dj456119/AlfheimDB-WAL

The AlfheimDB's high performance write-ahead log.

AlfheimDB-WAL

A high performance write-ahead log.

Example

AlfheimDB-WAL-Example

Core Struct

 WAL file struct in storage:  
 ┌───────────┬───────────┐  
 │ 1K header │   logs    │  
 └───────────┴───────────┘  
 The file header struct:  
 ┌───────────────┬─────────────────────────────┐  
 │ Length 8Bytes │             Data            │  
 └───────────────┴─────────────────────────────┘  
 The log item struct:  
 ┌───────────────┬──────────────┬─────────────────────────────────┐  
 │ Length 8Bytes │ Index 8Bytes │              Data               │  
 └───────────────┴──────────────┴─────────────────────────────────┘  

Truncate Func

Case 1

 The log min index is 5, max index is 13
 If start in (-,5] && end in [13,-)
 Need truncate all log, so we remove this file
 ┌─┬─┬─┬─┬─┬──┬──┬──┬──┐
 │5│6│7│8│9│10│11│12│13│
 └─┴─┴─┴─┴─┴──┴──┴──┴──┘

Case 2

 The log min index is 5, max index is 13
 If start in [5,13) && end in [13,-)
 Need truncate from start to last log
 ┌─┬─┬─┬─┬─┬──┬──┬──┬──┐
 │5│6│7│8│9│10│11│12│13│
 └─┴─┴─┴─┴─┴──┴──┴──┴──┘

Case 3

 The log min index is 5, max index is 13
 If start in (-,5] && end in [5,13]
 Need truncate from the first log to end
 Put these pos into TruncateArea
 ┌─┬─┬─┬─┬─┬──┬──┬──┬──┐
 │5│6│7│8│9│10│11│12│13│
 └─┴─┴─┴─┴─┴──┴──┴──┴──┘

Case 4

 The log min index is 5, max index is 13
 If start in [5,13] && end in [5,13]
 Need truncate from start to end
 Put these pos into TruncateArea
 ┌─┬─┬─┬─┬─┬──┬──┬──┬──┐
 │5│6│7│8│9│10│11│12│13│
 └─┴─┴─┴─┴─┴──┴──┴──┴──┘

Benchmarks

MACBOOK PRO 2020 M1 SSD

BatchWrite: 100bytes, 200 logs, loop 10000 1.6s

CENTOS 7 8C8G HDD

BatchWrite: 100bytes, 200 logs, loop 10000 5.6s