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SQL DTC Confusion


SQL DTC Confusion

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SQLSACT
SQLSACT
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Hi All

I am trying to figure out the ins and outs of DTC and how SQL uses it.

Does SQL only ever use DTC when SQL is installed as clustered?

Thanks
Orlando Colamatteo
Orlando Colamatteo
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SQL also will the DTC if you try using explicit transactions with Linked Servers. I also use it with SSIS transactions, not technically the database engine but another use of DTC nonetheless.

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opc.three (2/26/2013)
SQL also will the DTC if you try using explicit transactions with Linked Servers. I also use it with SSIS transactions, not technically the database engine but another use of DTC nonetheless.


Thanks

So even if SQL is installed as non clustered, DTC can still become involved somehow

If that's the case, why when dealing with Clustered instances of SQL Server do we have to explicitly create a DTC component in the Cluster?

Thanks
Orlando Colamatteo
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So even if SQL is installed as non clustered, DTC can still become involved somehow

Yep.

If that's the case, why when dealing with Clustered instances of SQL Server do we have to explicitly create a DTC component in the Cluster?

My understanding is that the Windows cluster relies on it. DTC is not a SQL Server-specific piece of software. It is a stand-alone Windows service that SQL Server sometimes leverages. SQL Server clusters sit on top of Windows clusters, and its the Windows cluster that requires the DTC to be configured.

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Perry Whittle
Perry Whittle
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SQLSACT (2/26/2013)
So even if SQL is installed as non clustered, DTC can still become involved somehow

DTC is not just used for SQL Server, the OS uses it for remote calls too.



SQLSACT (2/26/2013)
If that's the case, why when dealing with Clustered instances of SQL Server do we have to explicitly create a DTC component in the Cluster?

Thanks

In a clustered environment, a clustered DTC is used to recover inflight transactions. Take the following scenario:

Node1 and Node2 have a clustered instance INST1 which is currently active on Node1. DTC is local and not clustered.

A remote transaction is started and during the transaction the instance goes offline and fails over to Node2. The SQL instance is no longer local to the stand alone DTC and cannot connect to recover the inflight transaction.

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SQLSACT
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Thanks Guys - This clears up a lot

Perry, would you say that it's safe to not cluster DTC when you have a single node cluster?

Thanks
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