# hosts_file

> hosts_file — Sets the server's "hosts" configuration file. Observed in PG19 Beta 3; its last measured boot default is not set in PG19 Beta 3, with postmaster context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Sets the server's "hosts" configuration file.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `string` | Upstream pg_settings type |
| Context | `postmaster` | Requires a server restart |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | File Locations | Upstream classification |
| Latest boot value | — | not set |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG19 Beta 3 |
| Present in | PG19 Beta 3 |
| Removed in | No |
| Introduction commit | [`4f433025f666`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=4f433025f666fa4a6209f0e847715767fb1c7ace) — ssl: Serverside SNI support for libpq |
| Commit date | 2026-03-18 |
| Discussion | [thread 1](https://postgr.es/m/1C81CD0D-407E-44F9-833A-DD0331C202E5@yesql.se) |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG19 Beta 3 | — | — | not set |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

PostgreSQL describes hosts_file as follows: “Sets the server's "hosts" configuration file.” The value is fixed when the server starts, so changing it requires a controlled restart. The atlas measures it in PG19 Beta 3; boot_val is the compiled or initialized baseline, not proof of a running cluster's effective setting.

The path identifies pg_hosts.conf, the server-side SNI mapping file introduced in PostgreSQL 19. When ssl_sni is enabled, hostname, /no_sni/, and wildcard entries select certificate, key, optional CA, and optional passphrase commands; an empty or missing file falls back to the ordinary postgresql.conf TLS files.

Read it together with ssl_sni, ssl_cert_file, ssl_key_file, ssl_ca_file. Check SHOW and pg_settings on the target server, verify the source and pending_restart fields, and compare workload, logs, and resource metrics before and after any change.

## Tuning advice {#tuning-advice}

> [!TIP]
> **Advice.** These are workload-specific starting points and must be validated with measurements.

| Workload | Guidance |
| --- | --- |
| OLTP | Roll out through staged clients, validate certificate selection and expiry warnings, and monitor authentication failures. Keep a tested fallback and treat file permissions and secret rotation as part of the same change. |
| OLAP | Apply the same security policy to batch drivers and long-lived ETL connections. Test clients that omit SNI, credential-expiry automation, reload behavior, and certificate-chain compatibility. |
| Small nodes | Prefer a simple, documented TLS and credential policy. Do not enable multi-certificate routing without a test for every hostname and fallback path, and never weaken verification to hide configuration mistakes. |
{.full-width}

## Pigsty {#pigsty}

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG19 Beta 3; this does not assert current Pigsty support for that historical or beta release.

| Template | Effective value | Versus upstream boot | Source expression |
| --- | --- | --- | --- |
| OLTP | Unmodified | — | — |
| OLAP | Unmodified | — | — |
| CRIT | Unmodified | — | — |
| TINY | Unmodified | — | — |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG19 Beta 3 unmodified; OLAP: PG19 Beta 3 unmodified; CRIT: PG19 Beta 3 unmodified; TINY: PG19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Treating the measured boot_val for hosts_file as proof of the effective value on an initialized or managed cluster.
- Applying a change as though it were immediate while pg_settings reports postmaster context.
- Changing this setting in isolation without checking the linked limits, observability, and rollback path.
- Depending on beta behavior in production without retesting the PostgreSQL 19 final release.

## Related parameters {#related-parameters}

[`ssl_sni`](/parameters/ssl-sni/) · [`ssl_cert_file`](/parameters/ssl-cert-file/) · [`ssl_key_file`](/parameters/ssl-key-file/) · [`ssl_ca_file`](/parameters/ssl-ca-file/) · [`hba_file`](/parameters/hba-file/)

## References {#references}

- [PostgreSQL 19 Beta 3 — hosts_file](https://www.postgresql.org/docs/19/runtime-config-file-locations.html#GUC-HOSTS-FILE)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)