Sql-server – does SELECT with implicit transaction prevent VersionStore cleanup

jdbcsql servertempdbtempdb-version-storetransaction

The JDBC driver usually sets the implicit transaction on in every query executed by the client.
I found many SELECT statements in suspended state with implicit transaction set to ON using Version Store for 48 hour.

These selects statements didn't take up much tempdb space, but I was wondering if this might have blocked version cleanup even though the UPDATE / DELETE / INSERT statements that generated the version store rows had already been committed. (many databases use read committed snapshot isolation level)

After I killed the sessions the version store space became free.

I found the select statement using the version store with the following query:

SELECT 
       db_name(spu.database_id) as database_name,
       ast.session_id, 
       ast.transaction_id, 
       ast.transaction_sequence_num, 
       ast.elapsed_time_seconds,
       b.program_name, 
       b.open_tran, 
       b.status,
       ses.row_count,
       (spu.user_objects_alloc_page_count * 8) AS user_objects_kb,
       (spu.user_objects_dealloc_page_count * 8) AS user_objects_deallocated_kb,
       (spu.internal_objects_alloc_page_count * 8) AS internal_objects_kb,
       (spu.internal_objects_dealloc_page_count * 8) AS internal_objects_deallocated_kb,
       loginame,
       last_request_start_time,
       last_request_end_time,
       cmd,
       lastwaittype
   FROM sys.dm_tran_active_snapshot_database_transactions ast
      JOIN sys.dm_exec_sessions ses ON ses.session_id = ast.session_id
      JOIN sys.dm_db_session_space_usage spu ON spu.session_id = ses.session_id
      JOIN sys.sysprocesses b on ast.session_id = b.spid
   ORDER BY elapsed_time_seconds DESC

Best Answer

I found the answer in this video:
Monitoring Snapshot Isolation with Perfmon in SQL Server

And yes SELECT statements with open transaction can block version store cleanup.

Related Question