Performance Tuning with SQL Server Dynamic Management Views

FROM dbo.Culture ;
-- COMMIT;
Listing 4.24: Tab 4, a query using READ_COMMITTED_SNAPSHOT isolation.
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Chapter 4: Transactions
So far, the queries return exactly the same results under either SNAPSHOT or READ_
COMMITTED_SNAPSHOT mode. At this point, let's investigate current snapshot activity
using our DMOs. The first simple query we can run is simply to get a count of currently
active snapshots, from the sys.dm_tran_transactions_snapshot DMV, as shown
in Listing 4.25.
SELECT COUNT([transaction_sequence_num]) AS [snapshot transaction count]
FROM sys.dm_tran_transactions_snapshot ;
Listing 4.25: A count of currently active snapshot transactions.
This returns a snapshot transaction count of two, since our SNAPSHOT query in Listing
4.5 relies on the ultimate result of our two open transactions in Listings 4.21 (Tab 1) and
4.22 (Tab 2). Next, let's interrogate the active_snapshot_database_transactions
DMV, as shown in Listing 4.26.
SELECT DTASDT.transaction_id ,
DTASDT.session_id ,
DTASDT.transaction_sequence_num ,
DTASDT.first_snapshot_sequence_num ,
DTASDT.commit_sequence_num ,
DTASDT.is_snapshot ,
DTASDT.elapsed_time_seconds ,
DEST.text AS [command text]
FROM sys.dm_tran_active_snapshot_database_transactions DTASDT
INNER JOIN sys.dm_exec_connections DEC
ON DTASDT.session_id = DEC.most_recent_session_id
INNER JOIN sys.dm_tran_database_transactions DTDT
ON DTASDT.transaction_id = DTDT.transaction_id