Today, we got a service request that our customer reported that the using the following article the blocker and blocked queries haven't relation between them.
In this post we are going to explain why?. Normally, when you need to identify blocking issues we’re used to run the following query explained on this URL.
select conn.session_id as blockerSession,conn2.session_id as BlockedSession,req.wait_time as Waiting_Time_ms,cast((req.wait_time/1000.) as decimal(18,2)) as Waiting_Time_secs, cast((req.wait_time/1000./60.) as decimal(18,2)) as Waiting_Time_mins,t.text as BlockerQuery,t2.text as BlockedQuery, req.wait_type from sys.dm_exec_requests as req inner join sys.dm_exec_connections as conn on req.blocking_session_id=conn.session_id inner join sys.dm_exec_connections as conn2 on req.session_id=conn2.session_id cross apply sys.dm_exec_sql_text(conn.most_recent_sql_handle) as t cross apply sys.dm_exec_sql_text(conn2.most_recent_sql_handle) as t2
We found a situation that the query reported could not be the query that is blocking the another one. In this specify situation is when our customer is running multiple queries in the same transaction:
BEGIN TRANSACTION UPDATE INSERT COMMIT TRANSACTION
11:00 AM Customer open a transaction – BEGIN TRANSACTION
11:01 AM Customer runs INSERT Table1
11:02 AM Customer runs UPDATE Table 2
11:03 AM Customer commit the transaction.
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