Build a Commit Log Prototype

Distributed Services with Go — by Travis Jeffery (11 / 84)

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We’ll explore commit logs in depth in Chapter 3, ​Write a Log Package​, when we build a persisted commit log library. For now, all you need to know about commit logs is that they’re a data structure for an append-only sequence of records, ordered by time, and you can build a simple commit log with a slice.

Create an internal/server directory tree in the root of your project and put the following code under the server directory in a file called log.go:

LetsGo/internal/server/log.go

​ ​package​ server
​ 
​ ​import​ (
​         ​"fmt"​
​         ​"sync"​
​ )
​ 
​ ​type​ Log ​struct​ {
​         mu      sync.Mutex
​         records []Record
​ }
​ 
​ ​func​ NewLog() *Log {
​         ​return​ &Log{}
​ }
​ 
​ ​func​ (c *Log) Append(record Record) (​uint64​, ​error​) {
​         c.mu.Lock()
​         ​defer​ c.mu.Unlock()
​         record.Offset = ​uint64​(len(c.records))
​         c.records = append(c.records, record)
​         ​return​ record.Offset, nil
​ }
​ 
​ ​func​ (c *Log) Read(offset ​uint64​) (Record, ​error​) {
​         c.mu.Lock()
​         ​defer​ c.mu.Unlock()
​         ​if​ offset >= ​uint64​(len(c.records)) {
​                 ​return​ Record{}, ErrOffsetNotFound
​         }
​         ​return​ c.records[offset], nil
​ }
​ 
​ ​type​ Record ​struct​ {
​         Value  []​byte​ ​`json:"value"`​
​…