# Check PostgreSQL rewind prerequisites before modifying a former primary

> Preserve a clear fallback and verify prerequisites before rewinding a former PostgreSQL primary.

- Canonical URL: https://update.dsesecurity.com/updates/check-postgresql-rewind-prerequisites-before-modifying-a-former-primary/
- Publisher: Detection Systems & Engineering (DSE Security)
- Author: DSE Security Editorial Team
- Published: 2026-10-15T13:32:30+00:00
- Modified: 2026-10-15T13:36:15+00:00
- Last reviewed by DSE: 2026-10-15
- Resource type: Guide
- DSE priority: Information
- Topics: Business Continuity, IT
- Reading time: 2 minutes

## What you need to know

Preserve a clear fallback and verify prerequisites before rewinding a former PostgreSQL primary.

## Potentially affected

This applies to PostgreSQL 17 pg_rewind after timeline divergence. It is a rejoin procedure for a qualified administrator, not an instruction to reconnect an old primary automatically.

## DSE recommendation

DSE recommends documenting the authoritative source and preserving the former primary's stopped state before evaluating rewind.

## Article

Preserve a clear fallback and verify prerequisites before rewinding a former PostgreSQL primary.

## Source facts

PostgreSQL 17 pg_rewind requires the target cluster to have data checksums or wal_log_hints enabled, along with full_page_writes. Its dry-run option performs the work without modifying the target directory. A failure during actual rewind can leave the target directory unusable; the documentation recommends taking a fresh backup in that case. Rewind also copies configuration files from the source, so recovery configuration may need correction before the target is restarted as a standby.

Source: [PostgreSQL 17 — pg_rewind](https://www.postgresql.org/docs/17/app-pgrewind.html).

## Applicability

This applies to PostgreSQL 17 pg_rewind after timeline divergence. It is a rejoin procedure for a qualified administrator, not an instruction to reconnect an old primary automatically.

## DSE recommendation

DSE recommends documenting the authoritative source and preserving the former primary’s stopped state before evaluating rewind. Verify prerequisites and WAL availability, run the dry run, and agree on a fresh-base-backup fallback. Review copied configuration before startup, especially the settings that establish the standby role. Include a stopping condition for any uncertainty about source identity; recovery speed should not replace an explicit decision about which timeline the service will retain.

## Verification

Rehearse divergence and rejoin with disposable clusters. Record prerequisite checks, dry-run output, the actual operation’s result, and the target’s verified standby state afterward. Confirm replication resumes from the intended source and keep the tested fresh-backup fallback available if rewind cannot finish safely.

## Official reference

[PostgreSQL 17 — pg_rewind](https://www.postgresql.org/docs/17/app-pgrewind.html). Reviewed October 15, 2026.

## Primary reference

- Name: PostgreSQL 17 — pg_rewind
- Authority: www.postgresql.org
- URL: https://www.postgresql.org/docs/17/app-pgrewind.html
- Source publication date: Not stated by the source

## Citation and use

Preferred citation: “Check PostgreSQL rewind prerequisites before modifying a former primary,” DSE Security, https://update.dsesecurity.com/updates/check-postgresql-rewind-prerequisites-before-modifying-a-former-primary/
Publishing principles: https://update.dsesecurity.com/updates/dse-updates-editorial-methodology/
Usage and citation policy: https://update.dsesecurity.com/usage/
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