[−][src]Crate simple_wal
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:
- A 64 bit unsigned int for the entry size.
- The entry data
- A 32 bit crc32 checksum.
Structs
LogEntry | An entry in the log. |
LogFile | A write-ahead-log. |
LogIterator |
Enums
LogError |