All we need is an easy explanation of the problem, so here it is.
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
How to solve :
I know you bored from this bug, So we are here to help you! Take a deep breath and look at the explanation of your problem. We have many solutions to this problem, But we recommend you to use the first method because it is tested & true method that will 100% work for you.
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.
Note: Use and implement method 1 because this method fully tested our system.
Thank you 🙂