SQL Server中如何定位Row Lock鎖定哪一行數據

在SQL Server中有時候會使用提示（Hint）強制SQL使用行鎖（Row Lock），前兩天有個同事諮詢了一個問題，如何定位Row Lock具體鎖定了哪一行。其實這個問題只適合研究一下，實際意義並不大，由於找到、定位被鎖定的行的代價開銷較大，而意義卻不怎麼大，並且使用場景也不多。那麼下面咱們來探討、研究一下這個問題吧：

 

 

在會話窗口（會話ID=65）下執行下面SQL語句，模擬SQL Server使用行鎖鎖定某一行記錄： 

 

USE AdventureWorks2012;

GO

SELECT  @@SPID;

BEGIN TRAN;

UPDATE  [dbo].[DatabaseLog] WITH ( ROWLOCK )

SET     TSQL = N'dddd'

WHERE   DatabaseLogID = 1;

--ROLLBACK;

 

 

 

在另一個會話窗口使用下面SQL查詢，咱們能看到相關鎖的一些信息，以下所示，可是這些信息還不夠詳細，咱們還須要更詳細的信息：

 

SELECT Db_name(RSC_DBID)                AS 'DATABASE_NAME', 

       CASE RSC_TYPE 

         WHEN 1 THEN 'null' 

         WHEN 2 THEN 'DATABASE' 

         WHEN 3 THEN 'FILE' 

         WHEN 4 THEN 'INDEX' 

         WHEN 5 THEN 'TABLE' 

         WHEN 6 THEN 'PAGE' 

         WHEN 7 THEN 'KEY' 

         WHEN 8 THEN 'EXTEND' 

         WHEN 9 THEN 'RID ( ROW ID)' 

         WHEN 10 THEN 'APPLICATION' 

       END                              AS 'REQUEST_TYPE', 

       CASE REQ_OWNERTYPE 

         WHEN 1 THEN 'TRANSACTION' 

         WHEN 2 THEN 'CURSOR' 

         WHEN 3 THEN 'SESSION' 

         WHEN 4 THEN 'ExSESSION' 

       END                              AS 'REQUEST_OWNERTYPE', 

       Object_name(RSC_OBJID, RSC_DBID) AS 'OBJECT_NAME', 

       PROCESS.HOSTNAME, 

       PROCESS.NT_DOMAIN, 

       PROCESS.NT_USERNAME, 

       PROCESS.PROGRAM_NAME, 

       SQLTEXT.TEXT 

FROM   sys.syslockinfo LOCK 

       JOIN sys.sysprocesses PROCESS 

         ON LOCK.REQ_SPID = PROCESS.SPID 

       CROSS apply sys.DM_EXEC_SQL_TEXT(PROCESS.SQL_HANDLE) SQLTEXT 

WHERE  PROCESS.SPID = 65 

 

 

 

 

查詢sys.dm_tran_locks咱們能夠獲得更詳細的信息，例如，從resource_description中咱們能夠獲得file_id=1, 頁面編號爲273，這個頁面的第一條記錄（0）

 

 

SELECT  resource_type ,

        resource_database_id , --數據庫id

        resource_description , --資源描述

        resource_associated_entity_id , --資源關聯實體id

        request_mode , --請求模式

        request_type , --請求類型

        request_status ,

        request_session_id , --請求會話id

        request_owner_type

FROM    sys.dm_tran_locks

WHERE   request_session_id = 65;

 

 

 

 

準備下面腳本，爲了後續咱們定位到行鎖鎖定哪一行記錄。準備好後面腳本後，咱們就能夠開始測試了。注意，須要開啓跟蹤DBCC TRACEON(3604)。不然DBCC PAGE沒有任何輸出信息

 

 

IF EXISTS (SELECT * FROM sys.objects WHERE type='U' AND name='DBCC_PAGE_RESULT')

    DROP TABLE DBCC_PAGE_RESULT;

GO

CREATE TABLE DBCC_PAGE_RESULT

(

    [ParentObject]      NVARCHAR(200),

    [Object]          NVARCHAR(2000),

    [Field]          NVARCHAR(4000),

    [Value]          NVARCHAR(MAX)

)

GO

CREATE PROCEDURE PRC_DBCC_PAGE

(

 @dbid        INT,

 @filenum    INT,

 @pagenum     INT

)

AS

 DBCC PAGE(@dbid, @filenum,  @pagenum, 3) WITH TABLERESULTS;

GO

DBCC TRACEON(3604)

;WITH    t AS ( SELECT   Object ,

                        Field ,

                        Value ,

                        CASE WHEN CHARINDEX('Column', Object) > 0

                             THEN CHARINDEX('Column', Object)

                             ELSE CHARINDEX('Offset', Object)

                        END AS substring_len

               FROM     dbo.DBCC_PAGE_RESULT dp

               WHERE    Object LIKE 'Slot%Column%'

                        OR Field = 'KeyHashValue'

             ),

        tt

          AS ( SELECT   Object ,

                        Field ,

                        Value ,

                        CAST(SUBSTRING(Object, LEN('Slot') + 1,

                                       substring_len - LEN('Slot') - 1) AS INT) AS row

               FROM     t

             ),

        ttt

          AS ( SELECT   Object ,

                        Field ,

                        Value ,

                        row ,    --第幾行  

                        MAX(CASE WHEN Field = 'KeyHashValue' THEN Value

                                 ELSE ''

                            END) OVER ( PARTITION BY row ) AS KeyHashValue

               FROM     tt

             )

    SELECT  *

    FROM    ttt

    WHERE   ttt.row = 0

 

 

以下截圖所示，就能夠找到行鎖（Row Lock）鎖定了row=0這行記錄（注意，這裏的行記錄是從0開始的，而不是1），也就是DatabaseLogID=1的記錄。若是1:273:2， 那麼查詢條件中row=2  這個表示這個頁面的第幾行記錄。

                                                                                                                                                                                                                                                      

 

 

 

 

可是，有時候你鎖定了一行，查詢sys.dm_tran_locks時，你會發現resource_type爲RID類型的記錄有好幾條，以下所示：

 

USE AdventureWorks2012;

GO

SELECT  @@SPID;

BEGIN TRAN;

UPDATE  [dbo].[DatabaseLog] WITH ( ROWLOCK )

SET     TSQL = N'dddd'

WHERE   DatabaseLogID = 21;

--ROLLBACK;

 

 

 

 

其實真正是數據頁的只有resource_description=1:273:4 這行記錄， 也就是說這行記錄位於Page Number=273下的第5條記錄

 

 

 

其它一些頁面，例如 1，295；  1,279等都不是數據頁，以下截圖所示：m_type的值表示這個是數據頁、索引頁、IAM頁等等。具體參考

 

m_type

·         This is the page type. The values you’re likely to see are:

o   1 – data page. This holds data records in a heap or clustered index leaf-level.

o   2 – index page. This holds index records in the upper levels of a clustered index and all levels of non-clustered indexes.

o   3 – text mix page. A text page that holds small chunks of LOB values plus internal parts of text tree. These can be shared between LOB values in the same partition of an index or heap.

o   4 – text tree page. A text page that holds large chunks of LOB values from a single column value.

o   7 – sort page. A page that stores intermediate results during a sort operation.

o   8 – GAM page. Holds global allocation information about extents in a GAM interval (every data file is split into 4GB chunks – the number of extents that can be represented in a bitmap on a single database page). Basically whether an extent is allocated or not. GAM = Global Allocation Map. The first one is page 2 in each file. More on these in this post.

o   9 – SGAM page. Holds global allocation information about extents in a GAM interval. Basically whether an extent is available for allocating mixed-pages. SGAM = Shared GAM. the first one is page 3 in each file. More on these in this post.

o   10 – IAM page. Holds allocation information about which extents within a GAM interval are allocated to an allocation unit (portion of a table or index). IAM = Index Allocation Map. More on these in this post.

o   11 – PFS page. Holds allocation and free space information about pages within a PFS interval (every data file is also split into approx 64MB chunks – the number of pages that can be represented in a byte-map on a single database page. PFS = Page Free Space. The first one is page 1 in each file. More on these in this post.

o   13 – boot page. Holds information about the database. There’s only one of these in the database. It’s page 9 in file 1.

o   15 – file header page. Holds information about the file. There’s one per file and it’s page 0 in the file.

o   16 – diff map page. Holds information about which extents in a GAM interval have changed since the last full or differential backup. The first one is page 6 in each file.

o   17 – ML map page. Holds information about which extents in a GAM interval have changed while in bulk-logged mode since the last backup. This is what allows you to switch to bulk-logged mode for bulk-loads and index rebuilds without worrying about breaking a backup chain. The first one is page 7 in each file.

o   18 – a page that’s be deallocated by DBCC CHECKDB during a repair operation.

o   19 – the temporary page that ALTER INDEX … REORGANIZE (or DBCC INDEXDEFRAG) uses when working on an index.

o   20 – a page pre-allocated as part of a bulk load operation, which will eventually be formatted as a ‘real’ page.

 

 

 

 

 

 

 

 

參考資料：

 

http://blog.csdn.net/sqlserverdiscovery/article/details/13291629

https://www.sqlskills.com/blogs/paul/inside-the-storage-engine-anatomy-of-a-page/