# Replication Monitor

> Monitors database replication health (streaming, logical, multi-region) and diagnoses lag, conflicts, and failover readiness.

- Skill: `uitbreidenos/replication-monitor` (Agent Skill)
- Install (CLI): `npx skillmds@latest add uitbreidenos/replication-monitor`
- Raw SKILL.md: https://api.skillmd.com/api/skills/uitbreidenos/replication-monitor/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: UitbreidenOS (https://skillmd.com/u/uitbreidenos)
- Updated: 2026-09-22
- Page: https://skillmd.com/skills/uitbreidenos/replication-monitor

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# Replication Monitor

## When to activate
When replication lag exceeds acceptable thresholds, during failover testing, when setting up new replicas, or during routine weekly health checks.

## When NOT to use
Skip if replication lag is under 1 second and all replicas report healthy. Skip for single-node development databases.

## Instructions

1. Check replication status: `pg_stat_replication` for PostgreSQL, `SHOW REPLICA STATUS` for MySQL.
2. Measure lag: write lag (sent vs flush), replay lag (flush vs replay), byte lag.
3. Identify lag sources: large transactions, DDL operations, network saturation, disk I/O on replica.
4. Test failover: simulate primary failure, measure time-to-promote, verify data consistency.
5. Check for replication conflicts: long-running reads blocking WAL apply, hot standby feedback issues.

## Example

```
REPLICATION STATUS: prod-primary → 2 replicas

Replica: prod-replica-1 (us-east-1)
  State: streaming ✅
  Write lag: 120ms | Replay lag: 180ms
  Byte lag: 2.4MB
  Conflicts: 0

Replica: prod-replica-2 (us-west-2)
  State: streaming ✅
  Write lag: 450ms | Replay lag: 620ms    ⚠️
  Byte lag: 18MB
  Conflicts: 3 (long-running analytics queries)

Action: Cancel 3 conflicting queries on replica-2 or increase
        max_standby_streaming_delay to 30s.
```