First published on MSDN on Jan 24, 2012
For some reason I have been looking at DMV output closely the last couple of weeks. I just blogged about the pending I/O requests and now I have a behavior to outline for
dm_tran_session_transactions
for todays blog.
select * from sys.dm_tran_session_transactions
The scenario I was looking at is as follows.
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Server A
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Server B
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Broker calls activation procedure
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Begin Tran (local)
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Linked Server Query
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Transaction Promoted to DTC
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Transaction Imported from Server A
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xp_cmdshell
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Looped back and blocked
Separate Transaction
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Blocking
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The process is based on SQL Service Broker.
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The service broker session on Server A is 20
s
.
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It starts a local transaction and eventually performs a linked server query.
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This causes the transaction to be promoted to a DTC transaction.
At this point in time the *active transaction* DMVs on both Server A and B show the enlisted UOW of the DTC transaction.
That is, except the sys.dm_tran_session_transactions on server A.
After some digging I uncovered that the dm_tran_session_transactions DMV only outputs rows for sessions (
s
) that are NOT system level sessions. Since the broker activity is handled on a system session the DMV will not materialize a row for Session 20
s
on Server A in this example. Instead you have to use the additional *active transaction* tables to track the UOW across this system.
Note:
I am able to use any transaction (local or DTC) as part of SQL Service Broker activation which will not show rows in the session transactions DMV because it is considered a system session.
Bob Dorr - Principal SQL Server Escalation Engineer
