--- title: All Your GUCs in a Row: io_method and io_workers | daily.dev description: A detailed breakdown of PostgreSQL 18's io_method and io_workers GUCs, which control the asynchronous I/O execution engine introduced with the new AIO... canonical: https://daily.dev/posts/all-your-gucs-in-a-row-io-method-and-io-workers-vw3i6iid7 twitter:card: summary_large_image twitter:site: @dailydotdev og:type: website og:site_name: daily.dev og:title: All Your GUCs in a Row: io_method and io_workers | daily.dev og:description: A detailed breakdown of PostgreSQL 18's io_method and io_workers GUCs, which control the asynchronous I/O execution engine introduced with the new AIO... og:url: https://daily.dev/posts/all-your-gucs-in-a-row-io-method-and-io-workers-vw3i6iid7 og:image: https://api.daily.dev/og/posts/Vw3i6Iid7.png og:image:alt: All Your GUCs in a Row: io_method and io_workers og:image:width: 1200 og:image:height: 630 og:locale: en --- > ## Documentation Index > Fetch the complete documentation index at: https://daily.dev/llms.txt > Use this file to discover all available pages before exploring further. # All Your GUCs in a Row: io_method and io_workers **[Planet PostgreSQL](https://daily.dev/sources/planet-postgresql)** · 4 min read · 0 upvotes · 0 comments ## Summary A detailed breakdown of PostgreSQL 18's io_method and io_workers GUCs, which control the asynchronous I/O execution engine introduced with the new AIO subsystem. io_method (postmaster context, requires restart) selects between sync, worker (the default, portable across platforms), and io_uring (fastest but requires --with-liburing, a current Linux kernel, and permissive seccomp policies). io_workers sizes the worker pool for worker mode; the piece corrects an earlier claim that this required a restart—it's actually sighup context and can be changed with just a reload. The default pool size of 3 is tuned for minimal hardware, and an undersized pool silently degrades to synchronous I/O rather than erroring, visible via the AioWorkerSubmissionQueue LWLock wait event in pg_stat_activity. Recommendations: use io_uring where your kernel and security policy allow it, otherwise stay on worker, and size io_workers based on observed queue contention rather than guesswork, since PostgreSQL 19 will self-size the pool. ## Full article daily.dev links to this article rather than hosting it. Read it at the original source: ## Questions this post answers ### Does changing PostgreSQL's io_workers setting require a server restart? No, io_workers has sighup context, so it can be changed with a configuration reload rather than a full restart. This corrects earlier guidance suggesting the worker pool size was fixed at boot time. The pool still won't self-size until PostgreSQL 19, but resizing it manually only costs a reload, making it cheap to experiment with different values. _Track PostgreSQL configuration nuances like this on daily.dev when tuning I/O settings without downtime._ ### What does the AioWorkerSubmissionQueue wait event mean in PostgreSQL pg_stat_activity? It indicates contention on the single cluster-wide I/O submission queue used by PostgreSQL's worker-mode async I/O, meaning the io_workers pool is too small for the load. When the queue is full or workers are behind, backends silently fall back to performing I/O synchronously themselves, without errors or logs, so this wait event climbing is the primary signal to increase io_workers. _Developers debugging silent I/O degradation can follow deep-dive database internals coverage on daily.dev._ ### What are the requirements to use io_uring as the I/O method in PostgreSQL 18? PostgreSQL must be built with --with-liburing (PGDG packages include this), running on a reasonably current Linux kernel, and under a security policy that permits io_uring, since container seccomp profiles and hardened distributions often block it. If io_uring is blocked by policy, the server fails to start entirely rather than running slowly, so testing the setting in staging first is recommended. _Compare I/O engine tradeoffs like io_uring versus worker mode on daily.dev before changing production database configs._ ## Similar posts on daily.dev - [All Your GUCs in a Row: effective\_io\_concurrency](https://daily.dev/posts/all-your-gucs-in-a-row-effective-io-concurrency-99xuwf0xm) · Planet PostgreSQL · 0 upvotes · 0 comments - [kernel asynchronous reads in PostgreSQL 19 \(io\_uring\)](https://daily.dev/posts/kernel-asynchronous-reads-in-postgresql-19-io-uring--ozzbu63ec) · Lobsters · 0 upvotes · 0 comments - [All Your GUCs in a Row: io\_max\_concurrency](https://daily.dev/posts/all-your-gucs-in-a-row-io-max-concurrency-pju4kgu6w) · Planet PostgreSQL · 0 upvotes · 0 comments - [Benchmarking Postgres 17 vs 18 — PlanetScale](https://daily.dev/posts/benchmarking-postgres-17-vs-18-planetscale-tzv6uysjb) · Hacker News · 1 upvotes · 0 comments --- Tags: [#postgresql](https://daily.dev/tags/postgresql) [View this post on daily.dev](https://daily.dev/posts/all-your-gucs-in-a-row-io-method-and-io-workers-vw3i6iid7) ```json {"@context":"https://schema.org","@graph":[{"@type":"Organization","@id":"https://daily.dev/#organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180},"sameAs":["https://twitter.com/dailydotdev","https://github.com/dailydotdev","https://www.linkedin.com/company/daily-dev-ltd"]},{"@type":"WebSite","@id":"https://daily.dev/#website","url":"https://daily.dev","name":"daily.dev","publisher":{"@id":"https://daily.dev/#organization"},"potentialAction":{"@type":"SearchAction","target":{"@type":"EntryPoint","urlTemplate":"https://daily.dev/search?q={search_term_string}"},"query-input":"required name=search_term_string"}}]} {"@context":"https://schema.org","@type":"TechArticle","headline":"All Your GUCs in a Row: io_method and io_workers","url":"https://daily.dev/posts/all-your-gucs-in-a-row-io-method-and-io-workers-vw3i6iid7","mainEntityOfPage":{"@type":"WebPage","@id":"https://daily.dev/posts/all-your-gucs-in-a-row-io-method-and-io-workers-vw3i6iid7"},"datePublished":"2026-08-14T01:01:28.339Z","dateModified":"2026-08-14T01:01:55.616Z","description":"A detailed breakdown of PostgreSQL 18's io_method and io_workers GUCs, which control the asynchronous I/O execution engine introduced with the new AIO...","image":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/64e09e83335f5a687189188d75a1ba6c?_a=AQAEuop","thumbnailUrl":"https://media.daily.dev/image/upload/f_auto,q_auto/v1/posts/64e09e83335f5a687189188d75a1ba6c?_a=AQAEuop","isAccessibleForFree":true,"articleSection":"Planet PostgreSQL","inLanguage":"en","publisher":{"@type":"Organization","name":"daily.dev","url":"https://daily.dev","logo":{"@type":"ImageObject","url":"https://daily.dev/apple-touch-icon.png","width":180,"height":180}},"author":{"@type":"Organization","name":"Planet PostgreSQL","logo":"https://media.daily.dev/image/upload/logos/placeholder.jpg","url":"https://daily.dev/sources/planet-postgresql"},"commentCount":0,"discussionUrl":"https://daily.dev/posts/all-your-gucs-in-a-row-io-method-and-io-workers-vw3i6iid7","interactionStatistic":[{"@type":"InteractionCounter","interactionType":{"@type":"LikeAction"},"userInteractionCount":0},{"@type":"InteractionCounter","interactionType":{"@type":"CommentAction"},"userInteractionCount":0}],"keywords":"postgresql","timeRequired":"PT4M"} {"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Home","item":"https://daily.dev"},{"@type":"ListItem","position":2,"name":"Planet PostgreSQL","item":"https://daily.dev/sources/planet-postgresql"},{"@type":"ListItem","position":3,"name":"All Your GUCs in a Row: io_method and io_workers"}]} {"@context":"https://schema.org","@type":"FAQPage","@id":"https://daily.dev/posts/all-your-gucs-in-a-row-io-method-and-io-workers-vw3i6iid7#faq","mainEntity":[{"@type":"Question","name":"Does changing PostgreSQL's io_workers setting require a server restart?","acceptedAnswer":{"@type":"Answer","text":"No, io_workers has sighup context, so it can be changed with a configuration reload rather than a full restart. 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