今天在查询数据库的时候,向开发要了一条查询语句,发现在语句表的后面有with(nolock),不知道这是干啥用的,之前没遇到过,所以就差了下: 大家在写查询时,为了性能,往往会在表后面加一个nolock...接下来再来继续深入的了解下这个玩意吧 为什么会在查询的表后面加nolock标识?...小结:NOLOCK 语句执行时不发出共享锁,允许脏读 ,等于 READ UNCOMMITTED事务隔离级别 。nolock确实在查询时能提高速度,但它并不是没有缺点的,起码它会引起脏读。...最后说下nolock和with(nolock)的几个小区别: 1:SQL05中的同义词,只支持with(nolock); 2:with(nolock)的写法非常容易再指定索引。...跨服务器查询语句时 不能用with (nolock) 只能用nolock 同一个服务器查询时 则with (nolock)和nolock都可以用 比如SQL code: select * from
[Account] a WITH ( NOLOCK ) LEFT JOIN BBCFinance.dbo.AccountAdjustReceipt b WITH ( NOLOCK ) ON...) ON a.DistributorSysNo=distributor.SysNo LEFT JOIN BBCAccount.dbo.Vendor vendor WITH(NOLOCK)...[Account] a WITH ( NOLOCK ) LEFT JOIN BBCFinance.dbo.AccountAdjustReceipt b WITH ( NOLOCK ) ON...) ON a.DistributorSysNo=distributor.SysNo LEFT JOIN BBCAccount.dbo.Vendor vendor WITH(NOLOCK)...[Account] a WITH ( NOLOCK ) LEFT JOIN BBCAccount.dbo.BusinessType BU WITH ( NOLOCK
select xt.fuserid ,xt.fname,u.fname as fusername ,e.FName as fempname from t_xuntong_user xt with (nolock...) inner join t_user u with (nolock) on xt.fuserid=u.fuserid...inner join t_Emp e with(nolock) on u.FEmpID=e.FItemID...inner join t_Emp e with(nolock) on u.FEmpID=e.FItemID...left join icclasstype i2 with (nolock) on i2.FID=t1.FClassTypeID where 1=1
FROM fn_String_To_Table(@LotName,',',1) SELECT LotPK,LotName INTO #WorkLotPK FROM MMLots WITH(NOLOCK...SourceLotPK只能在这里求 SELECT a.LotPK,a.SourceLotPK into #WorkSourcePK FROM MMLotOperations a WITH(NOLOCK...)类似[先根据外部序列号求解序列号,再照搬第一个判断变量的方式] SELECT LotPK,LotName INTO #WorkLotPKX FROM MMLots WITH(NOLOCK...,b.LotName AS SourceLotName,NULL FROM #WorkSourcePK2X a JOIN (SELECT LotPK,LotName FROM MMLots WITH(NOLOCK...本文的优化思想很简单,关键点是避免全表扫描 & 注重SQL语句写法 & 索引,另外,如果你查询的表有可能会在查询时段更新,而实际业务需求允许脏读,可加with(nolock)预防查询被更新事物阻塞。
二、with (nolock)的介绍和使用。 为了性能,往往会在表后面加一个nolock,或者是with(nolock),其目的就是查询是不锁定表,从而达到提高查询速度的目的。...nolock确实在查询时能提高速度,但它并不是没有缺点的,起码它会引起脏读。...最后说下nolock和with(nolock)的几个小区别: 1:SQL05中的同义词,只支持with(nolock); 2:with(nolock)的写法非常容易再指定索引。...跨服务器查询语句时 不能用with (nolock) 只能用nolock 同一个服务器查询时 则with (nolock)和nolock都可以用 比如 SQL code select * from...[IP].a.dbo.table1 with (nolock) 这样会提示用错误select * from a.dbo.table1 with (nolock) 这样就可以 三、数据表死锁 如果对某一个进行了事务操作
fputc fputwc _fputtc_nolock _fputc_nolock _fputwc_nolock _fputtchar _fputchar _fputwchar _fputts... _getc_nolock _getwc_nolock _gettch _getch _getwch _gettch_nolock _getch_nolock _getwch_nolock... _gettchar getchar getwchar _gettchar_nolock _getchar_nolock _getwchar_nolock _gettche _getche... _putc_nolock _putwc_nolock _puttch _putch _putwch _puttch_nolock _putch_nolock _putwch_nolock... _ungetc_nolock _ungetwc_nolock _ungettch _ungetch _ungetwch _ungettch_nolock _ungetch_nolock
threading.Lock() lock.acquire() lock.release() import threading withlock=0 nolock=0 count=10000...withlock for i in range(count): lock.acquire() withlock-=1 lock.release() def innolock(): global nolock...for i in range(count): nolock+=1 def denolock(): global nolock for i in range(count): nolock-=...start() t4.start() t1.join() t2.join() t3.join() t4.join() print("%s" % withlock) print("%s" % nolock
rw,sync,no_root_squash) 上图所示的配置,假如server端内网IP是10.255.5.26,挂载到Z:,命令有2种,但前者在写权限上不完全ok,后者则没问题 mount -o nolock...-o mtype=hard -o timeout=60 \\10.255.5.26\c\server Z: (如果指定了挂载名,就不要用这种了,写权限上不完全ok) mount -o nolock -...mtype=hard 172.21.96.4:/c/test x: mount -o nolock mtype=hard 82.157.20.227:/c/test y: 前面已经说了这种方式不完全ok...linux客户端(假如有2个nfs server,外网IP分别是 82.157.20.227、43.152.194.72) mount -t nfs -o vers=3,nolock,proto=tcp...,noresvport 82.157.20.227:/c/test /mnt mount -t nfs -o vers=3,nolock,proto=tcp,noresvport 43.152.194.72
[ProductName1] as a2 from [ProductData] t1 with (nolock) where (t1....[Remark] as a2 from [OrderProduct] t2 with (nolock) where (t2....[Remark] as a2 from [OrderProduct] t2 with (nolock) where (t2....[Remark] as a2 from [OrderProduct] t2 with (nolock) where (t2....[Remark] as a2 from [OrderProduct] t2 with (nolock) where (t2.
Direction = 'O' SELECT TOP 1 @InboundBusinessID_ItemCatalog = ID FROM dbo.EDI_CFG_Business WITH(NOLOCK...Direction = 'I' SELECT TOP 1 @InboundBusinessID_Inventory = ID FROM dbo.EDI_CFG_Business WITH(NOLOCK...Direction = 'I' SELECT TOP 1 @InboundBusinessID_ShipNotice = ID FROM dbo.EDI_CFG_Business WITH(NOLOCK...Direction = 'I' SELECT TOP 1 @OutboundBusinessID_FunctionAck = ID FROM dbo.EDI_CFG_Business WITH(NOLOCK...Name_Direction from ( select ID,Name+Direction as Name_Direction FROM dbo.EDI_CFG_Business WITH(NOLOCK
BBCAccount.dbo.Account account ON account.SysNo = change.AccountSysNo LEFT JOIN BBCAccount.dbo.Vendor V WITH ( NOLOCK...) ON V.SysNo = Account.VendorSysNo LEFT JOIN BBCAccount.dbo.Distributor D WITH ( NOLOCK ) ON D.SysNo...BBCAccount.dbo.Account account ON account.SysNo = change.AccountSysNo LEFT JOIN BBCAccount.dbo.Vendor V WITH ( NOLOCK...) ON V.SysNo = Account.VendorSysNo LEFT JOIN BBCAccount.dbo.Distributor D WITH ( NOLOCK ) ON D.SysNo
8、 一些SQL查询语句应加上nolock 在SQL语句中加nolock是提高SQL Server并发性能的重要手段,在oracle中并不需要这样做,因为oracle的结构更为合理,有undo表空间保存...SQL Server 的读、写是会相互阻塞的,为了提高并发性能,对于一些查询,可以加上nolock,这样读的时候可以允许写,但缺点是可能读到未提交的脏数据。使用 nolock有3条原则。...(1) 查询的结果用于“插、删、改”的不能加nolock ! (2) 查询的表属于频繁发生页分裂的,慎用nolock !...,而此时nolock的查询正在发生,比如在第100页已经读过的记录,可能会因为页分裂而分到第101页,这有可能使得nolock查询在读101页时重复读到该条数据,产生“重复读”。...上面提到的哥们,在加了nolock后一些操作出现报错,估计有可能因为nolock查询产生了重复读,2条相同的记录去插入别的表,当然会发生主键冲突。
{ Method meth = getMethodNoSuper_nolock(cls, sel); // 方法是通过二分查找的算法进行查找的 if (meth...DEBUG_TASK_THREADS mutex_locker_t lock(cacheUpdateLock); cache_fill_nolock(cls, sel, imp, receiver...); #else _collecting_in_critical(); return; #endif } 在这里我们看到了一个熟悉的函数:cache_fill_nolock!!!...cache_fill_nolock是谁呢?就是我前面在OC类的原理探究(二)——方法的缓存中提到的方法缓存的入口!!!...之前我们知道在cache_fill_nolock里面进行扩容、缓存函数等,但是并不知道在哪里会调用cache_fill_nolock函数,现在我们知道cache_fill_nolock函数的调用的地方了
.* FROM BBCAccount.dbo.Account (NOLOCK) At LEFT JOIN ( SELECT *...FROM BBCAccount.dbo.BusinessType (NOLOCK) BT WHERE BT.ParentCode...ABC.InDate FROM BBCFinance.dbo.AccountBalanceChange (NOLOCK...) ABC LEFT JOIN BBCFinance.dbo.AccountAdjustReceipt (NOLOCK)AAR
mount -t nfs -o nolock 172.22.44.2:/home/lzl/rootbox_hi3521u_pure/qvs/vs /tmpfs/vs_pub mount -t nfs...-o nolock 172.22.44.2:/home/lzl/rootbox_hi3531/qvs /tmpfs/vs_pub /home/lzl/rootbox_hi3521u_4g/qvs /...root_fs),6M(vs_fs),2M(web_fs) pcimod=host pciclksel=16 nfsroot=172.22.44.2:/home/lzl/rootbox_hi3531/,nolock
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