commit_delay
No restart — reload (superuser)time (microseconds)
A tiny pause before flushing WAL so concurrent commits can share one flush (group commit).
What it does
commit_delay inserts a small wait before a WAL flush, hoping other transactions commit in that window so their WAL is flushed together — amortizing the expensive sync across many commits (group commit). It only engages once at least commit_siblings (default 5) other transactions are already in their commit phase.
How to tune it
Leave it 0 unless you're explicitly tuning a high-commit-rate workload on slow fsync storage. Values that have historically helped are in the 1000–10000 µs (1–10 ms) range, and only with concurrency well above commit_siblings — always measure before/after, since on fast storage or with synchronous_commit off it just adds latency for no gain.