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sys.dm_tran_current_transaction (Transact-SQL)

Returns a single row that displays the state information of the transaction in the current session.

Applies to: SQL Server (SQL Server 2008 through current version).

sys.dm_tran_current_transaction

Column name

Data type

Description

transaction_id

bigint

Transaction ID of the current snapshot.

transaction_sequence_num

bigint

Sequence number of the transaction that generates the record version.

transaction_is_snapshot

bit

Snapshot isolation state. This value is 1 if the transaction is started under snapshot isolation. Otherwise, the value is 0.

first_snapshot_sequence_num

bigint

Lowest transaction sequence number of the transactions that were active when a snapshot was taken. On execution, a snapshot transaction takes a snapshot of all of the active transactions at that time. For nonsnapshot transactions, this column shows 0.

last_transaction_sequence_num

bigint

Global sequence number. This value represents the last transaction sequence number that was generated by the system.

first_useful_sequence_num

bigint

Global sequence number. This value represents the oldest transaction sequence number of the transaction that has row versions that must be retained in the version store. Row versions that were created by prior transactions can be removed.

Requires VIEW SERVER STATE permission on the server.

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 within the scope of each transaction.

SELECT 
    transaction_id
   ,transaction_sequence_num
   ,transaction_is_snapshot
   ,first_snapshot_sequence_num
   ,last_transaction_sequence_num
   ,first_useful_sequence_num
  FROM sys.dm_tran_current_transaction;

Here is the result for XSN-59.

transaction_id       transaction_sequence_num transaction_is_snapshot
-------------------- ------------------------ -----------------------
9387                 59                       1                       

first_snapshot_sequence_num last_transaction_sequence_num
--------------------------- -----------------------------
57                               61                      

first_useful_sequence_num
-------------------------
57

The output shows that XSN-59 is a snapshot transaction that uses XSN-57 as the first transaction that was active when XSN-59 started. This means that XSN-59 reads data committed by transactions that have a transaction sequence number lower than XSN-57.

Here is the result for XSN-57.

transaction_id       transaction_sequence_num transaction_is_snapshot
-------------------- ------------------------ -----------------------
9295                 57                       0

first_snapshot_sequence_num last_transaction_sequence_num
--------------------------- -----------------------------
NULL                        61

first_useful_sequence_num
-------------------------
57

Because XSN-57 is not a snapshot transaction, first_snapshot_sequence_num is NULL.

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