# maintenance_io_concurrency

> maintenance_io_concurrency — A variant of "effective_io_concurrency" that is used for maintenance work. Observed in PG13–19 Beta 3; its last measured boot default is 16 in PG19 Beta 3, with user context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.
---

> [!NOTE]
> **Fact — official short description:** “A variant of "effective_io_concurrency" that is used for maintenance work.”

## Identity {#identity}

| Field | Value | Meaning |
| --- | --- | --- |
| Type | `integer` | Upstream pg_settings type |
| Context | `user` | Settable by an ordinary user |
| Unit | — | Raw unit |
| Range | `0` – `1000` | Raw limits in the last observed version |
| Enum values | — | — for non-enum types |
| Category | Resource Usage / I/O | Upstream classification |
| Latest boot value | `16` | 16 |
{.fields meta="-"}

## Lifecycle {#lifecycle}

| Fact | Value |
| --- | --- |
| First observed | PG13 |
| Present in | PG13–19 Beta 3 |
| Removed in | No |
| Introduction commit | [`fc34b0d9de27`](https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=fc34b0d9de27ab5ac2887da00b3892bdabd89e45) — Introduce a maintenance_io_concurrency setting. |
| Commit date | 2020-03-16 |
| Discussion | [thread 1](https://postgr.es/m/CA%2BhUKGJUw08dPs_3EUcdO6M90GnjofPYrWp4YSLaBkgYwS-AqA%40mail.gmail.com) |

## Default history {#default-history}

| Versions | Raw `boot_val` | Unit | Human value |
| --- | --- | --- | --- |
| PG13–17 | `10` | — | 10 |
| PG18–19 Beta 3 | `16` | — | 16 |
{.full-width caption="Measured PG9.0–19 Beta 3 boot defaults"}

## How it works {#mechanism}

maintenance_io_concurrency is the per-maintenance-operation target for storage concurrency used by work performed on behalf of many clients. A tablespace option of the same name can override it for that storage; it is neither a cluster-wide device cap nor a memory allocation.

In PG13–17 it chiefly controls maintenance prefetch on supported systems. The measured Linux-Docker boot value is 10, while unsupported platforms without effective prefetch-advice support defaulted to 0; those releases do not have the PG18 core-AIO execution model.

PostgreSQL 18 integrates the target with core AIO and uses a boot default of 16. io_max_concurrency separately clamps simultaneous execution by one process, io_method chooses the execution mechanism, and combine limits control bytes per request. Its user context permits scoped runtime changes.

## Tuning advice {#tuning-advice}

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

| Workload | Guidance |
| --- | --- |
| OLTP | For PG13–17, tune this as a maintenance-prefetch target only on supported storage; for PG18, tune it as an AIO concurrency target. Measure foreground tail latency while VACUUM or other eligible maintenance runs, and use a tablespace override for heterogeneous storage. |
| OLAP | Higher maintenance concurrency can shorten eligible scans or vacuum work on high-latency, high-IOPS storage, but it can also deepen the queue seen by analytical queries. Benchmark maintenance completion time and mixed-workload latency together; it does not change request size. |
| Small nodes | Use the version- and platform-appropriate default unless maintenance is demonstrably I/O-stalled. A small host can saturate storage with a low target, so do not copy Pigsty's SSD value 100 without measurement. |
{.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 | `100` | different | `100` |
| OLAP | `100` | different | `100` |
| CRIT | `100` | different | `100` |
| TINY | `100` | different | `100` |
{.full-width}

> [!CAUTION]
> **Advice — pending human review.** Fact from the current Pigsty template projection: OLTP: PG13–19 Beta 3 = 100 (dcs); OLAP: PG13–19 Beta 3 = 100 (dcs); CRIT: PG13–19 Beta 3 = 100 (dcs); TINY: PG13–19 Beta 3 = 100 (dcs). Advice, pending human review — Editorial inference: the template asks SSD maintenance to exploit more prefetch/AIO concurrency, but the value is a target per maintenance operation and must be validated against foreground latency.

## Common pitfalls {#common-pitfalls}

- Calling 10 the unconditional PG13–17 default when unsupported platforms used 0.
- Back-projecting PG18 core-AIO semantics into PG13–17 prefetch behavior.
- Treating the per-operation target as a cluster or device-wide cap.
- Confusing concurrency with io_combine_limit's bytes-per-request dimension.
- Using one value across tablespaces with materially different storage.

## Related parameters {#related-parameters}

[`effective_io_concurrency`](/parameters/effective-io-concurrency/) · [`io_method`](/parameters/io-method/) · [`io_max_concurrency`](/parameters/io-max-concurrency/) · [`io_combine_limit`](/parameters/io-combine-limit/) · [`vacuum_buffer_usage_limit`](/parameters/vacuum-buffer-usage-limit/)

## References {#references}

- [PostgreSQL 19 Beta 3 — maintenance_io_concurrency](https://www.postgresql.org/docs/19/runtime-config-resource.html#GUC-MAINTENANCE-IO-CONCURRENCY)
- [PostgreSQL 19 release notes](https://www.postgresql.org/docs/19/release-19.html)
- [Machine-readable GUC export](/data/guc.jsonl)