Core Purpose

The SHOW REPLICA STATUS instruction serves as a diagnostic utility for evaluating Write-Ahead Log (WAL) transmission health. It surfaces granular synchronization metrics, tracking byte-level offsets between the originating host and consuming standby instances.

Operational Constraints

• Invocation is restricted exclusively to the authoritative (primary) database node.
• Data projection aligns precisely with the underlying pg_stat_get_wal_senders() system catalog.

Syntax Blueprint

SHOW {SLAVE | REPLICA} STATUS [FOR CHANNEL channel_identifier]

Parameter Breakdown

• {SLAVE | REPLICA}: Semantic aliases functioning identically within the parser.
• [FOR CHANNEL channel_identifier]: Optional predicate enabling partial string matching against transport descriptors. Typically leveraged for isolating routes defined by subnet masks, port configurations, or custom tunnel labels.

Response Attributes

• pid: Operating system thread identifier managing the WAL dispatch process.
• sender_pid: Internal lightweight process handle mapped to the dispatcher.
• local_role: Architectural designation of the executing host.
• peer_role: Designation of the linked secondary node.
• peer_state: Runtime posture of the target replica.
• state: Lifecycle phase of the sender daemon.
• catchup_start / catchup_end: Temporal boundaries defining the initial data resynchronization window.
• sender_sent_location: Highest Log Sequence Number (LSN) queued for network delivery.
• sender_write_location: Maximum LSN committed to volatile memory buffers on the source.
• sender_flush_location: LSN checkpoint verified as durable on primary storage subsystems.
• sender_replay_location: LSN processed by the primary transaction engine.
• receiver_received_location: LSN acknowledged up on arrival at the destination stack.
• receiver_write_location: Buffer stage LSN recorded locally on the standby.
• receiver_flush_location: Persistent storage confirmation point on the replica side.
• receiver_replay_location: Transaction application frontier on the standby instance.
• sync_percent: Calculated delta representing replication fidelity.
• sync_state: Consistency classification (e.g., Sync, Async, Local).
• sync_priority: Numerical weight assigned to automatic failover election protocols.
• sync_most_available: Cluster policy indicator governing continuous operation guarantees.
• channel: Endpoint topology mapping source-to-destination connectivity details.

Execution Scenarios

Initiate a global sweep to assess all active replication tunnels:

openGauss=# SHOW REPLICA STATUS;

To restrict diagnostics to a specific network segment, apply substring filtering within the channel clause:

openGauss=# SHOW SLAVE STATUS FOR CHANNEL '16.0.8';

Evaluating replication lag requires calculating the hexadecimal difference between sender_sent_location and receiver_replay_location. A continuously expanding delta signals network congestion or receiver-side bottleneck, necessitating capacity review or workload redistribution.