手撸golang GO与微服务 Saga模式之4

2021-03-14 本文已影响0人老罗话编程

缘起

最近阅读<<Go微服务实战>> (刘金亮, 2021.1)
本系列笔记拟采用golang练习之

Saga模式

saga模式将分布式长事务切分为一系列独立短事务
每个短事务是可通过补偿动作进行撤销的
事务动作和补动作偿都是幂等的, 允许重复执行而不会有副作用

Saga由一系列的子事务“Ti”组成，
每个Ti都有对应的补偿“Ci”，
当Ti出现问题时Ci用于处理Ti执行带来的问题。

可以通过下面的两个公式理解Saga模式。
T = T1 T2 … Tn
T = TCT

Saga模式的核心理念是避免使用长期持有锁（如14.2.2节介绍的两阶段提交）的长事务，
而应该将事务切分为一组按序依次提交的短事务，
Saga模式满足ACD（原子性、一致性、持久性）特征。

摘自 <<Go微服务实战>> 刘金亮, 2021.1

目标

为实现saga模式的分布式事务, 先撸一个pub/sub事务消息队列服务
事务消息队列服务的功能性要求
- 消息不会丢失: 消息的持久化
- 消息的唯一性: 要求每个消息有全局ID和子事务ID
- 确保投递成功: 投递队列持久化, 投递状态持久化, 失败重试

子目标(Day 4)

完善投递worker
- 未处理消息: 标记, 并尝试投递
- 已处理消息: 判断是否超时, 并重试投递
- 投递成功: 移动到成功投递表
- 投递失败: 重置标记, 下轮重试
数据库表相应的细节调整
- delivery_queue: 去掉failed_count, 增加update_time时间戳
- success_queue: 去掉sub_id, 改为client_id, 并增加create_time时间戳
- failed_queue: 因为不允许失败, 因此删除失败投递表

tDeliveryWorker.go

完善投递worker
- 未处理消息: 标记, 并尝试投递
- 已处理消息: 判断是否超时, 并重试投递
- 投递成功: 移动到成功投递表
- 投递失败: 重置标记, 下轮重试

package delivery

import (
    "bytes"
    "encoding/json"
    "errors"
    "github.com/jmoiron/sqlx"
    "io/ioutil"
    "learning/gooop/saga/mqs/database"
    "learning/gooop/saga/mqs/logger"
    "learning/gooop/saga/mqs/models"
    "net/http"
    "time"
)

type tDeliveryWorker struct {
    info *tWorkerInfo
}

func newDeliveryWorker(info *tWorkerInfo) *tDeliveryWorker {
    it := new(tDeliveryWorker)
    it.info = info
    go it.beginMainLoop()
    return it
}

func (me *tDeliveryWorker) beginMainLoop() {
    for !me.isExpired() {
        ok, msg := me.peek()
        if ok {
            switch msg.StatusFlag {
            case 0:
                // 未处理的消息
                me.handleUndeliveredMsg(msg)
                break

            case 1:
                // 处理中的消息
                me.handleDeliveringMsg(msg)
                break
            }

        } else {
            time.Sleep(time.Duration(1) * time.Second)
        }
    }
}


func (me *tDeliveryWorker) isExpired() bool {
    return time.Now().UnixNano() >= me.info.ExpireTime
}

// peek: 从待投递队列中获取最早的一条记录
func (me *tDeliveryWorker) peek() (bool, *models.QueuedMsg) {
    msg := &models.QueuedMsg{}
    e := database.DB(func(db *sqlx.DB) error {
        rows, err := db.Queryx(
            "select * from delivery_queue where client_id=? order by create_time asc limit 1",
            me.info.ClientID,
        )
        if err != nil {
            return err
        }

        if rows.Next() {
            err = rows.StructScan(msg)
            if err != nil {
                return err
            }
            return nil

        } else {
            return gEmptyRowsErr
        }
    })

    if e != nil {
        return false, nil
    } else {
        return true, msg
    }
}


// handleUndeliveredMsg: if msg unhandled, then try to deliver it
func (me *tDeliveryWorker) handleUndeliveredMsg(msg *models.QueuedMsg) {
    err := database.DB(func(db *sqlx.DB) error {
        now := time.Now().UnixNano()
        r,e := db.Exec(
            "update delivery_queue set status_flag=1, update_time=? where id=? and status_flag=0 and update_time=?",
            now,
            msg.ID,
            msg.UpdateTime,
        )
        if e != nil {
            return e
        }

        rows, e := r.RowsAffected()
        if e != nil {
            return e
        }
        if rows != 1 {
            return gOneRowsErr
        }

        msg.UpdateTime = now
        return nil
    })

    if err != nil {
        logger.Logf("tDeliveryWorker.handleNewMsg, id=%v, msg=%s/%s, err=%s", me.info.ClientID, msg.GlobalID, msg.SubID, err.Error())
        return
    }

    if me.deliver(msg) {
        me.afterDeliverySuccess(msg)

    } else {
        me.afterDeliveryFailed(msg)
    }
}

// deliver: use http.Post function to delivery msg
func (me *tDeliveryWorker) deliver(msg *models.QueuedMsg) bool {
    t := &models.TxMsg{
        GlobalID: msg.GlobalID,
        SubID: msg.SubID,
        Topic: msg.Topic,
        CreateTime: msg.CreateTime,
        Content: msg.Content,
    }
    j,e := json.Marshal(t)
    if e != nil {
        logger.Logf("tDeliveryWorker.deliver, failed json.Marshal, id=%v, msg=%s/%s", me.info.ClientID, msg.GlobalID, msg.SubID)
        return false
    }

    r, e := http.Post(me.info.NotifyURL, "application/json", bytes.NewReader(j))
    if e != nil {
        logger.Logf("tDeliveryWorker.deliver, failed http.Post, id=%v, msg=%s/%s", me.info.ClientID, msg.GlobalID, msg.SubID)
        return false
    }

    defer r.Body.Close()
    rep, e := ioutil.ReadAll(r.Body)
    if e != nil {
        logger.Logf("tDeliveryWorker.deliver, failed ioutil.ReadAll, id=%v, msg=%s/%s", me.info.ClientID, msg.GlobalID, msg.SubID)
        return false
    }

    m := &models.OkMsg{}
    e = json.Unmarshal(rep, m)
    if e != nil {
        logger.Logf("tDeliveryWorker.deliver, failed json.Unmarshal, id=%v, msg=%s/%s", me.info.ClientID, msg.GlobalID, msg.SubID)
        return false
    }

    if m.OK {
        return true
    } else {
        logger.Logf("tDeliveryWorker.deliver, failed OkMsg.OK, id=%v, msg=%s/%s", me.info.ClientID, msg.GlobalID, msg.SubID)
        return false
    }
}

// handleDeliveringMsg: if delivery timeout, then retry delivery
func (me *tDeliveryWorker) handleDeliveringMsg(msg *models.QueuedMsg) {
    now := time.Now().UnixNano()
    if msg.UpdateTime + gDeliveryTimeoutNanos > now {
        return
    }

    // delivery timeout
    me.afterDeliveryTimeout(msg)
}

// afterDeliverySuccess: if done, move msg to success queue
func (me *tDeliveryWorker) afterDeliverySuccess(msg *models.QueuedMsg) {
    err := database.TX(func(db *sqlx.DB, tx *sqlx.Tx) error {
        r,e := db.Exec(
    "delete from delivery_queue where id=? and update_time=? and status_flag=1",
            msg.ID,
            msg.UpdateTime,
        )
        if e != nil {
            return e
        }

        rows, e := r.RowsAffected()
        if e != nil {
            return e
        }
        if rows != 1 {
            return gOneRowsErr
        }

        r, e = db.Exec(
            "insert into success_queue (msg_id, client_id, create_time) values(?, ?, ?)",
            msg.ID,
            msg.ClientID,
            time.Now().UnixNano(),
        )
        if e != nil {
            return e
        }

        rows, e = r.RowsAffected()
        if e != nil {
            return e
        }
        if rows != 1 {
            return gOneRowsErr
        }

        return nil
    })

    if err != nil {
        logger.Logf("tDeliveryWorker.afterDeliverySuccess, failed, id=%v, msg=%s/%s, err=%s", me.info.ClientID, msg.GlobalID, msg.SubID, err.Error())
    } else {
        logger.Logf("tDeliveryWorker.afterDeliverySuccess, done, id=%v, msg=%s/%s", me.info.ClientID, msg.GlobalID, msg.SubID)
    }
}


// afterDeliveryFailed: if failed, do nothing but just log it
func (me *tDeliveryWorker) afterDeliveryFailed(msg *models.QueuedMsg) {
    logger.Logf("tDeliveryWorker.afterDeliveryFailed, id=%v, msg=%s/%s", me.info.ClientID, msg.GlobalID, msg.SubID)
}

// afterDeliveryTimeout: if timeout, then reset status and retry
func (me *tDeliveryWorker) afterDeliveryTimeout(msg *models.QueuedMsg) {
    err := database.DB(func(db *sqlx.DB) error {
        r,e := db.Exec(
            "update delivery_queue set status_flag=0 where id=? and status_flag=1 and update_time=?",
            msg.ID,
            msg.UpdateTime,
        )
        if e != nil {
            return e
        }

        rows,e := r.RowsAffected()
        if e != nil {
            return e
        }

        if rows != 1 {
            return gOneRowsErr
        }

        return nil
    })

    if err != nil {
        logger.Logf("tDeliveryWorker.afterDeliveryTimeout, failed, id=%v, msg=%s/%s, err=%s", me.info.ClientID, msg.GlobalID, msg.SubID, err.Error())
    } else {
        logger.Logf("tDeliveryWorker.afterDeliveryTimeout, done, id=%v, msg=%s/%s", me.info.ClientID, msg.GlobalID, msg.SubID)
    }
}

var gEmptyRowsErr = errors.New("empty rows")
var gOneRowsErr = errors.New("expecting one row affected")
var gDeliveryTimeoutNanos = int64(10 * (time.Second / time.Nanosecond))

database.go

数据库表相应的细节调整
- delivery_queue: 去掉failed_count, 增加update_time时间戳
- success_queue: 去掉sub_id, 改为client_id, 并增加create_time时间戳
- failed_queue: 因为不允许失败, 因此删除失败投递表

package database

import "github.com/jmoiron/sqlx"
import _ "github.com/mattn/go-sqlite3"

type DBFunc func(db *sqlx.DB) error
type TXFunc func(db *sqlx.DB, tx *sqlx.Tx) error

func init() {
    // must prepare tables
    err := DB(initDB)
    if err != nil {
        panic(err)
    }
}

func initDB(db *sqlx.DB) error {
    // 订阅者/消费者: subscriber
    _, e := db.Exec(`create table if not exists subscriber(
    id integer primary key autoincrement,
    client_id varchar(50) unique not null,
    topic varchar(100) not null,
    notify_url varchar(500) not null,
    expire_time integer
)`)
    if e != nil {
        return e
    }

    // 事务消息: tx_msg
    _, e = db.Exec(`create table if not exists tx_msg (
    id integer primary key autoincrement,
    global_id string varchar(50) not null,
    sub_id string varchar(50) unique not null,
    sender_id varchar(50) not null,
    create_time integer not null,
    topic varchar(100) not null,
    content nvarchar(2048) not null
)`)
    if e != nil {
        return e
    }

    // 投递队列: delivery_queue
    _, e = db.Exec(`create table if not exists delivery_queue (
    id integer primary key autoincrement,
    
    client_id varchar(50) not null,
    notify_url varchar(500) not null,
    
    msg_id integer not null,
    global_id string varchar(50) not null,
    sub_id string varchar(50) unique not null,
    sender_id varchar(50) not null,
    create_time integer not null,
    topic varchar(100) not null,
    content nvarchar(2048) not null,
    
    status_flag integer not null,
    update_time integer not null
)`)
    if e != nil {
        return e
    }

    // 成功投递队列: success_queue
    _, e = db.Exec(`create table if not exists success_queue (
    id integer primary key autoincrement,
    msg_id integer not null,
    client_id varchar(50) not null,
    create_time integer not null
)`)
    if e != nil {
        return e
    }

//  // 投递失败队列: failed_queue
//  _, e = db.Exec(`create table if not exists failed_queue (
//  id integer primary key autoincrement,
//  msg_id integer not null,
//  client_id varchar(50) not null,
//    create_time integer not null
//)`)
//  if e != nil {
//      return e
//  }

    return nil
}

func open() (*sqlx.DB, error) {
    return sqlx.Open("sqlite3", "./mqs.db")
}

func DB(action DBFunc) error {
    db,err := open()
    if err != nil {
        return err
    }
    defer func() { _ = db.Close() }()

    return action(db)
}

func TX(action TXFunc) error {
    return DB(func(db *sqlx.DB) error {
        tx, err := db.Beginx()
        if err != nil {
            return err
        }

        err = action(db, tx)
        if err == nil {
            return tx.Commit()
        } else {
            return tx.Rollback()
        }
    })
}

(未完待续)

手撸golang GO与微服务 Saga模式之4

缘起

Saga模式

目标

子目标(Day 4)

tDeliveryWorker.go

database.go

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