---
title: "All Your GUCs in a Row: commit_delay and commit_siblings"
url: https://daily.dev/posts/all-your-gucs-in-a-row-commit-delay-and-commit-siblings-ny2v6xixo
source_url: https://postgr.es/p/9kD
type: article
source: "Planet PostgreSQL"
published: 2026-05-31T07:44:53.207Z
updated: 2026-05-31T09:22:53.832Z
tags: ["backend", "postgresql"]
reading_time: 4
upvotes: 0
comments: 0
language: en
---

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# All Your GUCs in a Row: commit_delay and commit_siblings

**[Planet PostgreSQL](https://daily.dev/sources/planet-postgresql)** · 4 min read · 0 upvotes · 0 comments

## Summary

A deep dive into PostgreSQL's `commit_delay` and `commit_siblings` GUC parameters, explaining how they control group commit behavior by introducing a deliberate pause before WAL flushes to batch more transactions. The post clarifies the post-9.3 group commit mechanics, explains the correct tuning method using `pg_test_fsync` to measure flush cost, and describes how to interpret `pg_stat_wal` (or `pg_stat_io` in PG18) to confirm WAL sync is actually the bottleneck. The key insight: raise `commit_siblings` on fast storage (only batch under heavy concurrency), lower it on slow storage. For most workloads, defaults are correct, and `synchronous_commit` is a bigger lever for commit-cost savings.

## Full article

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

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Tags: [#backend](https://daily.dev/tags/backend), [#postgresql](https://daily.dev/tags/postgresql)

[View this post on daily.dev](https://daily.dev/posts/all-your-gucs-in-a-row-commit-delay-and-commit-siblings-ny2v6xixo)