How to check how many open transaction is running.

select 

    [s_tst].[session_id],

[s_es].[login_name] as [Login Name],

DB_NAME (s_tdt.database_id) as [Database],

[s_tdt].[database_transaction_begin_time] as [Begin time],

[s_tdt].[database_transaction_log_bytes_used] as [Log Bytes],

[s_tdt].[database_transaction_log_bytes_reserved] as [Log rsvd],

[s_est].text as [Last T- SQL Text],

[s_eqp].[query_plan] as [Last Plan]

From 

sys.dm_tran_database_transactions [s_tdt]

Join

sys.dm_tran_session_transactions [s_tst]

On

[s_tst].[transaction_id]=[s_tdt].[transaction_id]

join

sys.[dm_exec_sessions] [s_es]

On

[s_es].[session_id]= [s_tst].[session_id]

join

sys.dm_exec_connections [s_ec]

On 

[s_ec].[session_id]=[s_tst].[session_id]

Left outer join

sys.dm_exec_requests [s_er]

On 

[s_er].[session_id] = [s_tst].[session_id]

cross apply

sys.dm_exec_sql_text ([s_ec].[most_recent_sql_handle]) as [s_est]

Outer apply

sys.dm_exec_query_plan ([s_er].[plan_handle]) as [s_eqp]

Order by

[Begin Time] Asc