Metrics Reference

PrkDB exports Prometheus metrics from the shared registry in crates/prkdb/src/prometheus_metrics.rs.

Where Metrics Are Exposed

• prkdb-server: http://<host>:9090 + NODE_ID/metrics
• prkdb-cli serve --prometheus: http://<host>:<port>/metrics

The HTTP server now re-exports the real Prometheus registry instead of placeholder counters.

Core Health Metrics

Metric	Type	Description
prkdb_up	Gauge	Server liveness by node_id
prkdb_collections_active	Gauge	Number of active collections
prkdb_collection_size_bytes	Gauge	Collection size by node_id and collection

Raft Metrics

Metric	Type	Description
prkdb_raft_state	Gauge	Current Raft state by node_id and partition
prkdb_raft_term	Gauge	Current term
prkdb_raft_commit_index	Gauge	Commit index
prkdb_raft_leader_elections_total	Counter	Total leader elections
prkdb_raft_heartbeats_sent_total	Counter	Heartbeats sent to peers
prkdb_raft_heartbeats_failed_total	Counter	Failed heartbeats
prkdb_raft_append_entries_total	Counter	AppendEntries RPCs by result
prkdb_raft_snapshot_index	Gauge	Last snapshot index

Snapshot Metrics

Metric	Type	Description
prkdb_snapshots_created_total	Counter	Snapshots created
prkdb_snapshot_creation_duration_seconds	Histogram	Snapshot creation latency

Operation Metrics

Metric	Type	Description
prkdb_ops_total	Counter	Total operations
prkdb_reads_total	Counter	Total reads
prkdb_writes_total	Counter	Total writes
prkdb_deletes_total	Counter	Total deletes
prkdb_delete_batches_total	Counter	Delete batch operations
prkdb_operation_duration_seconds	Histogram	Operation latency
prkdb_read_duration_seconds	Histogram	Read latency
prkdb_write_duration_seconds	Histogram	Write latency
prkdb_batch_duration_seconds	Histogram	Batch write latency

Cache Metrics

Metric	Type	Description
prkdb_cache_hits_total	Counter	Cache hits
prkdb_cache_misses_total	Counter	Cache misses
prkdb_cache_hit_ratio	Gauge	Cache hit ratio

Example Checks

curl http://127.0.0.1:9091/metrics | grep prkdb_up
curl http://127.0.0.1:9091/metrics | grep prkdb_raft_state
curl http://127.0.0.1:9091/metrics | grep prkdb_operation_duration_seconds

Alert Ideas

Node down

prkdb_up == 0

Frequent leader elections

rate(prkdb_raft_leader_elections_total[5m]) > 0

Heartbeat failures

rate(prkdb_raft_heartbeats_failed_total[5m]) > 0

High write latency

histogram_quantile(0.99, sum by (le) (rate(prkdb_write_duration_seconds_bucket[5m])))