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Find the oldest open transaction (ACTIVE_TRANSACTION)

SQL ServerBackup & Log

Command

USE [Customer];
DBCC OPENTRAN;

-- Detailed: show long-running open transactions and their owners:
SELECT s.session_id, s.login_name, s.host_name, s.program_name,
       t.transaction_id,
       DATEDIFF(SECOND, t.transaction_begin_time, GETDATE()) AS duration_sec,
       t.transaction_begin_time
FROM   sys.dm_tran_active_transactions t
  JOIN sys.dm_tran_session_transactions st ON st.transaction_id = t.transaction_id
  JOIN sys.dm_exec_sessions s ON s.session_id = st.session_id
ORDER BY t.transaction_begin_time;

What it does

Shows the oldest open (not committed/rolled back) transaction and the session holding it. An open transaction prevents log truncation (LOG_REUSE_WAIT = ACTIVE_TRANSACTION).

When to use it

To find the root cause when the log does not shrink despite log backups and log_reuse_wait_desc = ACTIVE_TRANSACTION.

Caution

Confirm with the business owner before KILLing the session holding a long open transaction; the rollback may take a long time. Query only; no risk.

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