Hi,
While you are using your program which is connected to SQL Server database, you can feel slowness on application related with SQL Server database. This problem is probably related with blocking session and database lock.
To find blocking sessions or queries, execute following script. If blocking query are not ended in a short time, you can kill it after asking customer.
SELECT db.name DBName, tl.request_session_id, wt.blocking_session_id, OBJECT_NAME(p.OBJECT_ID) BlockedObjectName, tl.resource_type, h1.TEXT AS RequestingText, h2.TEXT AS BlockingTest, tl.request_mode FROM sys.dm_tran_locks AS tl INNER JOIN sys.databases db ON db.database_id = tl.resource_database_id INNER JOIN sys.dm_os_waiting_tasks AS wt ON tl.lock_owner_address = wt.resource_address INNER JOIN sys.partitions AS p ON p.hobt_id = tl.resource_associated_entity_id INNER JOIN sys.dm_exec_connections ec1 ON ec1.session_id = tl.request_session_id INNER JOIN sys.dm_exec_connections ec2 ON ec2.session_id = wt.blocking_session_id CROSS APPLY sys.dm_exec_sql_text(ec1.most_recent_sql_handle) AS h1 CROSS APPLY sys.dm_exec_sql_text(ec2.most_recent_sql_handle) AS h2 GO
Do you want to learn Microsoft SQL Server DBA Tutorials for Beginners, then read the following articles.
https://ittutorial.org/sql-server-tutorials-microsoft-database-for-beginners/