perf: raise server MAX_READ_SIZE to SFTP standard 255 KiB#197
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Yaminyam wants to merge 1 commit intolablup:mainfrom
Open
perf: raise server MAX_READ_SIZE to SFTP standard 255 KiB#197Yaminyam wants to merge 1 commit intolablup:mainfrom
Yaminyam wants to merge 1 commit intolablup:mainfrom
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The bssh-server hard-capped every SFTP `READ` reply at 64 KiB (`MAX_READ_SIZE = 65536`) regardless of what the client requested. `bssh-russh-sftp` and OpenSSH's `sftp-server` both use the SFTP standard `MAX_READ_LENGTH = 261120` (255 KiB) for request sizing, so a client asking for a 256 KiB chunk only ever got 64 KiB back, forcing it to issue four extra requests for the same byte stream. Bump `MAX_READ_SIZE` to `261120` so server replies match the standard chunk size used by the rest of the stack. Combined with client-side pipelining (lablup#196), this directly cuts the per-MiB request count on downloads from 16 → 4. Memory exposure stays bounded: handles are still capped at `MAX_HANDLES = 1000` per session and each in-flight read still uses a single per-request buffer of this size (max ~255 KiB × in-flight requests).
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Summary
`bssh-server` hard-capped every SFTP `READ` reply at 64 KiB (`MAX_READ_SIZE = 65536`) regardless of what the client requested. Both `bssh-russh-sftp` and OpenSSH's `sftp-server` use the SFTP standard `MAX_READ_LENGTH = 261120` (255 KiB) for request sizing, so a client asking for a 256 KiB chunk only got 64 KiB back, forcing it to issue four extra requests for the same byte stream.
This PR bumps `MAX_READ_SIZE` to `261120` so server replies match the standard chunk size used by the rest of the stack.
Why
Combined with client-side pipelining (#196), the per-MiB request count on downloads drops from 16 → 4. Each request still pays SFTP framing + russh dispatch + tokio task hop overhead, so cutting the request count is the closest single-line lever to OpenSSH's effective per-byte cost.
Memory
Handles are still capped at `MAX_HANDLES = 1000` per session, and each in-flight read still uses a single per-request buffer of this size (max ~255 KiB × in-flight requests). Worst-case is ~16 MiB per session at 64 in-flight, well below the previous unpatched download path which buffered the full file in RSS.
Test plan