Streamingondersteuning voor SqlClient
Streaming-ondersteuning tussen SQL Server en een toepassing (nieuw in .NET Framework 4.5) ondersteunt ongestructureerde gegevens op de server (documenten, afbeeldingen en mediabestanden). Een SQL Server-database kan binaire grote objecten (BLOBs) opslaan, maar het ophalen van BLOBS kan veel geheugen gebruiken.
Streaming-ondersteuning van en naar SQL Server vereenvoudigt het schrijven van toepassingen die gegevens streamen, zonder dat de gegevens volledig in het geheugen hoeven te worden geladen, wat resulteert in minder uitzonderingen voor geheugenoverloop.
Met streamingondersteuning kunnen toepassingen in de middelste laag ook beter worden geschaald, met name in scenario's waarin zakelijke objecten verbinding maken met SQL Azure om grote BLOBS te verzenden, op te halen en te bewerken.
Waarschuwing
Asynchrone aanroepen worden niet ondersteund als een toepassing ook het Context Connection trefwoord verbindingsreeks gebruikt.
De leden die zijn toegevoegd ter ondersteuning van streaming, worden gebruikt om gegevens op te halen uit query's en parameters door te geven aan query's en opgeslagen procedures. De streamingfunctie heeft betrekking op basisscenario's voor OLTP en gegevensmigratie en is van toepassing op on-premises en off-premises gegevensmigratieomgevingen.
Streamingondersteuning van SQL Server
Streaming-ondersteuning van SQL Server introduceert nieuwe functionaliteit in en DbDataReader in de SqlDataReader klassen om objecten op te halen StreamXmlReaderTextReader en erop te reageren. Deze klassen worden gebruikt om gegevens op te halen uit query's. Hierdoor is streamingondersteuning van SQL Server gericht op OLTP-scenario's en van toepassing op on-premises en off-premises omgevingen.
De volgende leden zijn toegevoegd om SqlDataReader streaming-ondersteuning van SQL Server in te schakelen:
De volgende leden zijn toegevoegd om DbDataReader streaming-ondersteuning van SQL Server in te schakelen:
Streaming-ondersteuning voor SQL Server
Streaming-ondersteuning voor SQL Server introduceert nieuwe functionaliteit in de SqlParameter klasse, zodat deze kan accepteren en reageren op XmlReader, Streamen TextReader objecten. SqlParameter wordt gebruikt om parameters door te geven aan query's en opgeslagen procedures.
Het verwijderen van een SqlCommand object of aanroepen Cancel moet een streamingbewerking annuleren. Als een toepassing verzendt CancellationToken, wordt annulering niet gegarandeerd.
De volgende SqlDbType typen accepteren een Value van Stream:
- Binair
- VarBinary
De volgende SqlDbType typen accepteren een Value van TextReader:
- Char
- NChar
- NVarChar
- XML
Het XML-typeSqlDbType accepteert een Value van XmlReader.
SqlValue kan waarden van het type XmlReaderaccepteren, TextReaderen Stream.
De XmlReader, TextReaderen Stream het object worden overgebracht naar de waarde die is gedefinieerd door de Size.
Voorbeeld: Streamen vanuit SQL Server
Gebruik de volgende Transact-SQL om de voorbeelddatabase te maken:
CREATE DATABASE [Demo]
GO
USE [Demo]
GO
CREATE TABLE [Streams] (
[id] INT PRIMARY KEY IDENTITY(1, 1),
[textdata] NVARCHAR(MAX),
[bindata] VARBINARY(MAX),
[xmldata] XML)
GO
INSERT INTO [Streams] (textdata, bindata, xmldata) VALUES (N'This is a test', 0x48656C6C6F, N'<test>value</test>')
INSERT INTO [Streams] (textdata, bindata, xmldata) VALUES (N'Hello, World!', 0x54657374696E67, N'<test>value2</test>')
INSERT INTO [Streams] (textdata, bindata, xmldata) VALUES (N'Another row', 0x666F6F626172, N'<fff>bbb</fff><fff>bbc</fff>')
GO
In het voorbeeld ziet u hoe u het volgende doet:
- Vermijd het blokkeren van een gebruikersinterfacethread door een asynchrone manier te bieden om grote bestanden op te halen.
- Een groot tekstbestand overdragen van SQL Server in .NET Framework 4.5.
- Een groot XML-bestand overdragen van SQL Server in .NET Framework 4.5.
- Gegevens ophalen uit SQL Server.
- Draag grote bestanden (BLOBs) over van de ene SQL Server-database naar de andere zonder dat er onvoldoende geheugen beschikbaar is.
using System;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Threading.Tasks;
using System.Xml;
namespace StreamingFromServer {
class Program {
private const string connectionString = @"...";
static void Main(string[] args) {
CopyBinaryValueToFile().Wait();
PrintTextValues().Wait();
PrintXmlValues().Wait();
PrintXmlValuesViaNVarChar().Wait();
Console.WriteLine("Done");
}
// Retrieve a large BLOB from SQL Server in .NET Framework 4.5 using the asynchronous capability.
private static async Task CopyBinaryValueToFile() {
string filePath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "binarydata.bin");
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
using (SqlCommand command = new SqlCommand("SELECT [bindata] FROM [Streams] WHERE [id]=@id", connection)) {
command.Parameters.AddWithValue("id", 1);
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire BLOB into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess)) {
if (await reader.ReadAsync()) {
if (!(await reader.IsDBNullAsync(0))) {
using (FileStream file = new FileStream(filePath, FileMode.Create, FileAccess.Write)) {
using (Stream data = reader.GetStream(0)) {
// Asynchronously copy the stream from the server to the file we just created.
await data.CopyToAsync(file);
}
}
}
}
}
}
}
}
// Transfer a large Text File from SQL Server in .NET Framework 4.5.
private static async Task PrintTextValues() {
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
using (SqlCommand command = new SqlCommand("SELECT [id], [textdata] FROM [Streams]", connection)) {
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire text document into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess)) {
while (await reader.ReadAsync()) {
Console.Write("{0}: ", reader.GetInt32(0));
if (await reader.IsDBNullAsync(1)) {
Console.Write("(NULL)");
}
else {
char[] buffer = new char[4096];
int charsRead = 0;
using (TextReader data = reader.GetTextReader(1)) {
do {
// Grab each chunk of text and write it to the console.
// If you are writing to a TextWriter, you should use WriteAsync or WriteLineAsync.
charsRead = await data.ReadAsync(buffer, 0, buffer.Length);
Console.Write(buffer, 0, charsRead);
} while (charsRead > 0);
}
}
Console.WriteLine();
}
}
}
}
}
// Transfer a large Xml Document from SQL Server in .NET Framework 4.5.
private static async Task PrintXmlValues() {
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
using (SqlCommand command = new SqlCommand("SELECT [id], [xmldata] FROM [Streams]", connection)) {
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire Xml Document into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess)) {
while (await reader.ReadAsync()) {
Console.WriteLine("{0}: ", reader.GetInt32(0));
if (await reader.IsDBNullAsync(1)) {
Console.WriteLine("\t(NULL)");
}
else {
using (XmlReader xmlReader = reader.GetXmlReader(1)) {
int depth = 1;
// NOTE: The XmlReader returned by GetXmlReader does NOT support async operations.
// See the example below (PrintXmlValuesViaNVarChar) for how to get an XmlReader with asynchronous capabilities.
while (xmlReader.Read()) {
switch (xmlReader.NodeType) {
case XmlNodeType.Element:
Console.WriteLine("{0}<{1}>", new string('\t', depth), xmlReader.Name);
depth++;
break;
case XmlNodeType.Text:
Console.WriteLine("{0}{1}", new string('\t', depth), xmlReader.Value);
break;
case XmlNodeType.EndElement:
depth--;
Console.WriteLine("{0}</{1}>", new string('\t', depth), xmlReader.Name);
break;
}
}
}
}
}
}
}
}
}
// Transfer a large Xml Document from SQL Server in .NET Framework 4.5.
// This goes via NVarChar and TextReader to enable asynchronous reading.
private static async Task PrintXmlValuesViaNVarChar() {
XmlReaderSettings xmlSettings = new XmlReaderSettings() {
// Async must be explicitly enabled in the XmlReaderSettings otherwise the XmlReader will throw exceptions when async methods are called.
Async = true,
// Since we will immediately wrap the TextReader we are creating in an XmlReader, we will permit the XmlReader to take care of closing\disposing it.
CloseInput = true,
// If the Xml you are reading is not a valid document (as per <https://learn.microsoft.com/previous-versions/dotnet/netframework-4.0/6bts1x50(v=vs.100)>) you will need to set the conformance level to Fragment.
ConformanceLevel = ConformanceLevel.Fragment
};
using (SqlConnection connection = new SqlConnection(connectionString)) {
await connection.OpenAsync();
// Cast the XML into NVarChar to enable GetTextReader - trying to use GetTextReader on an XML type will throw an exception.
using (SqlCommand command = new SqlCommand("SELECT [id], CAST([xmldata] AS NVARCHAR(MAX)) FROM [Streams]", connection)) {
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire Xml Document into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess)) {
while (await reader.ReadAsync()) {
Console.WriteLine("{0}:", reader.GetInt32(0));
if (await reader.IsDBNullAsync(1)) {
Console.WriteLine("\t(NULL)");
}
else {
// Grab the row as a TextReader, then create an XmlReader on top of it.
// The code doesn't keep a reference to the TextReader since the XmlReader is created with the "CloseInput" setting (so it will close the TextReader when needed).
using (XmlReader xmlReader = XmlReader.Create(reader.GetTextReader(1), xmlSettings)) {
int depth = 1;
// The XmlReader above now supports asynchronous operations, so we can use ReadAsync here.
while (await xmlReader.ReadAsync()) {
switch (xmlReader.NodeType) {
case XmlNodeType.Element:
Console.WriteLine("{0}<{1}>", new string('\t', depth), xmlReader.Name);
depth++;
break;
case XmlNodeType.Text:
// Depending on what your data looks like, you should either use Value or GetValueAsync.
// Value has less overhead (since it doesn't create a Task), but it may also block if additional data is required.
Console.WriteLine("{0}{1}", new string('\t', depth), await xmlReader.GetValueAsync());
break;
case XmlNodeType.EndElement:
depth--;
Console.WriteLine("{0}</{1}>", new string('\t', depth), xmlReader.Name);
break;
}
}
}
}
}
}
}
}
}
}
}
Voorbeeld: Streamen naar SQL Server
Gebruik de volgende Transact-SQL om de voorbeelddatabase te maken:
CREATE DATABASE [Demo2]
GO
USE [Demo2]
GO
CREATE TABLE [BinaryStreams] (
[id] INT PRIMARY KEY IDENTITY(1, 1),
[bindata] VARBINARY(MAX))
GO
CREATE TABLE [TextStreams] (
[id] INT PRIMARY KEY IDENTITY(1, 1),
[textdata] NVARCHAR(MAX))
GO
CREATE TABLE [BinaryStreamsCopy] (
[id] INT PRIMARY KEY IDENTITY(1, 1),
[bindata] VARBINARY(MAX))
GO
In het voorbeeld ziet u hoe u het volgende doet:
- Een grote BLOB overdragen naar SQL Server in .NET Framework 4.5.
- Een groot tekstbestand overbrengen naar SQL Server in .NET Framework 4.5.
- Gebruik de nieuwe asynchrone functie om een grote BLOB over te dragen.
- Gebruik de nieuwe asynchrone functie en het wachtende trefwoord om een grote BLOB over te dragen.
- De overdracht van een grote BLOB annuleren.
- Stream van de ene SQL Server naar de andere met behulp van de nieuwe asynchrone functie.
using System;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
namespace StreamingToServer {
class Program {
private const string connectionString = @"...";
static void Main(string[] args) {
CreateDemoFiles();
StreamBLOBToServer().Wait();
StreamTextToServer().Wait();
// Create a CancellationTokenSource that will be cancelled after 100ms
// Typically this token source will be cancelled by a user request (e.g. a Cancel button).
CancellationTokenSource tokenSource = new CancellationTokenSource();
tokenSource.CancelAfter(100);
try {
CancelBLOBStream(tokenSource.Token).Wait();
}
catch (AggregateException ex) {
// Cancelling an async operation will throw an exception.
// Since we are using the Task's Wait method, this exception will be wrapped in an AggregateException.
// If you were using the 'await' keyword, the compiler would take care of unwrapping the AggregateException.
// Depending on when the cancellation occurs, you can either get an error from SQL Server or from .Net.
if ((ex.InnerException is SqlException) || (ex.InnerException is TaskCanceledException)) {
// This is an expected exception.
Console.WriteLine("Got expected exception: {0}", ex.InnerException.Message);
}
else {
// Did not expect this exception - rethrow it.
throw;
}
}
Console.WriteLine("Done");
}
// This is used to generate the files which are used by the other sample methods.
private static void CreateDemoFiles() {
Random rand = new Random();
byte[] data = new byte[1024];
rand.NextBytes(data);
using (FileStream file = File.Open("binarydata.bin", FileMode.Create)) {
file.Write(data, 0, data.Length);
}
using (StreamWriter writer = new StreamWriter(File.Open("textdata.txt", FileMode.Create))) {
writer.Write(Convert.ToBase64String(data));
}
}
// Transfer a large BLOB to SQL Server in .NET Framework 4.5.
private static async Task StreamBLOBToServer() {
using (SqlConnection conn = new SqlConnection(connectionString)) {
await conn.OpenAsync();
using (SqlCommand cmd = new SqlCommand("INSERT INTO [BinaryStreams] (bindata) VALUES (@bindata)", conn)) {
using (FileStream file = File.Open("binarydata.bin", FileMode.Open)) {
// Add a parameter which uses the FileStream we just opened
// Size is set to -1 to indicate "MAX".
cmd.Parameters.Add("@bindata", SqlDbType.Binary, -1).Value = file;
// Send the data to the server asynchronously.
await cmd.ExecuteNonQueryAsync();
}
}
}
}
// Transfer a large Text File to SQL Server in .NET Framework 4.5.
private static async Task StreamTextToServer() {
using (SqlConnection conn = new SqlConnection(connectionString)) {
await conn.OpenAsync();
using (SqlCommand cmd = new SqlCommand("INSERT INTO [TextStreams] (textdata) VALUES (@textdata)", conn)) {
using (StreamReader file = File.OpenText("textdata.txt")) {
// Add a parameter which uses the StreamReader we just opened.
// Size is set to -1 to indicate "MAX".
cmd.Parameters.Add("@textdata", SqlDbType.NVarChar, -1).Value = file;
// Send the data to the server asynchronously.
await cmd.ExecuteNonQueryAsync();
}
}
}
}
// Cancel the transfer of a large BLOB.
private static async Task CancelBLOBStream(CancellationToken cancellationToken) {
using (SqlConnection conn = new SqlConnection(connectionString)) {
// We can cancel not only sending the data to the server, but also opening the connection.
await conn.OpenAsync(cancellationToken);
// Artificially delay the command by 100ms.
using (SqlCommand cmd = new SqlCommand("WAITFOR DELAY '00:00:00:100';INSERT INTO [BinaryStreams] (bindata) VALUES (@bindata)", conn)) {
using (FileStream file = File.Open("binarydata.bin", FileMode.Open)) {
// Add a parameter which uses the FileStream we just opened.
// Size is set to -1 to indicate "MAX".
cmd.Parameters.Add("@bindata", SqlDbType.Binary, -1).Value = file;
// Send the data to the server asynchronously.
// Pass the cancellation token such that the command will be cancelled if needed.
await cmd.ExecuteNonQueryAsync(cancellationToken);
}
}
}
}
}
}
Voorbeeld: Streamen van de ene SQL-server naar een andere SQL-server
In dit voorbeeld ziet u hoe u asynchroon een grote BLOB van de ene SQL Server naar de andere streamt, met ondersteuning voor annulering.
using System;
using System.Data;
using System.Data.SqlClient;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
namespace StreamingFromServerToAnother {
class Program {
private const string connectionString = @"...";
static void Main(string[] args) {
// For this example, we don't want to cancel,
// so pass in a "blank" cancellation token.
E2EStream(CancellationToken.None).Wait();
Console.WriteLine("Done");
}
// Streaming from one SQL Server to Another One using the new Async.NET.
private static async Task E2EStream(CancellationToken cancellationToken) {
using (SqlConnection readConn = new SqlConnection(connectionString)) {
using (SqlConnection writeConn = new SqlConnection(connectionString)) {
// Note that we are using the same cancellation token for calls to both connections\commands.
// Also we can start both the connection opening asynchronously, and then wait for both to complete.
Task openReadConn = readConn.OpenAsync(cancellationToken);
Task openWriteConn = writeConn.OpenAsync(cancellationToken);
await Task.WhenAll(openReadConn, openWriteConn);
using (SqlCommand readCmd = new SqlCommand("SELECT [bindata] FROM [BinaryStreams]", readConn)) {
using (SqlCommand writeCmd = new SqlCommand("INSERT INTO [BinaryStreamsCopy] (bindata) VALUES (@bindata)", writeConn)) {
// Add an empty parameter to the write command which will be used for the streams we are copying.
// Size is set to -1 to indicate "MAX".
SqlParameter streamParameter = writeCmd.Parameters.Add("@bindata", SqlDbType.Binary, -1);
// The reader needs to be executed with the SequentialAccess behavior to enable network streaming.
// Otherwise ReadAsync will buffer the entire BLOB into memory which can cause scalability issues or even OutOfMemoryExceptions.
using (SqlDataReader reader = await readCmd.ExecuteReaderAsync(CommandBehavior.SequentialAccess, cancellationToken)) {
while (await reader.ReadAsync(cancellationToken)) {
// Grab a stream to the binary data in the source database.
using (Stream dataStream = reader.GetStream(0)) {
// Set the parameter value to the stream source that was opened.
streamParameter.Value = dataStream;
// Asynchronously send data from one database to another.
await writeCmd.ExecuteNonQueryAsync(cancellationToken);
}
}
}
}
}
}
}
}
}
}