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Akka.IO: wire akka.io.tcp.maximum-frame-size to the pipe segment size (#8657) - #8663
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Aaronontheweb merged 3 commits intoSep 29, 2026
Merged
Aaronontheweb merged 3 commits into
Aaronontheweb merged 3 commits into
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…akkadotnet#8657) akkadotnet#8132 moved TCP onto System.IO.Pipelines, and maximum-frame-size stopped doing anything: the pipe's default 4 KB segment size decided the read chunk and bytes-per-send instead. Pass it as minimumSegmentSize on both pipes so raising the setting cuts socket sends for large writes again, restoring the v1.5 behavior. Also fixes the TcpSettings buffer-size exception messages, which said "at least 2x the maximum frame size" while the check is 1x.
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This was referenced Sep 29, 2026
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Closes #8657.
akka.io.tcp.maximum-frame-size(TcpSettings.MaxFrameSizeBytes) capped the read buffer and the bytes per socket send in v1.5. It has done nothing since #8132 moved Akka.IO TCP onto System.IO.Pipelines. The pipes' default 4 KB segments took its place, because the write pump sends one segment perWriteAsyncand each read fills one segment. The default behavior happened to match (4k), but raising the setting silently stopped working. No release includes #8132, so this is a v1.6 regression.Changes
minimumSegmentSize: settings.MaxFrameSizeBytes. WithInet.SO.PipeBufferSizeset, the output pipe's watermarks are 2x/1x as before; otherwise pause 64 KB, resume 32 KB, the same asPipeOptions.Default.maximum-frame-sizemust now be positive (0 would make every pipe write throw); the check was< 0.TcpSettingserror messages said "at least 2x" while the check is 1x. The messages now describe the 1x check, which is unchanged. Theakka.confadvice to size the buffers at 2x the frame size stays: at 2x the kernel can hold one send while the next is copied in.akka.confcomment says what the setting does: an upper bound on bytes per socket read and per socket send, rounded up to a power of two (the pipe's pool rounds segment sizes), and each connection holds at least one buffer of that size.The default is unchanged (4 KB), so nothing changes unless someone raised the setting. It restores v1.5 behavior, so there's no ledger row.
Tests
TcpMaximumFrameSizeSpec: a single 64 KiB write reaches the socket as 16 × 4 KiB sends at the default, and as one send withmaximum-frame-size = 64k. With the fix reverted, the 64k case fails (16 × 4096). TheAkka.Tests.IOand Streams TCP suites pass.