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+# PostgreSQL WAL Corruption Recovery Guide
+
+## Symptoms
+
+PostgreSQL container crashes on startup with logs showing:
+
+```
+LOG:  unexpected pageaddr X/Y in WAL segment ...
+LOG:  invalid checkpoint record
+PANIC:  could not locate a valid checkpoint record at ...
+LOG:  startup process (PID N) was terminated by signal 6: Aborted
+LOG:  aborting startup due to startup process failure
+```
+
+The container restarts repeatedly, each time hitting the same error.
+
+## Cause
+
+The Write-Ahead Log (WAL) was corrupted by an unclean shutdown (power loss, host crash, force kill, etc.). PostgreSQL cannot find a valid checkpoint to resume from.
+
+## What You Risk Losing
+
+- **Committed data**: Safe. It is already written to the data files.
+- **Uncommitted transactions** from the moment of the crash: Lost. These were only in WAL.
+- **Recent changes** that were committed but not yet checkpointed: Usually safe, but there is a small risk of inconsistency.
+
+## Recovery Procedure
+
+### 1. Stop the Crashing Container
+
+```bash
+cd /path/to/postgres/service
+docker compose down
+```
+
+### 2. Run `pg_resetwal`
+
+This resets the WAL and forces a clean start.
+
+**If your data is in a named Docker volume (e.g., `pgdata`):**
+
+```bash
+docker run --rm \
+  -v pgdata:/var/lib/postgresql \
+  --user postgres \
+  postgres:18 \
+  pg_resetwal -f /var/lib/postgresql/18/docker
+```
+
+> Adjust the path `/var/lib/postgresql/18/docker` to match your `PGDATA` setting.
+
+**If your data is in a bind mount (e.g., `./data`):**
+
+```bash
+docker run --rm \
+  -v $(pwd)/data:/var/lib/postgresql/data \
+  --user postgres \
+  postgres:18 \
+  pg_resetwal -f /var/lib/postgresql/data
+```
+
+### 3. Start the Database
+
+```bash
+docker compose up -d
+```
+
+### 4. Verify
+
+```bash
+docker compose logs --tail=20
+docker inspect --format='{{.State.Health.Status}}' postgres
+```
+
+You should see:
+
+```
+LOG:  database system is ready to accept connections
+```
+
+And the health status should be `healthy`.
+
+## Prevention
+
+- Ensure graceful shutdowns: `docker compose down` instead of `docker kill`
+- Use a UPS if running on bare metal to avoid power-loss crashes
+- Keep backups of important data volumes
+- Consider setting `restart: unless-stopped` instead of `always` to prevent rapid crash loops
+
+## When NOT to Use This Fix
+
+Do **not** use `pg_resetwal` if:
+- You have a recent base backup and WAL archive — restore from backup instead
+- You suspect data file corruption (not just WAL corruption)
+- You can recover by other means (e.g., starting from a replication standby)
+
+If unsure, copy the data directory somewhere safe before running `pg_resetwal`.
+
+## One-Liner for Future Emergencies
+
+If you're sure it's WAL corruption and you know your setup:
+
+```bash
+docker compose down && \
+docker run --rm -v pgdata:/var/lib/postgresql --user postgres postgres:18 pg_resetwal -f /var/lib/postgresql/18/docker && \
+docker compose up -d
+```