團隊更換新框架。新的業務全部使用新的框架，甚至是新的數據庫--Mysql。
這邊之前一直是使用oracle，各種訂單號、流水號、批次號啥的，都是直接使用oracle的sequence提供的數字序列號。現在數據庫更換成Mysql了，顯然以前的老方法不能適用了。
需要新寫一個：
- 分布式場景使用
- 滿足一定的並發要求
找了一些相關的資料，發現mysql這方面的實現，原理都是一條數據庫記錄，不斷update它的值。然后大部分的實現方案，都用到了函數。
貼一下網上的代碼：
基於mysql函數實現
表結構
CREATE TABLE `t_sequence` (
`sequence_name` varchar(64) CHARACTER SET utf8 COLLATE utf8_general_ci NOT NULL COMMENT '序列名稱' ,
`value` int(11) NULL DEFAULT NULL COMMENT '當前值' ,
PRIMARY KEY (`sequence_name`)
)
ENGINE=InnoDB
DEFAULT CHARACTER SET=utf8 COLLATE=utf8_general_ci
ROW_FORMAT=COMPACT
;
獲取下一個值
CREATE DEFINER = `root`@`localhost` FUNCTION `nextval`(sequence_name varchar(64))
RETURNS int(11)
BEGIN
declare current integer;
set current = 0;
update t_sequence t set t.value = t.value + 1 where t.sequence_name = sequence_name;
select t.value into current from t_sequence t where t.sequence_name = sequence_name;
return current;
end;
並發場景有可能會出問題，雖然可以在業務層加鎖，但分布式場景就無法保證了，然后效率應該也不會高。
自己實現一個，java版
原理：
- 讀取一條記錄，緩存一個數據段，如：0-100，將記錄的當前值從0修改為100
- 數據庫樂觀鎖更新，允許重試
- 讀取數據從緩存中讀取，用完再讀取數據庫
不廢話，上代碼：
基於java實現
表結構
每次update，都是將SEQ_VALUE設置為SEQ_VALUE+STEP
CREATE TABLE `t_pub_sequence` (
`SEQ_NAME` varchar(128) CHARACTER SET utf8 NOT NULL COMMENT '序列名稱',
`SEQ_VALUE` bigint(20) NOT NULL COMMENT '目前序列值',
`MIN_VALUE` bigint(20) NOT NULL COMMENT '最小值',
`MAX_VALUE` bigint(20) NOT NULL COMMENT '最大值',
`STEP` bigint(20) NOT NULL COMMENT '每次取值的數量',
`TM_CREATE` datetime NOT NULL COMMENT '創建時間',
`TM_SMP` datetime NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改時間',
PRIMARY KEY (`SEQ_NAME`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COMMENT='流水號生成表';
sequence接口
/**
* <p></p>
* @author coderzl
* @Title MysqlSequence
* @Description 基於mysql數據庫實現的序列
* @date 2017/6/6 23:03
*/
public interface MysqlSequence {
/**
* <p>
* 獲取指定sequence的序列號
* </p>
* @param seqName sequence名
* @return String 序列號
*/
public String nextVal(String seqName);
}
序列區間
用於本地緩存一段序列，從min到max區間
/**
* <p></p>
*
* @author coderzl
* @Title SequenceRange
* @Description 序列區間，用於緩存序列
* @date 2017/6/6 22:58
*/
@Data
public class SequenceRange {
private final long min;
private final long max;
/** */
private final AtomicLong value;
/** 是否超限 */
private volatile boolean over = false;
/**
* 構造.
*
* @param min
* @param max
*/
public SequenceRange(long min, long max) {
this.min = min;
this.max = max;
this.value = new AtomicLong(min);
}
/**
* <p>Gets and increment</p>
*
* @return
*/
public long getAndIncrement() {
long currentValue = value.getAndIncrement();
if (currentValue > max) {
over = true;
return -1;
}
return currentValue;
}
}
BO
對應數據庫記錄
@Data
public class MysqlSequenceBo {
/**
* seq名
*/
private String seqName;
/**
* 當前值
*/
private Long seqValue;
/**
* 最小值
*/
private Long minValue;
/**
* 最大值
*/
private Long maxValue;
/**
* 每次取值的數量
*/
private Long step;
/** */
private Date tmCreate;
/** */
private Date tmSmp;
public boolean validate(){
//一些簡單的校驗。如當前值必須在最大最小值之間。step值不能大於max與min的差
if (StringUtil.isBlank(seqName) || minValue < 0 || maxValue <= 0 || step <= 0 || minValue >= maxValue || maxValue - minValue <= step ||seqValue < minValue || seqValue > maxValue ) {
return false;
}
return true;
}
}
DAO
增刪改查，其實就用到了改和查
public interface MysqlSequenceDAO {
/**
*
*/
public int createSequence(MysqlSequenceBo bo);
public int updSequence(@Param("seqName") String seqName, @Param("oldValue") long oldValue ,@Param("newValue") long newValue);
public int delSequence(@Param("seqName") String seqName);
public MysqlSequenceBo getSequence(@Param("seqName") String seqName);
public List<MysqlSequenceBo> getAll();
}
Mapper
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="com.xxxxx.core.sequence.impl.dao.MysqlSequenceDAO" >
<resultMap id="BaseResultMap" type="com.xxxxx.core.sequence.impl.MysqlSequenceBo" >
<result column="SEQ_NAME" property="seqName" jdbcType="VARCHAR" />
<result column="SEQ_VALUE" property="seqValue" jdbcType="BIGINT" />
<result column="MIN_VALUE" property="minValue" jdbcType="BIGINT" />
<result column="MAX_VALUE" property="maxValue" jdbcType="BIGINT" />
<result column="STEP" property="step" jdbcType="BIGINT" />
<result column="TM_CREATE" property="tmCreate" jdbcType="TIMESTAMP" />
<result column="TM_SMP" property="tmSmp" jdbcType="TIMESTAMP" />
</resultMap>
<delete id="delSequence" parameterType="java.lang.String" >
delete from t_pub_sequence
where SEQ_NAME = #{seqName,jdbcType=VARCHAR}
</delete>
<insert id="createSequence" parameterType="com.xxxxx.core.sequence.impl.MysqlSequenceBo" >
insert into t_pub_sequence (SEQ_NAME,SEQ_VALUE,MIN_VALUE,MAX_VALUE,STEP,TM_CREATE)
values (#{seqName,jdbcType=VARCHAR}, #{seqValue,jdbcType=BIGINT},
#{minValue,jdbcType=BIGINT}, #{maxValue,jdbcType=BIGINT}, #{step,jdbcType=BIGINT},
now())
</insert>
<update id="updSequence" parameterType="com.xxxxx.core.sequence.impl.MysqlSequenceBo" >
update t_pub_sequence
set SEQ_VALUE = #{newValue,jdbcType=BIGINT}
where SEQ_NAME = #{seqName,jdbcType=VARCHAR} and SEQ_VALUE = #{oldValue,jdbcType=BIGINT}
</update>
<select id="getAll" resultMap="BaseResultMap" >
select SEQ_NAME, SEQ_VALUE, MIN_VALUE, MAX_VALUE, STEP
from t_pub_sequence
</select>
<select id="getSequence" resultMap="BaseResultMap" >
select SEQ_NAME, SEQ_VALUE, MIN_VALUE, MAX_VALUE, STEP
from t_pub_sequence
where SEQ_NAME = #{seqName,jdbcType=VARCHAR}
</select>
</mapper>
接口實現
@Repository("mysqlSequence")
public class MysqlSequenceImpl implements MysqlSequence{
@Autowired
private MysqlSequenceFactory mysqlSequenceFactory;
/**
* <p>
* 獲取指定sequence的序列號
* </p>
*
* @param seqName sequence名
* @return String 序列號
* @author coderzl
*/
@Override
public String nextVal(String seqName) {
return Objects.toString(mysqlSequenceFactory.getNextVal(seqName));
}
}
工廠
工廠只做了兩件事
- 服務啟動的時候，初始化數據庫中所有sequence【完成序列區間緩存】
- 獲取sequence的下一個值
@Component
public class MysqlSequenceFactory {
private final Lock lock = new ReentrantLock();
/** */
private Map<String,MysqlSequenceHolder> holderMap = new ConcurrentHashMap<>();
@Autowired
private MysqlSequenceDAO msqlSequenceDAO;
/** 單個sequence初始化樂觀鎖更新失敗重試次數 */
@Value("${seq.init.retry:5}")
private int initRetryNum;
/** 單個sequence更新序列區間樂觀鎖更新失敗重試次數 */
@Value("${seq.get.retry:20}")
private int getRetryNum;
@PostConstruct
private void init(){
//初始化所有sequence
initAll();
}
/**
* <p> 加載表中所有sequence，完成初始化 </p>
* @return void
* @author coderzl
*/
private void initAll(){
try {
lock.lock();
List<MysqlSequenceBo> boList = msqlSequenceDAO.getAll();
if (boList == null) {
throw new IllegalArgumentException("The sequenceRecord is null!");
}
for (MysqlSequenceBo bo : boList) {
MysqlSequenceHolder holder = new MysqlSequenceHolder(msqlSequenceDAO, bo,initRetryNum,getRetryNum);
holder.init();
holderMap.put(bo.getSeqName(), holder);
}
}finally {
lock.unlock();
}
}
/**
* <p> </p>
* @param seqName
* @return long
* @author coderzl
*/
public long getNextVal(String seqName){
MysqlSequenceHolder holder = holderMap.get(seqName);
if (holder == null) {
try {
lock.lock();
holder = holderMap.get(seqName);
if (holder != null){
return holder.getNextVal();
}
MysqlSequenceBo bo = msqlSequenceDAO.getSequence(seqName);
holder = new MysqlSequenceHolder(msqlSequenceDAO, bo,initRetryNum,getRetryNum);
holder.init();
holderMap.put(seqName, holder);
}finally {
lock.unlock();
}
}
return holder.getNextVal();
}
}
單一sequence的Holder
- init() 初始化 其中包括參數校驗，數據庫記錄更新，創建序列區間
- getNextVal() 獲取下一個值
public class MysqlSequenceHolder {
private final Lock lock = new ReentrantLock();
/** seqName */
private String seqName;
/** sequenceDao */
private MysqlSequenceDAO sequenceDAO;
private MysqlSequenceBo sequenceBo;
/** */
private SequenceRange sequenceRange;
/** 是否初始化 */
private volatile boolean isInitialize = false;
/** sequence初始化重試次數 */
private int initRetryNum;
/** sequence獲取重試次數 */
private int getRetryNum;
/**
* <p> 構造方法 </p>
* @Title MysqlSequenceHolder
* @param sequenceDAO
* @param sequenceBo
* @param initRetryNum 初始化時，數據庫更新失敗后重試次數
* @param getRetryNum 獲取nextVal時，數據庫更新失敗后重試次數
* @return
* @author coderzl
*/
public MysqlSequenceHolder(MysqlSequenceDAO sequenceDAO, MysqlSequenceBo sequenceBo,int initRetryNum,int getRetryNum) {
this.sequenceDAO = sequenceDAO;
this.sequenceBo = sequenceBo;
this.initRetryNum = initRetryNum;
this.getRetryNum = getRetryNum;
if(sequenceBo != null)
this.seqName = sequenceBo.getSeqName();
}
/**
* <p> 初始化 </p>
* @Title init
* @param
* @return void
* @author coderzl
*/
public void init(){
if (isInitialize == true) {
throw new SequenceException("[" + seqName + "] the MysqlSequenceHolder has inited");
}
if (sequenceDAO == null) {
throw new SequenceException("[" + seqName + "] the sequenceDao is null");
}
if (seqName == null || seqName.trim().length() == 0) {
throw new SequenceException("[" + seqName + "] the sequenceName is null");
}
if (sequenceBo == null) {
throw new SequenceException("[" + seqName + "] the sequenceBo is null");
}
if (!sequenceBo.validate()){
throw new SequenceException("[" + seqName + "] the sequenceBo validate fail. BO:"+sequenceBo);
}
// 初始化該sequence
try {
initSequenceRecord(sequenceBo);
} catch (SequenceException e) {
throw e;
}
isInitialize = true;
}
/**
* <p> 獲取下一個序列號 </p>
* @Title getNextVal
* @param
* @return long
* @author coderzl
*/
public long getNextVal(){
if(isInitialize == false){
throw new SequenceException("[" + seqName + "] the MysqlSequenceHolder not inited");
}
if(sequenceRange == null){
throw new SequenceException("[" + seqName + "] the sequenceRange is null");
}
long curValue = sequenceRange.getAndIncrement();
if(curValue == -1){
try{
lock.lock();
curValue = sequenceRange.getAndIncrement();
if(curValue != -1){
return curValue;
}
sequenceRange = retryRange();
curValue = sequenceRange.getAndIncrement();
}finally {
lock.unlock();
}
}
return curValue;
}
/**
* <p> 初始化當前這條記錄 </p>
* @Title initSequenceRecord
* @Description
* @param sequenceBo
* @return void
* @author coderzl
*/
private void initSequenceRecord(MysqlSequenceBo sequenceBo){
//在限定次數內，樂觀鎖更新數據庫記錄
for(int i = 1; i < initRetryNum; i++){
//查詢bo
MysqlSequenceBo curBo = sequenceDAO.getSequence(sequenceBo.getSeqName());
if(curBo == null){
throw new SequenceException("[" + seqName + "] the current sequenceBo is null");
}
if (!curBo.validate()){
throw new SequenceException("[" + seqName + "] the current sequenceBo validate fail");
}
//改變當前值
long newValue = curBo.getSeqValue()+curBo.getStep();
//檢查當前值
if(!checkCurrentValue(newValue,curBo)){
newValue = resetCurrentValue(curBo);
}
int result = sequenceDAO.updSequence(sequenceBo.getSeqName(),curBo.getSeqValue(),newValue);
if(result > 0){
sequenceRange = new SequenceRange(curBo.getSeqValue(),newValue - 1);
curBo.setSeqValue(newValue);
this.sequenceBo = curBo;
return;
}else{
continue;
}
}
//限定次數內，更新失敗，拋出異常
throw new SequenceException("[" + seqName + "] sequenceBo update error");
}
/**
* <p> 檢查新值是否合法 新的當前值是否在最大最小值之間</p>
* @param curValue
* @param curBo
* @return boolean
* @author coderzl
*/
private boolean checkCurrentValue(long curValue,MysqlSequenceBo curBo){
if(curValue > curBo.getMinValue() && curValue <= curBo.getMaxValue()){
return true;
}
return false;
}
/**
* <p> 重置sequence當前值 ：當前sequence達到最大值時，重新從最小值開始 </p>
* @Title resetCurrentValue
* @param curBo
* @return long
* @author coderzl
*/
private long resetCurrentValue(MysqlSequenceBo curBo){
return curBo.getMinValue();
}
/**
* <p> 緩存區間使用完畢時，重新讀取數據庫記錄，緩存新序列段 </p>
* @Title retryRange
* @param SequenceRange
* @author coderzl
*/
private SequenceRange retryRange(){
for(int i = 1; i < getRetryNum; i++){
//查詢bo
MysqlSequenceBo curBo = sequenceDAO.getSequence(sequenceBo.getSeqName());
if(curBo == null){
throw new SequenceException("[" + seqName + "] the current sequenceBo is null");
}
if (!curBo.validate()){
throw new SequenceException("[" + seqName + "] the current sequenceBo validate fail");
}
//改變當前值
long newValue = curBo.getSeqValue()+curBo.getStep();
//檢查當前值
if(!checkCurrentValue(newValue,curBo)){
newValue = resetCurrentValue(curBo);
}
int result = sequenceDAO.updSequence(sequenceBo.getSeqName(),curBo.getSeqValue(),newValue);
if(result > 0){
sequenceRange = new SequenceRange(curBo.getSeqValue(),newValue - 1);
curBo.setSeqValue(newValue);
this.sequenceBo = curBo;
return sequenceRange;
}else{
continue;
}
}
throw new SequenceException("[" + seqName + "] sequenceBo update error");
}
}
總結
- 當服務重啟或異常的時候，會丟失當前服務所緩存且未用完的序列
- 分布式場景，多個服務同時初始化，或者重新獲取sequence時，樂觀鎖會保證彼此不沖突。A服務獲取0-99，B服務會獲取100-199，以此類推
- 當該sequence獲取較為頻繁時，增大step值，能提升性能。但同時服務異常時，損失的序列也較多
- 修改數據庫里sequence的一些屬性值，比如step，max等，再下一次從數據庫獲取時，會啟用新的參數
- sequence只是提供了有限個序列號（最多max-min個），達到max后，會循環從頭開始。
- 由於sequence會循環，所以達到max后，再獲取，就不會唯一。建議使用sequence來做業務流水號時，拼接時間。如：20170612235101+序列號
業務id拼接方法
@Service
public class JrnGeneratorService {
private static final String SEQ_NAME = "T_SEQ_TEST";
/** sequence服務 */
@Autowired
private MySqlSequence mySqlSequence;
public String generateJrn() {
try {
String sequence = mySqlSequence.getNextValue(SEQ_NAME);
sequence = leftPadding(sequence,8);
Calendar calendar = Calendar.getInstance();
SimpleDateFormat sDateFormat = new SimpleDateFormat("yyyyMMddHHmmss");
String nowdate = sDateFormat.format(calendar.getTime());
nowdate.substring(4, nowdate.length());
String jrn = nowdate + sequence + RandomUtil.getFixedLengthRandom(6);//10位時間＋8位序列 + 6位隨機數＝24位流水號
return jrn;
} catch (Exception e) {
//TODO
}
}
private String leftPadding(String seq,int len){
String res ="";
String str ="";
if(seq.length()<len){
for(int i=0;i<len-seq.length();i++){
str +="0";
}
}
res =str+seq;
return res;
}
}