influxdata/influxdb · error · Error

IO error

Error message

IO error: {0}

What it means

serialize::Error::Io wraps a std::io::Error encountered while reading a WAL file (via #[from]). The serializer reads the file bytes before parsing; any filesystem-level failure — permission denied, file missing mid-read, I/O errors from the disk — surfaces as this variant with the OS error message embedded.

Solutions

1. Check file permissions and ownership on the WAL directory/files (the inner io::Error kind will say PermissionDenied).
2. Re-run after fixing the transient storage issue (remount, disk replacement); replay is idempotent up to the failure point.
3. Exclude the WAL directory from aggressive cleanup jobs that race with the reader.
4. Look at the wrapped io::Error message to distinguish not-found vs permission vs hardware error and fix accordingly.

Example fix

# before
sudo -u otheruser influxdb3 ...   # Io(Os { code: 13, kind: PermissionDenied })
# after: run the reader as the WAL directory owner
sudo -u influxdb3 influxdb3 ...

// check readability of every WAL file before replay
fn readable(path: &Path) -> bool {
    std::fs::File::open(path).and_then(|f| f.metadata()).is_ok()
}

match verify_file_type_and_deserialize(&bytes) {
    Err(serialize::Error::Io(e)) if e.kind() == std::io::ErrorKind::PermissionDenied => {
        // fix ownership/permissions, then retry replay
    }
    other => other?,
}

When it happens

Trigger: Reading a WAL file during replay/verify when the file is unreadable: wrong permissions, deleted between listing and read, disk I/O error, or a device failure while streaming bytes into verify_file_type_and_deserialize.

Common situations: WAL directory owned by a different user after running under two service accounts; NFS/network mounts dropping; EIO on failing disks; a cleanup job deleting files while the reader scans the directory.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

• error writing wal file
• io error
• tempfile i/o
• another process has written to the WAL ahead of this one
• bitcode error

AI-assisted analysis of influxdata/influxdb@06200ef96b (2026-09-19). Data as JSON: /api/errors/9858c2325136c946. Report an issue: GitHub.

Appendix: source

Thrown at influxdb3_wal/src/serialize.rs:26

use std::io::Cursor;
use std::mem::size_of;
use thiserror::Error;

#[derive(Debug, Error)]
pub enum Error {
    #[error("Invalid wal file identifier")]
    InvalidWalFile,

    #[error("WAL file too small: expected at least {expected} bytes, but got {actual} bytes")]
    WalFileTooSmall { expected: usize, actual: usize },

    #[error("crc32 checksum mismatch")]
    Crc32Mismatch,

    #[error("bitcode error: {0}")]
    Bitcode(#[from] bitcode::Error),

    #[error("IO error: {0}")]
    Io(#[from] std::io::Error),

    #[error("try from slice error {0}")]
    TryFromSlice(#[from] std::array::TryFromSliceError),
}

pub(crate) type Result<T, E = Error> = std::result::Result<T, E>;

/// The first bytes written into a wal file to identify it and its version.
const FILE_TYPE_IDENTIFIER: &[u8] = b"idb3.001";

#[inline(always)]
pub fn verify_file_type_and_deserialize(b: Bytes) -> Result<WalContents> {
    let contents = b.to_vec();

    let pos = FILE_TYPE_IDENTIFIER.len();
    const CHECKSUM_LEN: usize = size_of::<u32>();
    let min_file_size = pos + CHECKSUM_LEN;

View on GitHub (pinned to 06200ef96b)