simple_wal

A simple Rust write-ahead-logging crate.

Features

• Optimized for sequential reads & writes
• Easy atomic log compaction
• Advisory locking
• CRC32 checksums
• Range scans
• Persistent log entry index

lib.rs:

A simple write-ahead-logging crate.

Features

• Optimized for sequential reads & writes
• Easy atomic log compaction
• Advisory locking
• CRC32 checksums
• Range scans
• Persistent log entry index

The entire log is scanned through on startup in order to detect & clean interrupted writes and determine the length of the log. It's recommended to compact the log when old entries are no longer likely to be used.

Usage:

use simple_wal::LogFile;

let path = std::path::Path::new("./wal-log");

{
    let mut log = LogFile::open(path).unwrap();

    // write to log
    log.write(&mut b"log entry".to_vec()).unwrap();
    log.write(&mut b"foobar".to_vec()).unwrap();
    log.write(&mut b"123".to_vec()).unwrap();
   
    // flush to disk
    log.flush().unwrap();
}

{
    let mut log = LogFile::open(path).unwrap();

    // Iterate through the log
    let mut iter = log.iter(..).unwrap();
    assert_eq!(iter.next().unwrap().unwrap(), b"log entry".to_vec());
    assert_eq!(iter.next().unwrap().unwrap(), b"foobar".to_vec());
    assert_eq!(iter.next().unwrap().unwrap(), b"123".to_vec());
    assert!(iter.next().is_none());
}

{
    let mut log = LogFile::open(path).unwrap();

    // Compact the log
    log.compact(1).unwrap();

    // Iterate through the log
    let mut iter = log.iter(..).unwrap();
    assert_eq!(iter.next().unwrap().unwrap(), b"foobar".to_vec());
    assert_eq!(iter.next().unwrap().unwrap(), b"123".to_vec());
    assert!(iter.next().is_none());
}

Log Format:

00 01 02 03 04 05 06 07|08 09 10 11 12 13 14 15|.......|-4 -3 -2 -1|
-----------------------|-----------------------|-------|-----------|
starting index         |entry length           | entry | crc32     |
unsigned 64 bit int le |unsigned 64 bit int le | data  | 32bit, le |

Numbers are stored in little-endian format.

The first 8 bytes in the WAL is the starting index.

Each entry follows the following format:

1. A 64 bit unsigned int for the entry size.
2. The entry data
3. A 32 bit crc32 checksum.