Measure your WAL generation rate
pg_current_wal_lsn plus pg_wal_lsn_diff lets you measure exactly how much WAL a workload produces. Here 200,000 inserts generated 30 MB of WAL, the number that drives archiving, replication, and disk planning.
Problem
What you're actually looking at
The symptom as it shows up on a real server.
WAL volume drives replication bandwidth, archive storage, and pg_wal disk sizing, but it is invisible unless you measure it. Capturing the LSN before and after a workload and taking the difference gives you the exact bytes written.
Meridian wants to size WAL archiving and replication for a bulk-load pattern. Measuring the LSN delta across a 200,000-row insert gives a concrete WAL-per-operation figure to plan from.
Simple terms
WAL is the write-ahead log every change is recorded in, and its volume drives your replication bandwidth, your archive storage, and how big pg_wal needs to be, yet it is invisible unless you measure it. PostgreSQL exposes the current log position (the LSN); capture it before and after a workload, take the difference, and you have the exact number of bytes that workload wrote. That concrete figure is what you plan capacity from, instead of guessing.
Full runbook for this incident
- The full identify checklist, the exact signals that tell you it's this incident
- Every diagnostic query; lab output is attached only to the steps we actually captured
- The resolution path and the pitfalls that make it worse
- Mitigation steps to stop it recurring, plus a verify-you're-done query
Card required. Cancel before day 7 and you are not charged.
More in this category
Other WAL & replication runbooks
Neighbouring incidents that share the same diagnostic surface.
Need the full procedure?
Pro runbooks finish the incident path
Free runbooks teach the shape. Pro opens the full step transcript, edge cases, and prevention depth.