Module metrics 

Metrics instrumentation for sync-engine.

Uses the metrics crate for backend-agnostic metrics collection. The parent daemon is responsible for choosing the exporter (Prometheus, OTEL, etc.)

Metric Naming Convention

• sync_engine_ prefix for all metrics
• _total suffix for counters
• _seconds suffix for duration histograms
• _bytes suffix for size histograms

Labels

• tier: L1, L2, L3
• operation: get, put, delete, batch
• status: success, error, rejected

Structs

LatencyTimer

A timing guard that records latency on drop

Functions

record_batch_bytes

Record batch bytes

record_batch_size

Record batch size

record_bytes_read

Record bytes read from a tier

record_bytes_written

Record bytes written to a tier

record_circuit_breaker_call

Record circuit breaker call outcome

record_circuit_call

Record circuit breaker call

record_connection_error

Record a connection/backend error

record_corruption

Record data corruption detection

record_cuckoo_check

Record cuckoo filter check

record_cuckoo_false_positive

Record cuckoo filter false positive

record_error

Record an error with category for alerting

record_eviction

Record eviction event

record_flush_duration

Record batch flush duration

record_items_written

Record items written

record_latency

Record operation latency

record_merkle_operation

Record merkle tree operation

record_operation

Record a successful sync operation

record_startup_phase

Record startup phase duration

record_startup_total

Record total startup time

record_timeout

Record a timeout error

record_wal_drain

Record WAL drain operation

set_backend_healthy

Set backend health status (1 = healthy, 0 = unhealthy)

set_backpressure_level

Set backpressure level (0 = None, 1 = Low, 2 = Medium, 3 = High, 4 = Critical)

set_batch_queue_bytes

Set batch queue size in bytes

set_batch_queue_items

Set batch queue depth (items pending flush)

set_circuit_state

Record circuit breaker state change

set_cuckoo_filter_entries

Set cuckoo filter entry count

set_cuckoo_filter_load

Set cuckoo filter capacity utilization (0.0 - 1.0)

set_engine_state

Set engine state (for monitoring state machine transitions)

set_l1_cache_bytes

Set current L1 cache size in bytes

set_l1_cache_items

Set current L1 cache item count

set_memory_pressure

Set memory pressure level (0.0 - 1.0)

set_wal_bytes

Set WAL file size in bytes

set_wal_entries

Set WAL pending entries