpose	Example scanner settings
Baseline	Observe current behavior without additional pacing changes.	Existing config.
Pacing override	Measure whether cooperative scanner sleeps reduce pressure.	scanner.delay="30" and scanner.max_wait="15".

Add bounded-cycle runs when a single scan cycle is too long:

Run	Purpose	Example scanner settings
Duration budget	Bound wall-clock time per cycle.	scanner.cycle_max_duration="1800".
Object budget	Bound objects processed per cycle.	scanner.cycle_max_objects="1000000".
Directory budget	Bound directories entered per cycle.	scanner.cycle_max_directories="100000".

When comparing runs, keep hardware, RustFS commit, object count, object size, bucket count, scanner-enabled state, and foreground workload constant.

Deployment Matrix

Use the smallest deployment that reproduces the symptom, but do not treat single-node validation as the whole scanner test surface. Scanner changes that touch queues, admission, or cross-node maintenance should include a distributed run when practical.

Deployment	What it validates	Minimum evidence
Single-node, single-disk	Small-object scanner pressure, pacing, cycle interval, and basic progress.	Scanner status time series plus host CPU and disk telemetry.
Single-node, multi-disk or erasure set	Set and disk scan concurrency, cycle budgets, checkpoint movement, usage cache persistence, and active path age.	Scanner status time series, per-disk host telemetry, and before/after data usage freshness.
Distributed cluster	Lifecycle transition queues, bucket replication repair admission, scanner-originated heal and bitrot admission, and queue/backlog pressure under cross-node work.	Scanner status time series from the cluster, host telemetry from each node, and subsystem-specific queued/skipped/missed counters.

The single-node, single-disk run is the baseline because it is cheap and repeatable. It is not sufficient for PRs that claim to improve distributed queue behavior, replication repair, or heal/bitrot admission.

Workload Shape

For the baseline small-object scanner-pressure run, use a workload that creates many small objects and then leaves the service mostly idle while the scanner walks the namespace. A useful minimum shape is:

• one RustFS node;
• one data disk;
• several buckets;
• at least 100,000 small objects total;
• scanner enabled;
• no sustained foreground workload during the observation window.

For a distributed backlog run, use the same structure but add the relevant subsystem condition, such as lifecycle rules, a bucket replication target, or a configured heal/bitrot scenario. Keep the status and host telemetry cadence the same so the result remains comparable with the baseline run.

The repository object benchmark script can generate object traffic if warp or s3bench is installed:

scripts/run_object_batch_bench.sh \
  --tool warp \
  --endpoint http://127.0.0.1:9000 \
  --access-key "$RUSTFS_ACCESS_KEY" \
  --secret-key "$RUSTFS_SECRET_KEY" \
  --bucket scanner-bench \
  --auto-new-bucket \
  --concurrency 64 \
  --duration 10m \
  --sizes 1KiB,4KiB,16KiB \
  --warp-mode put \
  --out-dir artifacts/object-load

If the object generator cannot create enough objects in one run, repeat the same command with new buckets or prefixes and record the final object count.

Status Collection

Capture scanner status before the workload, after the workload finishes, and throughout the idle observation window.

The repository includes a scanner validation harness for repeatable collection:

export RUSTFS_ACCESS_KEY="<admin-access-key>"
export RUSTFS_SECRET_KEY="<admin-secret-key>"

scripts/run_scanner_validation_harness.sh \
  --alias ALIAS \
  --endpoint http://127.0.0.1:9000 \
  --deployment single-disk \
  --workload-label small-object-idle \
  --samples 30 \
  --interval-secs 60 \
  --out-dir artifacts/scanner-validation

The harness writes scanner/heal config snapshots, scanner status samples, host telemetry when available, run metadata, and scanner-summary.csv.

Example status request:

awscurl \
  --service s3 \
  --region us-east-1 \
  --access_key "$RUSTFS_ACCESS_KEY" \
  --secret_key "$RUSTFS_SECRET_KEY" \
  --request GET \
  'http://127.0.0.1:9000/rustfs/admin/v3/scanner/status' \
  | jq . > "artifacts/scanner-status.$(date -u +%Y%m%dT%H%M%SZ).json"

For a time series, sample once per minute:

mkdir -p artifacts/status
while sleep 60; do
  ts="$(date -u +%Y%m%dT%H%M%SZ)"
  awscurl \
    --service s3 \
    --region us-east-1 \
    --access_key "$RUSTFS_ACCESS_KEY" \
    --secret_key "$RUSTFS_SECRET_KEY" \
    --request GET \
    'http://127.0.0.1:9000/rustfs/admin/v3/scanner/status' \
    | jq . > "artifacts/status/scanner-status.${ts}.json"
done

Stop the loop after the planned observation window.

Host Telemetry

Collect host metrics over the same window as scanner status.

pidstat -p "$(pidof rustfs)" 60 > artifacts/pidstat.txt
iostat -xz 60 > artifacts/iostat.txt
mpstat 60 > artifacts/mpstat.txt

If pidstat is not available, use top, ps, or the platform monitoring system, but keep the sampling interval and observation window in the report.

Runtime Tuning Examples

Persistent scanner config values use seconds for time fields. Use numeric strings instead of duration suffixes:

mc admin config set ALIAS scanner delay="30" max_wait="15"
mc admin config set ALIAS scanner cycle="3600"
mc admin config set ALIAS scanner cycle_max_duration="1800"
mc admin config set ALIAS scanner cycle_max_objects="1000000"
mc admin config set ALIAS scanner cycle_max_directories="100000"

The canonical persistent bitrot cadence belongs to the heal subsystem:

mc admin config set ALIAS heal bitrot_cycle="2592000"

Environment variables take precedence over persisted config and should be recorded separately:

RUSTFS_SCANNER_DELAY=30
RUSTFS_SCANNER_MAX_WAIT_SECS=15
RUSTFS_SCANNER_CYCLE=3600
RUSTFS_SCANNER_CYCLE_MAX_DURATION_SECS=1800
RUSTFS_SCANNER_CYCLE_MAX_OBJECTS=1000000
RUSTFS_SCANNER_CYCLE_MAX_DIRECTORIES=100000
RUSTFS_SCANNER_BITROT_CYCLE_SECS=2592000

After each config change, read scanner status and confirm the effective value and source under runtime_config.

Observation Window

Use the same window for each run:

1. Generate or verify the object namespace.
2. Wait until foreground workload is idle.
3. Save scanner and heal config.
4. Save one scanner status snapshot.
5. Collect scanner status and host telemetry for at least 30 minutes, or for one complete scanner cycle when that is practical.
6. Save one final scanner status snapshot.

Longer windows are better for cycle interval comparisons. Short windows are acceptable for quick pressure checks only if the conclusion avoids changing defaults.

Fields To Compare

Compare these fields between baseline and tuned runs:

Field	Why it matters
runtime_config.*.value and runtime_config.*.source	Confirms the tested settings actually took effect.
metrics.pacing_pressure.primary_pressure	Shows whether pressure is from queues, budgets, pause activity, active scans, or no scanner pressure.
metrics.pacing_pressure.last_cycle_total_pause_ratio	Shows how much of the last cycle was cooperative scanner pause time.
metrics.current_cycle_objects_scanned	Confirms object scan progress during the current cycle.
metrics.current_cycle_directories_scanned	Confirms directory walk progress during the current cycle.
metrics.last_cycle_result	Confirms whether the previous cycle completed, stopped partially, or failed.
metrics.last_cycle_partial_reason	Shows which budget stopped a partial cycle.
metrics.last_cycle_partial_source	Shows which scanner work source consumed the stopping budget.
metrics.source_work	Shows cumulative work found, queued, skipped, missed, executed, and failed by source.
metrics.current_cycle_source_work	Shows which source is consuming the current scan cycle.
metrics.last_cycle_source_work	Shows which source consumed the previous scan cycle.
metrics.lifecycle_transition.scanner_missed	Shows scanner-discovered transition work that could not be queued.
metrics.lifecycle_transition.queue_full	Shows transition queue pressure outside the scanner walk itself.
metrics.scan_checkpoint	Confirms partial cycles preserve resume context.
metrics.oldest_active_path_age_seconds	Helps identify scanner paths that may be stuck.

Do not use a single CPU spike as the conclusion. Compare average and p95 CPU over the same observation window.

Interpreting Results

A useful tuning result has all of these properties:

• average or p95 scanner-related CPU and disk pressure decreases;
• current_cycle_objects_scanned or current_cycle_directories_scanned continues to advance;
• source_work.missed does not grow unexpectedly for lifecycle, replication, heal, or bitrot;
• last_cycle_result is either success or a partial result with a clear budget reason and checkpoint;
• data usage freshness remains acceptable for the tested deployment.

Treat these as failure signals:

• CPU drops only because the scanner stops making progress;
• primary_pressure stays at queued_scans while queues grow;
• last_cycle_partial_reason repeats forever with no checkpoint movement;
• lifecycle transition scanner_missed or queue_full grows during a run that was expected to reduce backlog;
• heal or bitrot work moves from queued to missed after a scanner pacing change.

PR Evidence Checklist

For scanner behavior PRs, include this evidence when available:

• RustFS commit SHA and branch.
• Deployment shape: node count, disk count, disk type, CPU count, memory, and object count.
• Workload command or script and benchmark artifact path.
• Scanner and heal config before and after tuning.
• Observation window and sample interval.
• Scanner status snapshots or time series.
• Host CPU and disk telemetry.
• Short conclusion that separates pressure reduction from scanner progress.

For documentation-only PRs, it is enough to verify links and formatting.