# ignore_system_indexes

> ignore_system_indexes — Disables reading from system indexes. Observed in PG9.0–19 Beta 3; its last measured boot default is off in PG19 Beta 3, with backend context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “Disables reading from system indexes.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `bool` | Upstream pg_settings type |
| Context | `backend` | Fixed when a backend starts |
| Unit | — | Raw unit |
| Range | — | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Developer Options | Upstream classification |
| Latest boot value | `off` | off |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG9.0 (research boundary) |
| Present in | PG9.0–19 Beta 3 |
| Removed in | No |
| Introduction commit | Not asserted: predates the PG9.0 research boundary |
| Commit date | — |
| Discussion | — |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG9.0–19 Beta 3 | `off` | — | off |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

ignore_system_indexes makes a newly started backend read system catalogs without using their indexes, while catalog modifications still update the indexes. It is intended to recover from damaged system indexes.

Because its backend context is fixed at session start, changing the setting inside an existing session is ineffective. Catalog scans can become very slow.

The mode does not repair an index; it only creates a path to inspect data and REINDEX the damaged system index. Leaving it enabled hides symptoms and imposes broad catalog overhead. Its backend context fixes the value during connection startup; an existing session cannot change it.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | Never use ignore_system_indexes as tuning or a steady-state availability setting. Stop writes, preserve immutable copies, exhaust backup/storage repair, document expected data loss, salvage narrowly, rebuild, and validate before any return to service. |
| OLAP | Read-only analytics does not make ignore_system_indexes safe: corrupted pages can still poison results or structures. Use only on a disposable salvage copy with explicit acceptance of lost data. |
| Small nodes | Do not enable ignore_system_indexes merely because no replica exists. Preserve the original first and seek a clean backup; this switch can convert visible corruption into silent loss. |
{.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: PG9.0–19 Beta 3 unmodified; OLAP: PG9.0–19 Beta 3 unmodified; CRIT: PG9.0–19 Beta 3 unmodified; TINY: PG9.0–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

## Common pitfalls {#common-pitfalls}

- Leaving ignore_system_indexes enabled after the bounded diagnostic or recovery task.
- Running the experiment on the only copy of production data.
- Underestimating log, core-file, temporary-file, WAL, CPU, or connection-slot amplification.
- Treating a server that merely starts or completes a query as proof that data and behavior are correct.

## Related parameters {#related-parameters}

[`allow_system_table_mods`](/parameters/allow-system-table-mods/) · [`ignore_checksum_failure`](/parameters/ignore-checksum-failure/) · [`zero_damaged_pages`](/parameters/zero-damaged-pages/) · [`shared_buffers`](/parameters/shared-buffers/)

## References {#references}

- [PostgreSQL 19 Beta 3 — ignore_system_indexes](https://www.postgresql.org/docs/19/runtime-config-developer.html#GUC-IGNORE-SYSTEM-INDEXES)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)