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WITH (UPDLOCK,HOLDLOCK)提示與不同表類型
我們先來了解下UPDLOCK和HOLDLOCK的概念。
UPDLOCK
指定采用更新鎖并保持到事務(wù)完成。 UPDLOCK 僅對(duì)行級(jí)別或頁級(jí)別的讀操作采用更新鎖。 如果將 UPDLOCK 與 TABLOCK 組合使用或出于一些其他原因采用表級(jí)鎖,將采用排他 (X) 鎖。
HOLDLOCK
等價(jià)于SERIALIZABLE。保持共享鎖直到事務(wù)完成,使共享鎖更具有限制性;而不是無論事務(wù)是否完成,都在不再需要所需表或數(shù)據(jù)頁時(shí)立即釋放共享鎖。并且至少整個(gè)查詢覆蓋的范圍會(huì)被鎖定,以阻止導(dǎo)致幻象讀的插入。
一個(gè)U鎖是與其他的S鎖兼容的,但是與其他的U鎖不兼容。(查看鎖兼容性)。因此,如果鎖在行級(jí)別或者頁級(jí)別采用,這將不會(huì)阻塞其他讀操作,除非他們也使用UPDLOCK提示。
首先,創(chuàng)建一個(gè)堆表,插入一些測(cè)試數(shù)據(jù):
CREATE FUNCTION dbo.RANDBETWEEN(@minval TINYINT, @maxval TINYINT, @random NUMERIC(18,10)) RETURNS TINYINT AS BEGIN RETURN (SELECT CAST(((@maxval + 1) - @minval) * @random + @minval AS TINYINT)) END GO -- Create Person Table CREATE TABLE Person(ID int NOT NULL IDENTITY,FirstName varchar(32) NULL,LastName varchar(32) NULL,CityId int NULL); GO -- Insert 1 million records into the Person table INSERT INTO Person (FirstName,LastName,CityId) SELECT TOP 1000000 CASE WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 0 THEN 'John' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 1 THEN 'Jack' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 2 THEN 'Bill' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 3 THEN 'Mary' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 4 THEN 'Kate' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 5 THEN 'Matt' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 6 THEN 'Rachel' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 7 THEN 'Tom' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 8 THEN 'Ann' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 9 THEN 'Andrew' ELSE 'Bob' END AS FirstName, CASE WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 0 THEN 'Smith' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 1 THEN 'Morgan' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 2 THEN 'Simpson' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 3 THEN 'Walker' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 4 THEN 'Bauer' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 5 THEN 'Taylor' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 6 THEN 'Morris' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 7 THEN 'Elliot' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 8 THEN 'White' WHEN dbo.RANDBETWEEN(0,9,RAND(CHECKSUM(NEWID()))) = 9 THEN 'Davis' ELSE 'Brown' END AS LastName, dbo.RANDBETWEEN(1,15,RAND(CHECKSUM(NEWID()))) as CityId FROM sys.all_objects a CROSS JOIN sys.all_objects b GO SELECT * FROM Person;
堆表
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (UPDLOCK, HOLDLOCK) WHERE ID = 1; SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
非聚集索引表
在堆表的ID列創(chuàng)建非聚集索引:
CREATE NONCLUSTERED INDEX IX_Person_ID ON dbo.Person (ID);
場(chǎng)景1:
使用WITH (HOLDLOCK)而沒有WHERE從句,來觀察鎖升級(jí)。
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (HOLDLOCK); SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
場(chǎng)景2:
使用WITH(HOLDLOCK)和WHERE從句,從ID列索引查找。
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (HOLDLOCK) WHERE ID = 1; SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
場(chǎng)景3:
使用WITH (UPDLOCK, HOLDLOCK)和WHERE從句,從ID列索引查找。
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (INDEX (0), UPDLOCK, HOLDLOCK) WHERE ID = 1; SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] --,p.* FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
場(chǎng)景4:
使用WITH (INDEX (0), UPDLOCK, HOLDLOCK),強(qiáng)制表掃描。
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (INDEX (0), UPDLOCK, HOLDLOCK) WHERE ID = 1; SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] --,p.* FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
聚集索引表
刪除掉非聚集索引,并創(chuàng)建ID列的聚集索引:
DROP INDEX Person.IX_Person_ID GO ALTER TABLE dbo.Person ADD CONSTRAINT PK_Person PRIMARY KEY CLUSTERED (ID) GO
場(chǎng)景1:
使用WIH (HOLDLOCK)而無WHERE條件。
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (HOLDLOCK); SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] --,p.* FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
場(chǎng)景2:
使用WITH (UPDLOCK, HOLDLOCK)而無WHERE條件。
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (UPDLOCK, HOLDLOCK); SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] --,p.* FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
場(chǎng)景3:
使用WITH (UPDLOCK, HOLDLOCK)和WHERE條件,走ID列聚集索引查找。
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (UPDLOCK, HOLDLOCK) WHERE ID = 1; SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] --,p.* FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
接著,在CityId列建立非聚集索引:
CREATE INDEX IX_Person_CityId ON Person(CityId);
查看CityId的數(shù)據(jù)分布情況:
SELECT CityId,COUNT(*) AS CNT FROM dbo.Person GROUP BY CityId ORDER BY 2 DESC
場(chǎng)景4:
查詢CityId為1
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (UPDLOCK, HOLDLOCK) WHERE CityId=1; SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] --,p.* FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
插入一個(gè)可選擇性更強(qiáng)的CityId值:
INSERT Person(FirstName,LastName,CityId) SELECT 'ryan','xu',99 UNION ALL SELECT 'koko','xu',99 UNION ALL SELECT 'jerry','xu',100 GO
場(chǎng)景5:
查詢CityId為99
BEGIN TRANSACTION SELECT * FROM dbo.Person WITH (UPDLOCK, HOLDLOCK) WHERE CityId=99; SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] --,p.* FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
接著,刪除CityId列索引,創(chuàng)建該列包含索引。
DROP INDEX Person.IX_Person_CityId; GO CREATE INDEX IX_Person_CityId ON Person(CityId) INCLUDE(FirstName); GO
場(chǎng)景6:
同樣查詢CityID為99,單輸出列在包含索引中,完全走非聚集索引的查找。(主鍵列默認(rèn)包含在非聚集索引中)
BEGIN TRANSACTION SELECT ID,FirstName FROM dbo.Person WITH (UPDLOCK, HOLDLOCK) WHERE CityId=99; SELECT [request_session_id], c.[program_name], DB_NAME(c.[dbid]) AS dbname, [resource_type], [request_status], [request_mode], [resource_description], OBJECT_NAME(p.[object_id]) AS objectname, p.[index_id] --,p.* FROM sys.[dm_tran_locks] AS a LEFT JOIN sys.[partitions] AS p ON a.[resource_associated_entity_id]=p.[hobt_id] LEFT JOIN sys.[sysprocesses] AS c ON a.[request_session_id]=c.[spid] WHERE c.[dbid]=DB_ID(DB_NAME()) AND a.[request_session_id]=@@SPID ORDER BY [request_session_id],[resource_type]; COMMIT TRANSACTION
總結(jié)
對(duì)于查詢:
SELECT * FROM tblTest WITH (UPDLOCK, HOLDLOCK)
如果查詢計(jì)劃顯示了一個(gè)堆表上的掃描,那么你總是獲得一個(gè)對(duì)象上的X鎖。如果是一個(gè)索引掃描,它依賴于使用的鎖粒度。(單個(gè) Transact-SQL 語句在單個(gè)無分區(qū)表或索引上獲得至少 5,000 個(gè)鎖,將觸發(fā)鎖升級(jí))
對(duì)于非聚集索引表,HOLDLOCK在(ffffffffffff)上采用了RangeS-S鎖,UPDLOCK, HOLDLOCK采用了 RangeS-U鎖。兩個(gè)查詢都通過ID列執(zhí)行了索引查找。當(dāng)我使用WITH (INDEX (0), UPDLOCK, HOLDLOCK)強(qiáng)制執(zhí)行計(jì)劃執(zhí)行表掃描時(shí),看到對(duì)象上采用X鎖。如果索引可以用于在執(zhí)行計(jì)劃中識(shí)別范圍查詢,將使用鍵范圍鎖。
對(duì)于聚集索引表,當(dāng)WHERE條件走聚集索引查找,UPDLOCK, HOLDLOCK采用了KEY上的U鎖。只有純粹只走非聚集索引查找時(shí),才用了KEY上的Ranges-U鎖。
因?yàn)槟闶褂昧薍OLDLOCK,它阻止了幻象讀。如果你的查詢讀取了整個(gè)表,那么阻止了范圍的幻象讀,意思是它不允許任何行被插入。為了獲得一個(gè)鍵范圍鎖你的查詢需要合適的索引和WHERE從句。
參考
表提示
https://msdn.microsoft.com/zh-cn/library/ms187373.aspx
鎖升級(jí)
https://msdn.microsoft.com/zh-cn/library/ms184286(v=sql.105).aspx
How to resolve blocking problems that are caused by lock escalation in SQL Server
https://support.microsoft.com/en-us/kb/323630
鍵范圍鎖定
https://technet.microsoft.com/zh-cn/library/ms191272(en-us,SQL.110).aspx
SQL Server 的事務(wù)和鎖(二)-Range S-S鎖
http://www.cnblogs.com/lxconan/archive/2011/10/21/sql_transaction_n_locks_2.html
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