sys.dm_tran_version_store (Transact-SQL)

Artykuł
12/08/2014

Returns a virtual table that displays all version records in the version store. sys.dm_tran_version_store is inefficient to run because it queries the entire version store, and the version store can be very large.

Each versioned record is stored as binary data together with some tracking or status information. Similar to records in database tables, version-store records are stored in 8192-byte pages. If a record exceeds 8192 bytes, the record will be split across two different records.

Because the versioned record is stored as binary, there are no problems with different collations from different databases. Use sys.dm_tran_version_store to find the previous versions of the rows in binary representation as they exist in the version store.

Składnia

sys.dm_tran_version_store

Table Returned

Column name	Data type	Description
transaction_sequence_num	bigint	Sequence number of the transaction that generates the record version.
version_sequence_num	bigint	Version record sequence number. This value is unique within the version-generating transaction.
database_id	int	Database ID of the versioned record.
rowset_id	bigint	Rowset ID of the record.
status	tinyint	Indicates whether a versioned record has been split across two records. If the value is 0, the record is stored in one page. If the value is 1, the record is split into two records that are stored on two different pages.
min_length_in_bytes	smallint	Minimum length of the record in bytes.
record_length_first_part_in_bytes	smallint	Length of the first part of the versioned record in bytes.
record_image_first_part	varbinary(8000)	Binary image of the first part of version record.
record_length_second_part_in_bytes	smallint	Length of the second part of version record in bytes.
record_image_second_part	varbinary(8000)	Binary image of the second part of the version record.

Permissions

Requires VIEW SERVER STATE permission on the server.

To view the record_image_first_part and record_image_second_part columns, requires CONTROL SERVER permission. Otherwise, these columns will return NULL.

Examples

The following example uses a test scenario in which four concurrent transactions, each identified by a transaction sequence number (XSN), are running in a database that has the ALLOW_SNAPSHOT_ISOLATION and READ_COMMITTED_SNAPSHOT options set to ON. The following transactions are running:

XSN-57 is an update operation under serializable isolation.
XSN-58 is the same as XSN-57.
XSN-59 is a select operation under snapshot isolation.
XSN-60 is the same as XSN-59.

The following query is executed.

SELECT
    transaction_sequence_num,
    version_sequence_num,
    database_id rowset_id,
    status,
    min_length_in_bytes,
    record_length_first_part_in_bytes,
    record_image_first_part,
    record_length_second_part_in_bytes,
    record_image_second_part
  FROM sys.dm_tran_version_store;

Here is the result set.

transaction_sequence_num version_sequence_num database_id
------------------------ -------------------- -----------
57                      1                    9           
57                      2                    9           
57                      3                    9           
58                      1                    9           

rowset_id            status min_length_in_bytes
-------------------- ------ -------------------
72057594038321152    0      12                 
72057594038321152    0      12                 
72057594038321152    0      12                 
72057594038386688    0      16                 

record_length_first_part_in_bytes
---------------------------------
29                               
29                               
29                               
33                               

record_image_first_part                                             
--------------------------------------------------------------------
0x50000C0073000000010000000200FCB000000001000000270000000000        
0x50000C0073000000020000000200FCB000000001000100270000000000        
0x50000C0073000000030000000200FCB000000001000200270000000000        
0x500010000100000002000000030000000300F800000000000000002E0000000000

record_length_second_part_in_bytes record_image_second_part
---------------------------------- ------------------------
0                                  NULL
0                                  NULL
0                                  NULL
0                                  NULL

The output shows that XSN-57 has created three row versions from one table and XSN-58 has created one row version from another table.

Zobacz także

Odwołanie

Dynamic Management Views and Functions (Transact-SQL)

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