布景
众所周知,数据库的单行并发写才能极为有限,比如 MySQL 的单行并发写大概在300~500TPS之间。所以,将数据分桶存储能够线性提升并发写入才能。分桶处理的是单个数据库的并发才能。
分桶模型
每一个桶咱们能够当作单个数据库中的一行记载,将原来的一行记载存储100件库存,变为用5行记载别离存储20件库存。在对库存进行操作的时分,就能够通过对用户ID取模,确认该用户操纵的是那一行记载,然后进步单个数据库的并发才能。
在秒杀场景中,咱们要对库存的数量进行缓存,所以也要对缓存进行分桶。每一个桶当作Redis中的一个记载即可。
缓存中的数据相当于库存的预扣减,预扣减成功那么就让该请求去修改数据库,失利直接拒绝该请求即可。这里尽量坚持缓存数据(弱共同)与数据库中的数据(强共同)的共同性,但是缓存和数据库分桶之间的关系是一定要确保的。
分桶规划与完成
分桶编列思路
在整个分桶编列的过程,有几个重要的点:
- 在进行分桶编列之前,要先暂停分桶服务,设置为维护状况,此时用户无法下单;
- 暂停分桶服务时,有必要运用独立业务手动提交,确保在继续执行分桶前,分桶状况已经提交到数据库;
- 分桶保存到数据库后,应同步数据到缓存中;
- 全量和增量:全量分桶意味着将当时传入的库存总量作为最终总量,从头计算分桶数据;而增量分桶则是将传入的库存总量累加到已有的库存中,然后再从头计算分桶数据;
- 有无前史分桶数据:假如此前已有分桶数据,那么在分桶时则要先进行库存收回,随后再统一分配;假如此前无分桶数据,则直接创立新的分桶集;
- 分桶中出现任何反常应抛出以触发业务回滚;
- 不管分桶成功或失利,最终都要从头翻开分桶服务,即撤销分桶维护状况,不然秒杀品将无法售卖;
分桶编列代码完成
分桶编列代码:
public void arrangeStockBuckets(Long itemId, Integer totalStocksAmount, Integer bucketsQuantity, Integer arrangementMode) {
logger.info("arrangeBuckets|预备库存分桶|{},{},{}", itemId, totalStocksAmount, bucketsQuantity);
if (itemId == null || totalStocksAmount == null || totalStocksAmount < 0 || bucketsQuantity == null || bucketsQuantity <= 0) {
throw new StockBucketException(ErrorCode.INVALID_PARAMS);
}
// 确保只要一个线程对itemId进行更新
DistributedLock distributedLock = distributedLockFactoryService.getDistributedLock(ITEM_STOCK_BUCKETS_SUSPEND_KEY + itemId);
try {
boolean tryLock = distributedLock.tryLock(5, 5, TimeUnit.SECONDS);
if (!tryLock) {
logger.info("arrangeStockBuckets|获取锁失利|{}", itemId);
return;
}
// 手动添加业务
TransactionStatus transactionStatus = dataSourceTransactionManager.getTransaction(transactionDefinition);
try {
// 设置为禁用状况
logger.info("suspendBuckets|禁用库存分桶|{}", itemId);
int updateStatusByItemId = seckillBucketMapper.updateStatusByItemId(itemId, SeckillBucketStatus.DISABLED.getCode());
if (updateStatusByItemId < 0) {
logger.info("arrangeBuckets|关闭库存分桶失利|{}", itemId);
throw new StockBucketException(ErrorCode.ARRANGE_STOCK_BUCKETS_FAILED);
}
logger.info("suspendBuckets|库存分桶已禁用|{}", itemId);
dataSourceTransactionManager.commit(transactionStatus);
} catch (Exception e) {
logger.info("arrangeBuckets|关闭分桶失利回滚中|{}", itemId, e);
dataSourceTransactionManager.rollback(transactionStatus);
}
List<SeckillBucket> seckillBuckets = seckillBucketMapper.selectByItemId(itemId);
if (seckillBuckets == null || seckillBuckets.size() == 0) {
initStockBuckets(itemId, totalStocksAmount, bucketsQuantity);
return;
}
// 依据总量分桶
if (ArrangementMode.isTotalAmountMode(arrangementMode)) {
arrangeStockBucketsBasedTotalMode(itemId, totalStocksAmount, bucketsQuantity, seckillBuckets);
}
// 依据增量分桶
if (ArrangementMode.isIncrementalAmountMode(arrangementMode)) {
rearrangeStockBucketsBasedIncrementalMode(itemId, totalStocksAmount, bucketsQuantity, seckillBuckets);
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
构建(初始化)分桶代码:
private void initStockBuckets(Long itemId, Integer totalStocksAmount, Integer bucketsQuantity) {
SeckillBucket primaryBucket = new SeckillBucket()
.initPrimary()
.setItemId(itemId)
.setTotalStocksAmount(totalStocksAmount);
List<SeckillBucket> presentBuckets = buildBuckets(itemId, totalStocksAmount, bucketsQuantity, primaryBucket);
submitBucketsToArrange(itemId, presentBuckets);
}
private List<SeckillBucket> buildBuckets(Long itemId, Integer totalStocksAmount, Integer bucketsQuantity, SeckillBucket primaryBucket) {
if (itemId == null || totalStocksAmount == null || bucketsQuantity == null || bucketsQuantity <= 0) {
throw new StockBucketException(ErrorCode.INVALID_PARAMS);
}
List<SeckillBucket> seckillBucketList = new ArrayList<>();
Integer averageStockAmount = totalStocksAmount / bucketsQuantity;
Integer remainStockAmount = totalStocksAmount % bucketsQuantity;
for (int i = 0; i < bucketsQuantity; i++) {
if (i == 0) {
if (primaryBucket == null) {
primaryBucket = new SeckillBucket();
}
primaryBucket
.setAvailableStocksAmount(averageStockAmount)
.setSerialNo(i)
.setStatus(SeckillBucketStatus.ENABLED.getCode());
seckillBucketList.add(primaryBucket);
continue;
}
SeckillBucket seckillBucket = new SeckillBucket()
.setSerialNo(i)
.setStatus(SeckillBucketStatus.ENABLED.getCode())
.setItemId(itemId);
if (i < bucketsQuantity - 1) {
seckillBucket.setAvailableStocksAmount(averageStockAmount)
.setTotalStocksAmount(averageStockAmount);
}
if (i == bucketsQuantity - 1) {
Integer restAvailableStocksAmount = averageStockAmount + remainStockAmount;
seckillBucket.setAvailableStocksAmount(restAvailableStocksAmount)
.setTotalStocksAmount(restAvailableStocksAmount);
}
seckillBucketList.add(seckillBucket);
}
return seckillBucketList;
}
存储入缓存和数据库代码:
先入数据库再入缓存。
private void submitBucketsToArrange(Long itemId, List<SeckillBucket> presentBuckets) {
logger.info("arrangeBuckets|编列库存分桶|{},{}", itemId, JSON.toJSONString(presentBuckets));
if (itemId == null || itemId <= 0 || CollectionUtils.isEmpty(presentBuckets)) {
logger.info("arrangeBuckets|库存分桶参数过错|{}", itemId);
throw new BusinessException(ErrorCode.INVALID_PARAMS);
}
// 先删除再参加
seckillBucketMapper.deleteById(itemId);
int insertBatch = seckillBucketMapper.insertBatch(presentBuckets);
if (insertBatch > 1) {
// 存入缓存
presentBuckets.forEach((seckillBucket -> {
distributedCacheService.put(getBucketAvailableStocksCacheKey(itemId, seckillBucket.getSerialNo()), seckillBucket.getAvailableStocksAmount());
distributedCacheService.put(getItemStockBucketsQuantityCacheKey(itemId), presentBuckets.size());
}));
} else {
logger.info("submitBucketsToArrange|库存分桶过错|{}, {}", itemId, JSON.toJSONString(presentBuckets));
throw new StockBucketException(ErrorCode.ARRANGE_STOCK_BUCKETS_FAILED);
}
}
依据全量分桶
private void arrangeStockBucketsBasedTotalMode(Long itemId, Integer totalStocksAmount, Integer bucketsQuantity, List<SeckillBucket> existingBuckets) {
// 计算子桶的剩下的库存数
int remainAvailableStocks = existingBuckets.stream()
.filter(SeckillBucket::isSubSeckillBucket)
.mapToInt(SeckillBucket::getAvailableStocksAmount).sum();
Optional<SeckillBucket> optionalSeckillBucket = existingBuckets.stream().filter(SeckillBucket::isPrimarySeckillBucket).findFirst();
if (!optionalSeckillBucket.isPresent()) {
throw new StockBucketException(ErrorCode.PRIMARY_BUCKET_IS_MISSING);
}
// 收回分桶库存到主桶
SeckillBucket primarySeckillBucket = optionalSeckillBucket.get();
primarySeckillBucket.addAvailableStocks(remainAvailableStocks);
// 已售出的库存
int soldStocksAmount = primarySeckillBucket.getTotalStocksAmount() - primarySeckillBucket.getAvailableStocksAmount();
if (soldStocksAmount > totalStocksAmount) {
throw new StockBucketException(799, "已售库存大于当期所设库存总量!");
}
// 设置最新库存,从头分桶
primarySeckillBucket.setTotalStocksAmount(totalStocksAmount);
List<SeckillBucket> seckillBucketList = buildBuckets(itemId, totalStocksAmount, bucketsQuantity, primarySeckillBucket);
submitBucketsToArrange(itemId, seckillBucketList);
}
依据增量分桶
private void rearrangeStockBucketsBasedIncrementalMode(Long itemId, Integer incrementalStocksAmount, Integer bucketsQuantity, List<SeckillBucket> existingBuckets) {
Optional<SeckillBucket> optionalSeckillBucket = existingBuckets.stream().filter(SeckillBucket::isPrimarySeckillBucket).findFirst();
if (!optionalSeckillBucket.isPresent()) {
throw new StockBucketException(ErrorCode.PRIMARY_BUCKET_IS_MISSING);
}
// 收回分桶库存 (获取当时一切桶剩下的可用库存数)
int remainAvailableStocks = existingBuckets.stream().mapToInt(SeckillBucket::getAvailableStocksAmount).sum();
// 加上要添加的库存数
Integer totalAvailableStocks = remainAvailableStocks + incrementalStocksAmount;
int presentAvailableStocks = remainAvailableStocks + incrementalStocksAmount;
if (presentAvailableStocks < 0) {
throw new StockBucketException(ErrorCode.STOCK_NOT_ENOUGH);
}
SeckillBucket primarySeckillBucket = optionalSeckillBucket.get();
primarySeckillBucket.increaseTotalStocksAmount(incrementalStocksAmount);
List<SeckillBucket> seckillBucketList = buildBuckets(itemId, totalAvailableStocks, bucketsQuantity, primarySeckillBucket);
submitBucketsToArrange(itemId, seckillBucketList);
}
不同分桶之间的数量差异
存在问题
用户在访问可用库存的时分,会存在一个问题:路由到不同分桶的流量或许存在差异和不均,这会导致不同分桶的余量不同,展现到不同用户上的数量就会不同。例如:#1桶中库存为0,但#2桶中库存大于0。
处理方法
- 规划库存借用机制,当某个分桶库存缺乏时,能够从其他桶借库存;
- 主桶和分桶留有一定冗余库存,分桶库存缺乏时能够向主桶申请;
- 答应不同用户看到不同的库存余量,所路由到的分桶没有库存时直接展现无库存;
在秒杀场景中,咱们一般挑选第三种,因为它满足的简略高效,重点维护服务端的数据共同性与极致的功能。前面两种方法会大大添加体系的复杂度,在挑选的时分要慎重考虑。
扣减库存完成代码
先扣除缓存在扣减数据库,缓存充当一个预扣减的作用,这里不再详细讨论。参考文章:/post/718520…
扣减缓存库存的Lua脚本
--- 对应的库存键不存在
if (redis.call('exists', KEYS[1]) == 0) then
return -996
end
--- 分桶禁用锁
if (redis.call('exists', KEYS[2]) == 1) then
return -998
end
--- 库存调度锁
if (redis.call('exists', KEYS[3]) == 1) then
return -997
end
if (redis.call('exists', KEYS[1]) == 1) then
local stocksAmount = tonumber(redis.call('get', KEYS[1]))
local quantity = tonumber(ARGV[1])
--- 库存不行
if (stocksAmount < quantity) then
return -1
end
if (stocksAmount >= quantity) then
redis.call('incrby', KEYS[1], 0 - quantity)
return 1
end
end
return -10000
运用达观锁扣减数据库库存
<update id="decreaseBucketStock">
update seckill_bucket
set available_stocks_amount = available_stocks_amount - #{quantity,jdbcType=NUMERIC}
where item_id = #{itemId,jdbcType=NUMERIC}
AND serial_no = #{serialNo,jdbcType=NUMERIC}
AND available_stocks_amount = #{oldAvailableStocksAmount,jdbcType=NUMERIC}
AND available_stocks_amount <![CDATA[ >= ]]> #{quantity,jdbcType=NUMERIC}
</update>