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Server response sending triggers Nagle's algorithm/delayed ACK interaction #199

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kyrias opened this issue Sep 9, 2022 · 0 comments · May be fixed by #200
Open

Server response sending triggers Nagle's algorithm/delayed ACK interaction #199

kyrias opened this issue Sep 9, 2022 · 0 comments · May be fixed by #200

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@kyrias
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kyrias commented Sep 9, 2022

The way the async-h1 encoder streams the HTTP response head and body to the given io: Write causes the head and body to be written to the underlying socket as separate calls to send, causing them to be sent as separate TCP segments.

If we're handling more than one HTTP request from the same io that means that we're doing two sends and then a read. This I/O pattern triggers a bad interaction between Nagle's algorithm and delayed ACK where the read can take up to 500 milliseconds. (On Linux this is 40 milliseconds.)

A work-around for this is to enable TCP_NODELAY to disable Nagle's algorithm, but we shouldn't really be sending undersized TCP segment unnecessarily.

kyrias added a commit to kyrias/tide that referenced this issue Sep 9, 2022
Due to the way the `async-h1` crate writes HTTP responses to the `TcpStream` the head
and body end up in separate write calls to the underlying socket.  If we're responding
to more than one request received from the same `TcpStream` it means that we did two
sends and then tried to read.  That read can take up to 500 milliseconds to complete due
to bad interactions between Nagle's algorithm and delayed ACK.  (In practice this is 40
ms on Linux.)

Disabling Nagle's algorithm works around this until `async-h1` is fixed.

http-rs/async-h1#199

Signed-off-by: Johannes Löthberg <[email protected]>
kyrias added a commit to kyrias/async-h1 that referenced this issue Dec 30, 2022
Fixes http-rs#199.

Signed-off-by: Johannes Löthberg <[email protected]>
@kyrias kyrias linked a pull request Dec 30, 2022 that will close this issue
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