---
title: "All Your GUCs in a Row: effective_io_concurrency"
url: https://daily.dev/posts/all-your-gucs-in-a-row-effective-io-concurrency-99xuwf0xm
source_url: https://postgr.es/p/9mD
type: article
source: "Planet PostgreSQL"
published: 2026-06-22T01:04:22.268Z
updated: 2026-06-22T01:04:46.506Z
tags: ["postgresql"]
reading_time: 5
upvotes: 0
comments: 0
language: en
---

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# All Your GUCs in a Row: effective_io_concurrency

**[Planet PostgreSQL](https://daily.dev/sources/planet-postgresql)** · 5 min read · 0 upvotes · 0 comments

## Summary

A deep historical analysis of PostgreSQL's `effective_io_concurrency` parameter, which has changed its meaning three times across major versions. Before PostgreSQL 13, the value was fed through a harmonic-series formula tied to spindle counts. PostgreSQL 13 made it a direct I/O request count. PostgreSQL 18 transformed it again into a real async I/O depth control, backed by a new AIO subsystem with `io_method` options including `worker` and `io_uring`. The default jumped from 1 to 16 in PG18 to reflect genuine async read-ahead capability. Practical guidance: use 16+ on NVMe/cloud storage in PG18, ~200 for SSDs in PG13-17, and never copy a value across major versions without checking which era applies.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://postgr.es/p/9mD>

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