perf: enable TCP_NODELAY on sockets - #4336
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Correctness: - Windows writes idle and interval together through `SIO_KEEPALIVE_VALS` and cannot leave one of them alone, so an unset one was being sent as 0 ms rather than left at the system default. Substitute libpq's own Windows values there (2h idle, 1s interval), as `pqSetKeepalivesWin32` does. - Normalize the parameters in one place, `TcpKeepalive::normalized()`: zero means "system default", and fractional durations round up to whole seconds. `socket2` truncates, so a sub-second value reached `setsockopt()` as a literal 0, which Linux rejects with `EINVAL`; only the URL parser normalized before, leaving both builders (and MySQL, which has no URL form) exposed. - A value the kernel rejects now fails with `Error::Configuration` naming the parameters instead of a bare `Io(EINVAL)` that mentions neither. - `?keepalives_idle=0` on its own left keepalive off, because 0 was folded to "unset" before deciding whether any parameter had been given. Any of the three now turns keepalive on, as in libpq. - Negative values clamp to "system default" as libpq's `strtol` path does, rather than failing to parse. - `build_url()` emits the keepalive parameters, so they survive `to_url_lossy()` alongside `sslmode` and `statement-cache-capacity`. - Raise the workspace `tokio` floor to 1.27, the first release with `AsFd`/`AsSocket` on `TcpStream`, which `SockRef::from()` requires. Docs: - Correct the platform-support paragraph: `idle` is silently dropped on OpenBSD, Haiku and Vita, and `retries` fails the connection rather than being ignored where `TCP_KEEPCNT` is missing. - List the four URL parameters in the `PgConnectOptions` table with a note on the semantics, and say on the MySQL side that no URL form exists. - Cite transact-rs#4336 for `TCP_NODELAY` rather than transact-rs#3055, which was reverted by transact-rs#4022. - Correct the socket2 dependency comment: `tokio` only bundles socket2 0.6 from 1.47 onwards. Tests: - Exercise the `setsockopt()` path on a loopback socket, reading the values back and covering the zero, sub-second and kernel-rejected cases. Only the builder and URL parsing were covered before, so none of the above was observable. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Hi @dmitryvk, many thanks for the fix; this looks more like a regression, currently with the latest version: 
But the fix makes it behave like before; I caught this while testing with (https://github.com/nbari/dbpulse/) @abonander any idea when this will be released? |
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Setting TCP_NODELAY removes unnecessary delays when sending network packets, removing ~40ms delay in some cases.
Does your PR solve an issue?
Fixes #4335
Is this a breaking change?
No, not a breaking change. This only improves performance in some cases.