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Optimizing database access and diving into.Net SqlClient Mladen Prajdić SQL Server

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Presentation on theme: "Optimizing database access and diving into.Net SqlClient Mladen Prajdić SQL Server"— Presentation transcript:

1 Optimizing database access and diving into.Net SqlClient Mladen Prajdić SQL Server

2 About me Welcome to Slovenia The sunny side of Alps

3 Disclaimer I use SELECT * in demos only for brevity

4 Agenda Building foundation... Client Data Access New exciting stuff! Async SqlDataReader Consistency is the key! TransactionScope Reduce, Reuse, Recycle! Connection Pooling Make it go faster! Batching Commands What’s it doing? Statistics Multiple interleaves? MARS

5 Correct Connection Use using (SqlConnection conn = new SqlConnection(_connString)) { conn.Open(); // db access code here // return data reader or objects }

6 Client Data Access Building the foundation...

7 TDS Data Flow Result set “Done” token Result set “Done” token Result set “Done” token using (SqlCommand cmd = new SqlCommand("SELECT * FROM Table1; SELECT * FROM Table2", conn)) { SqlDataReader rdr = cmd.ExecuteReader(CommandBehavior.CloseConnection); // return the list of data objects return CreateListOfBusinessObjects(rdr); // or return the SqlDataReader itself return rdr; }

8 TDS Data Flow Result set “Done” token Row Data “Row” token Row Data “Row” token Row Data “Row” token Result set “Done” token Result set “Done” token

9 TDS Data Flow Result set “Done” token Row Data “Row” token Row Data “Row” token Row Data “Row” token Result set “Done” token Result set “Done” token Column Data Column Header Column Data Column Header Column Data Column Header Small datatype INTMedium datatype CHAR(50)Large datatype NVARCHAR(MAX)

10 SqlDataReader Data Access Default access (Non-Sequential) Sequential access // default = non-sequential access var rdr = cmd.ExecuteReader(); // sequential access var rdr = cmd.ExecuteReader(CommandBehavior.SequentialAccess);

11 Non-Sequential (Default) Access Column Data Column Header Column Data Column Header Column Data Column Header 012 Column Data Column Header Column Data Column Header Column Data Column Header 0 12 We can go back and read all previous columns’ data

12 Non-Sequential (Default) Access The full row is stored in client memory Move back and forward in the row Possible scalability issues Possible Out of Memory exceptions

13 Sequential Access Column Data Column Header Column Data Column Header Column Data Column Header 012 Column Data Column Header Column Data Column Header Column Data Column Header 0 12 Forward reading only. Trying to go back throws an error. ERROR

14 Sequential Access Only the current value is stored in client memory Move only forward in the row Get* methods for getting data GetBytes, GetChars for BLOBs Save to a stream by reading it in chunks // get first column value that is int rdr.GetInt32(0); // get second column value that is binary byte[] buffer = new byte[100]; // loop this to get the whole column out in chunks rdr.GetBytes(0, 100, buffer, 0, buffer.Length); // save the byte buffer to file or something

15 Sequential Access Full streaming support in.Net 4.5 GetStream, GetTextReader, GetXmlReader No more chunking

16 Sequential Access SqlCommand readCmd = // get varbinary(MAX) from source table new SqlCommand("SELECT BinData FROM Source", readConn); SqlCommand writeCmd = // insert varbinary(MAX) into target table new SqlCommand("INSERT INTO Target(BinData) VALUES writeConn); // Size is set to -1 to indicate "MAX" SqlParameter streamParameter = SqlDbType.Binary, -1); SqlDataReader readerSource = readCmd.ExecuteReader(CommandBehavior.SequentialAccess); while (readerSource.Read()) { // Grab a stream to the binary data in the source database Stream dataStream = readerSource.GetStream(0); // Set the parameter value to the stream source that was opened streamParameter.Value = dataStream; // send the data to the target database writeCmd.ExecuteNonQuery(); }

17 Async SqlDataReader New exciting stuff!

18 Old “Run in Background” Ways SqlCommand cmd = new SqlCommand("SELECT * FROM Table", conn); // either this or a background worker IAsyncResult result = cmd.BeginExecuteReader(); // for the reader to complete while (!result.IsCompleted) { // do UI operations without problems } using (SqlDataReader reader = cmd.EndExecuteReader(result)) { // show reader results ShowDbOperationResult(reader); }

20 What is it good for? Make code async without complex threading code No threads created by default Use default for IO-bound workload Use Task.Run to create background thread for CPU- bound workload Supported by Entity Framework 6 For more in depth details on this, search for “Asynchronous Programming with Async and Await”

21 What to use when? Prefer NextResultAsync in either access modes TDS tokens between result sets are processed in async Result set TDS Tokens Async Result set TDS Tokens Async Result set

22 What to use when? Prefer ReadAsync in either access modes TDS tokens between multiple packets are processed in async Data Packet TDS Tokens Async Data Packet TDS Tokens Async Data Packet Single Row

23 What to use when? Use IsDBNull and GetFieldValue If ReadAsync() in Default (Non-Sequential) mode Since data is already in the client buffer IsDBNullAsync and GetFieldValueAsync Sequential mode target column is large needed to read past large columns rdr.GetStream(i).CopyToAsync(outputStream) for huge columns in Sequential mode

24 DEMO

25 TransactionScope Consistency is the key!

26 TransactionScope using (TransactionScope txScope = new TransactionScope()) { using (SqlConnection conn2012AW = new SqlConnection(_connString2012AW)) { // do stuff } txScope.Complete(); }

27 TransactionScope Easy to use Keeps code simple Great transaction management out of the box MSTDC escalation Always, unless connecting to the same database with non concurrent connections sys.dm_tran_active_transactions.transaction_uow Default isolation level is SERIALIZABLE

28 DEMO

29 Connection Pooling Reduce, Reuse, Recycle!

30 Connection Pooling Connection pools created per process per application domain per connection string per Windows identity (if integrated security) Default max pool size = 100 Audit Login, Audit Logout Events EventSubClass 1 = Nonpooled 2 = Pooled

31 Connection Pooling Resets sp_reset_connection Resets the connection for reuse A long list of what it does on the next slide for reference Does NOT reset the isolation level Always explicitly specify the isolation level

32 Connection Pooling Resets All error states and numbers (like Stops all EC's (execution contexts) that are child threads of a parent EC executing a parallel query Waits for any outstanding I/O operations that is outstanding Frees any held buffers on the server by the connection Unlocks any buffer resources that are used by the connection Releases all allocated memory owned by the connection Clears any work or temporary tables that are created by the connection Kills all global cursors owned by the connection Closes any open SQL-XML handles that are open Deletes any open SQL-XML related work tables Closes all system tables Closes all user tables Drops all temporary objects Aborts open transactions Defects from a distributed transaction when enlisted Decrements the reference count for users in current database which releases shared database locks Frees acquired locks Releases any acquired handles Resets all SET options to the default values Resets the value Resets the value Resets any session level trace options using dbcc traceon()

33 DEMO

34 Batching Commands Make it go faster!

35 Batching Commands Optimizing network round trips Consider Bulk Insert if possible Streaming data insert SqlBulkCopy Class 10k inserts = 10k round trips 1000 x 10 batches = 10 round trips 1000 CSV SQL statements in one command Or… a hidden gem

36 DEMO

37 Statistics What’s it doing?

38 Client Statistics Enable per connection Cumulative Good for tracking the actual db access from app Save to a queue, process off-peak Analyze historical access data

39 DEMO

40 MARS Multiple interleaves?

41 Multiple Active Result Sets (MARS) Statement multiplexing/interleaving SELECT, FETCH RECEIVE, READTEXT BULK INSERT / BCP Other statements must complete Transaction savepoints aren’t allowed Usually used for SELECT N+1 scenarios

42 DEMO

43 ?

44


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