MCP Toolbox for Databases

--- title: "postgres-replication-stats" type: docs weight: 1 description: > The "postgres-replication-stats" tool reports replication-related metrics for WAL streaming replicas, including lag sizes presented in human-readable form. aliases: - /resources/tools/postgres-replication-stats --- ## About The `postgres-replication-stats` tool queries pg_stat_replication to surface the status of connected replicas. It reports application_name, client address, connection and sync state, and human-readable lag sizes (sent, write, flush, replay, and total) computed using WAL LSN differences. Compatible sources: - [alloydb-postgres](../../sources/alloydb-pg.md) - [cloud-sql-postgres](../../sources/cloud-sql-pg.md) - [postgres](../../sources/postgres.md) This tool takes no parameters. It returns a JSON array; each element represents a replication connection on the primary and includes lag metrics formatted by pg_size_pretty. ## Example ```yaml tools: replication_stats: kind: postgres-replication-stats source: postgres-source description: "Lists replication connections and readable WAL lag metrics." ``` Example response element: ```json { "pid": 12345, "usename": "replication_user", "application_name": "replica-1", "backend_xmin": "0/0", "client_addr": "10.0.0.7", "state": "streaming", "sync_state": "sync", "sent_lag": "1234 kB", "write_lag": "12 kB", "flush_lag": "0 bytes", "replay_lag": "0 bytes", "total_lag": "1234 kB" } ``` ## Reference | field | type | required | description | |------------------:|:-------:|:--------:|:------------| | pid | integer | true | Process ID of the replication backend on the primary. | | usename | string | true | Name of the user performing the replication connection. | | application_name | string | true | Name of the application (replica) connecting to the primary. | | backend_xmin | string | false | Standby's xmin horizon reported by hot_standby_feedback (may be null). | | client_addr | string | false | Client IP address of the replica (may be null). | | state | string | true | Connection state (e.g., streaming). | | sync_state | string | true | Sync state (e.g., async, sync, potential). | | sent_lag | string | true | Human-readable size difference between current WAL LSN and sent_lsn. | | write_lag | string | true | Human-readable write lag between sent_lsn and write_lsn. | | flush_lag | string | true | Human-readable flush lag between write_lsn and flush_lsn. | | replay_lag | string | true | Human-readable replay lag between flush_lsn and replay_lsn. | | total_lag | string | true | Human-readable total lag between current WAL LSN and replay_lsn. |