A transaction is a single unit of work. If a transaction is successful, all of the data modifications made during the transaction are committed and become a permanent part of the database.
Some times, if there are any issues we will get into this deadlock stage and we don't get any responses from database. In those cases, if you want know what are active connections going on at that point of time, will help identifying issue.
if you want to know more details about active sessions like session ID, Host Name, Login Name, Transaction ID, Transaction Name, Transaction Begin Time,Database ID,Database Name etc.
Use the below query for details,
SELECT
trans.session_id AS [SESSION ID],
execSession.host_name AS [HOST NAME],login_name AS [Login NAME],
trans.transaction_id AS [TRANSACTION ID],
tas.name AS [TRANSACTION NAME],tas.transaction_begin_time AS [TRANSACTION
BEGIN TIME],
tds.database_id AS [DATABASE ID],DBs.name AS [DATABASE NAME]
FROM sys.dm_tran_active_transactions tas
JOIN sys.dm_tran_session_transactions trans
ON (trans.transaction_id=tas.transaction_id)
LEFT OUTER JOIN sys.dm_tran_database_transactions tds
ON (tas.transaction_id = tds.transaction_id )
LEFT OUTER JOIN sys.databases AS DBs
ON tds.database_id = DBs.database_id
LEFT OUTER JOIN sys.dm_exec_sessions AS execSession
ON trans.session_id = execSession.session_id
WHERE execSession.session_id IS NOT NULL
