fix: default Postgres to io_method=worker instead of io_uring

[otavio]

Description

We ship the Postgres service with io_method=io_uring forced on, plus seccomp=unconfined to allow the io_uring syscalls. On some hosts Postgres fails to start with:

could not setup io_uring queue: Cannot allocate memory

This ENOMEM from io_uring_setup is not a lack of RAM. The io_uring rings count against the container's RLIMIT_MEMLOCK, and some kernels ship with io_uring disabled via sysctl (kernel.io_uring_disabled=2, now a default on several hardened distros). Either condition makes the syscall fail regardless of how much memory the box has. io_uring is a fragile default for a self-hosted product that runs on arbitrary kernels and container runtimes.

Changes

Switch the default to Postgres 18's own default io_method=worker (asynchronous I/O via worker processes, no io_uring syscalls) in both docker-compose.postgres.yml and docker-compose.postgres.test.yml. This also removes the need for the security_opt: seccomp=unconfined override, a security downgrade carried only to enable io_uring. The performance difference from io_uring is marginal for our workload and does not justify the support burden.

Related

Fixes #6629
Reported by a self-hoster upgrading to v0.26.0 (#6627).

[github-actions]

Claude finished @otavio's task in 54s —— View job

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Code Review Complete

Reviewed 2 files across code quality, security, testing, language patterns, and architecture — no new issues found. The code looks good as-is.

A few confirming notes on the change:

• io_method=worker is a valid value for Postgres 18 and is in fact PG18's built-in default, so the flag is now effectively explicit-documentation of the default behavior — safe.
• Removing security_opt: seccomp=unconfined is a net security improvement: it restores Docker's default seccomp profile, and it was only ever added to permit the io_uring syscalls.
• Both docker-compose.postgres.yml and docker-compose.postgres.test.yml are updated consistently, and no dangling io_uring/seccomp references remain elsewhere in the repo.

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