What causes "failed to write whole buffer" in spacejam/sled?

Free disk space or raise quota, then retry the operation

failed to write whole buffer

Error message

failed to write whole buffer

What it means

write_all_at retries pwrite-like writes until the whole buffer is flushed; if the underlying write returns 0 bytes written, progress is impossible, so it returns WriteZero with this message. It indicates the storage layer accepted the call but wrote nothing.

Solutions

Free disk space or raise quota, then retry the operation
Check application logs for errors on the file handle; reopen the database if the fd went bad
Check the storage mount health (dmesg, filesystem errors) and replace failing media
Ensure no other code path closes the database file concurrently

Defensive patterns

Strategy: retry

Validate before calling

// check free space before heavy write sessions
let stat = nix::sys::statvfs::stat(path)?;
if stat.blocks_available < min_free_blocks { return Err(anyhow!("disk almost full")); }

Try / catch

match Db::open(&path) {
    Ok(db) => db,
    Err(e) if e.kind() == std::io::ErrorKind::WriteZero => {
        // free space / check fd validity, then reopen
        free_disk_or_alert()?;
        Db::open(&path)?
    }
    Err(e) => return Err(e.into()),
}

Prevention

Alert on disk usage thresholds before writes start failing
Avoid closing the database file while other handles are in use
Prefer local filesystems over flaky network mounts for database storage
Watch kernel logs for I/O errors on the backing device

When it happens

Trigger: A seek_write to the file returns Ok(0): typically a full disk, a closed/invalid file descriptor, quota exhaustion, or an I/O layer bug that reports zero-length writes.

Common situations: Disk or quota full during heavy writes; writing after the file was closed elsewhere; faulty network filesystems or FUSE mounts returning zero writes.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

AI-assisted analysis of spacejam/sled@e449d17111 (2026-09-12). Data as JSON: /api/errors/9408b391dc4b332e. Report an issue: GitHub.

Appendix: source

Thrown at src/heap.rs:482

        if !buf.is_empty() {
            Err(annotate!(io::Error::new(
                io::ErrorKind::UnexpectedEof,
                "failed to fill whole buffer"
            )))
        } else {
            Ok(())
        }
    }

    pub(super) fn write_all_at(
        file: &fs::File,
        mut buf: &[u8],
        mut offset: u64,
    ) -> io::Result<()> {
        while !buf.is_empty() {
            match maybe!(file.seek_write(buf, offset)) {
                Ok(0) => {
                    return Err(annotate!(io::Error::new(
                        io::ErrorKind::WriteZero,
                        "failed to write whole buffer",
                    )));
                }
                Ok(n) => {
                    buf = &buf[n..];
                    offset += n as u64;
                }
                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
                Err(e) => return Err(annotate!(e)),
            }
        }
        Ok(())
    }
}

#[derive(Debug)]
struct Slab {

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