Moon Log Schema

Structured tracing fields emitted by Moon's tracing instrumentation. All fields use tracing::instrument attributes with explicit field names — no unbounded cardinality.

Sampling

• Default: 1/1000 for normal spans, full capture on error
• Override: RUST_LOG=moon=debug for full tracing (development only)
• Future: --trace-sample-rate CLI flag (gated behind otel feature)

Span Fields

Connection Lifecycle

Span	Fields	Cardinality
handle_connection	peer_addr, client_id, shard_id	bounded (IP + u64 + usize)
handle_connection_sharded_monoio	peer_addr, client_id	bounded

Replication

Span	Fields	Cardinality
replication_handshake	replica_id, master_host	bounded (u64 + hostname)

Persistence

Span	Fields	Cardinality
aof_rewrite	seq (manifest sequence)	bounded (u64)
rotate_segment	(no custom fields — uses function-level span)	N/A

Vector Search

Span	Fields	Cardinality
compact_segment	(no custom fields)	N/A

Key Logging Rules

1. Keys are never logged verbatim. If a key appears in a log line, it must be hashed (e.g., xxh64(key)) to prevent unbounded cardinality and PII exposure.
2. Command names are logged via sanitize_cmd_label() which maps to a fixed set of ~120 known commands + "unknown" catch-all.
3. Error messages from client commands are logged at WARN level with the command name but not the key or arguments.
4. Shard IDs are small integers (0..num_shards), bounded by server config.

Log Levels

Level	Usage
ERROR	Unrecoverable I/O failures, persistence corruption, TLS errors
WARN	Recoverable errors (malformed input, slow subscriber drops, AOF write failures)
INFO	Server lifecycle (startup, shutdown, config changes, WAL rotation)
DEBUG	Per-connection lifecycle, SPSC drain, replication state changes
TRACE	Per-frame parsing, per-command dispatch (extremely verbose)