Panduan: Menggunakan BatchBlock dan BatchedJoinBlock untuk Meningkatkan Efisiensi
Pustaka Aliran Data TPL menyediakan kelas System.Threading.Tasks.Dataflow.BatchBlock<T> dan System.Threading.Tasks.Dataflow.BatchedJoinBlock<T1,T2> sehingga Anda dapat menerima dan menyangga data dari satu atau beberapa sumber lalu menyebarluaskan data buffer tersebut sebagai satu koleksi. Mekanisme batching ini berguna saat Anda mengumpulkan data dari satu atau beberapa sumber lalu memproses beberapa elemen data sebagai batch. Misalnya, pertimbangkan aplikasi yang menggunakan aliran data untuk menyisipkan rekaman ke dalam database. Operasi ini bisa lebih efisien jika beberapa item dimasukkan pada saat yang sama alih-alih satu per satu secara berurutan. Dokumen ini menjelaskan cara menggunakan kelas BatchBlock<T> untuk meningkatkan efisiensi operasi penyisipan database tersebut. Ini juga menjelaskan cara menggunakan kelas BatchedJoinBlock<T1,T2> untuk mengambil hasil dan pengecualian apa pun yang terjadi saat program membaca dari database.
Catatan
Pustaka Aliran Data TPL (namespace layanan System.Threading.Tasks.Dataflow) tidak didistribusikan dengan .NET. Untuk menginstal namespace layanan System.Threading.Tasks.Dataflow di Visual Studio, buka proyek, pilih Kelola Paket NuGet dari menu Proyek, dan cari paket System.Threading.Tasks.Dataflow secara online. Atau, untuk menginstalnya menggunakan .NET Core CLI, jalankan dotnet add package System.Threading.Tasks.Dataflow.
Prasyarat
Baca bagian Blokir Gabungan di dokumen Aliran Data sebelum Anda memulai panduan ini.
Pastikan Anda memiliki salinan database Northwind, Northwind.sdf, yang tersedia di komputer Anda. File ini biasanya terletak di folder %Program Files%\Microsoft SQL Server Compact Edition\v3.5\Samples\.
Penting
Dalam beberapa versi Windows, Anda tidak dapat tersambung ke Northwind.sdf jika Visual Studio berjalan dalam mode non-administrator. Untuk menyambungkan ke Northwind.sdf, mulai Visual Studio atau Perintah Pengembang untuk Visual Studio dalam mode Jalankan sebagai administrator.
Panduan ini berisi bagian berikut:
Menambah Data Karyawan ke Database tanpa Menggunakan Buffering
Menggunakan Buffering untuk Menambah Data Karyawan ke Database
Menggunakan Gabungan Buffered untuk Membaca Data Karyawan dari Database
Membuat Aplikasi Konsol
Di Visual Studio, buat proyek Visual C# atau Visual Basic Console Application. Dalam dokumen ini, proyek diberi nama
DataflowBatchDatabase.Dalam proyek Anda, tambahkan referensi ke System.Data.SqlServerCe.dll dan referensi ke System.Threading.Tasks.Dataflow.dll.
Pastikan Form1.cs (Form1.vb untuk Visual Basic) berisi pernyataan berikut
using(Importsdalam Visual Basic).using System; using System.Collections.Generic; using System.Data.SqlServerCe; using System.Diagnostics; using System.IO; using System.Threading.Tasks.Dataflow;Imports System.Collections.Generic Imports System.Data.SqlServerCe Imports System.Diagnostics Imports System.IO Imports System.Threading.Tasks.DataflowSilakan tambahkan anggota data berikut ke kelas
Program.// The number of employees to add to the database. // TODO: Change this value to experiment with different numbers of // employees to insert into the database. static readonly int insertCount = 256; // The size of a single batch of employees to add to the database. // TODO: Change this value to experiment with different batch sizes. static readonly int insertBatchSize = 96; // The source database file. // TODO: Change this value if Northwind.sdf is at a different location // on your computer. static readonly string sourceDatabase = @"C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Samples\Northwind.sdf"; // TODO: Change this value if you require a different temporary location. static readonly string scratchDatabase = @"C:\Temp\Northwind.sdf";' The number of employees to add to the database. ' TODO: Change this value to experiment with different numbers of ' employees to insert into the database. Private Shared ReadOnly insertCount As Integer = 256 ' The size of a single batch of employees to add to the database. ' TODO: Change this value to experiment with different batch sizes. Private Shared ReadOnly insertBatchSize As Integer = 96 ' The source database file. ' TODO: Change this value if Northwind.sdf is at a different location ' on your computer. Private Shared ReadOnly sourceDatabase As String = "C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Samples\Northwind.sdf" ' TODO: Change this value if you require a different temporary location. Private Shared ReadOnly scratchDatabase As String = "C:\Temp\Northwind.sdf"
Mendefinisikan Kelas Karyawan
Menambah kelas Employee ke kelas Program.
// Describes an employee. Each property maps to a
// column in the Employees table in the Northwind database.
// For brevity, the Employee class does not contain
// all columns from the Employees table.
class Employee
{
public int EmployeeID { get; set; }
public string LastName { get; set; }
public string FirstName { get; set; }
// A random number generator that helps tp generate
// Employee property values.
static Random rand = new Random(42);
// Possible random first names.
static readonly string[] firstNames = { "Tom", "Mike", "Ruth", "Bob", "John" };
// Possible random last names.
static readonly string[] lastNames = { "Jones", "Smith", "Johnson", "Walker" };
// Creates an Employee object that contains random
// property values.
public static Employee Random()
{
return new Employee
{
EmployeeID = -1,
LastName = lastNames[rand.Next() % lastNames.Length],
FirstName = firstNames[rand.Next() % firstNames.Length]
};
}
}
' Describes an employee. Each property maps to a
' column in the Employees table in the Northwind database.
' For brevity, the Employee class does not contain
' all columns from the Employees table.
Private Class Employee
Public Property EmployeeID() As Integer
Public Property LastName() As String
Public Property FirstName() As String
' A random number generator that helps tp generate
' Employee property values.
Private Shared rand As New Random(42)
' Possible random first names.
Private Shared ReadOnly firstNames() As String = {"Tom", "Mike", "Ruth", "Bob", "John"}
' Possible random last names.
Private Shared ReadOnly lastNames() As String = {"Jones", "Smith", "Johnson", "Walker"}
' Creates an Employee object that contains random
' property values.
Public Shared Function Random() As Employee
Return New Employee With {.EmployeeID = -1, .LastName = lastNames(rand.Next() Mod lastNames.Length), .FirstName = firstNames(rand.Next() Mod firstNames.Length)}
End Function
End Class
Kelas Employee berisi tiga properti, EmployeeID, LastName, dan FirstName. Properti ini sesuai dengan kolom Employee ID, Last Name, dan First Name di dalam tabel Employees di database Northwind. Untuk demonstrasi ini, kelas Employee juga mendefinisikan metode Random, yang membuat objek Employee yang memiliki nilai acak untuk propertinya.
Mendefinisikan Operasi Database Karyawan
Tambahkan ke kelas Program metode InsertEmployees, GetEmployeeCount, dan GetEmployeeID.
// Adds new employee records to the database.
static void InsertEmployees(Employee[] employees, string connectionString)
{
using (SqlCeConnection connection =
new SqlCeConnection(connectionString))
{
try
{
// Create the SQL command.
SqlCeCommand command = new SqlCeCommand(
"INSERT INTO Employees ([Last Name], [First Name])" +
"VALUES (@lastName, @firstName)",
connection);
connection.Open();
for (int i = 0; i < employees.Length; i++)
{
// Set parameters.
command.Parameters.Clear();
command.Parameters.Add("@lastName", employees[i].LastName);
command.Parameters.Add("@firstName", employees[i].FirstName);
// Execute the command.
command.ExecuteNonQuery();
}
}
finally
{
connection.Close();
}
}
}
// Retrieves the number of entries in the Employees table in
// the Northwind database.
static int GetEmployeeCount(string connectionString)
{
int result = 0;
using (SqlCeConnection sqlConnection =
new SqlCeConnection(connectionString))
{
SqlCeCommand sqlCommand = new SqlCeCommand(
"SELECT COUNT(*) FROM Employees", sqlConnection);
sqlConnection.Open();
try
{
result = (int)sqlCommand.ExecuteScalar();
}
finally
{
sqlConnection.Close();
}
}
return result;
}
// Retrieves the ID of the first employee that has the provided name.
static int GetEmployeeID(string lastName, string firstName,
string connectionString)
{
using (SqlCeConnection connection =
new SqlCeConnection(connectionString))
{
SqlCeCommand command = new SqlCeCommand(
string.Format(
"SELECT [Employee ID] FROM Employees " +
"WHERE [Last Name] = '{0}' AND [First Name] = '{1}'",
lastName, firstName),
connection);
connection.Open();
try
{
return (int)command.ExecuteScalar();
}
finally
{
connection.Close();
}
}
}
' Adds new employee records to the database.
Private Shared Sub InsertEmployees(ByVal employees() As Employee, ByVal connectionString As String)
Using connection As New SqlCeConnection(connectionString)
Try
' Create the SQL command.
Dim command As New SqlCeCommand("INSERT INTO Employees ([Last Name], [First Name])" & "VALUES (@lastName, @firstName)", connection)
connection.Open()
For i As Integer = 0 To employees.Length - 1
' Set parameters.
command.Parameters.Clear()
command.Parameters.Add("@lastName", employees(i).LastName)
command.Parameters.Add("@firstName", employees(i).FirstName)
' Execute the command.
command.ExecuteNonQuery()
Next i
Finally
connection.Close()
End Try
End Using
End Sub
' Retrieves the number of entries in the Employees table in
' the Northwind database.
Private Shared Function GetEmployeeCount(ByVal connectionString As String) As Integer
Dim result As Integer = 0
Using sqlConnection As New SqlCeConnection(connectionString)
Dim sqlCommand As New SqlCeCommand("SELECT COUNT(*) FROM Employees", sqlConnection)
sqlConnection.Open()
Try
result = CInt(Fix(sqlCommand.ExecuteScalar()))
Finally
sqlConnection.Close()
End Try
End Using
Return result
End Function
' Retrieves the ID of the first employee that has the provided name.
Private Shared Function GetEmployeeID(ByVal lastName As String, ByVal firstName As String, ByVal connectionString As String) As Integer
Using connection As New SqlCeConnection(connectionString)
Dim command As New SqlCeCommand(String.Format("SELECT [Employee ID] FROM Employees " & "WHERE [Last Name] = '{0}' AND [First Name] = '{1}'", lastName, firstName), connection)
connection.Open()
Try
Return CInt(Fix(command.ExecuteScalar()))
Finally
connection.Close()
End Try
End Using
End Function
Metode InsertEmployees menambahkan catatan karyawan baru ke database. Metode GetEmployeeCount mengambil jumlah entri di dalam tabel Employees. Metode GetEmployeeID mengambil pengidentifikasi karyawan pertama yang memiliki nama yang disediakan. Masing-masing metode ini mengambil string koneksi ke database Northwind dan menggunakan fungsionalitas di namespace System.Data.SqlServerCe untuk berkomunikasi dengan database.
Menambah Data Karyawan ke Database tanpa Menggunakan Buffering
Tambahkan ke kelas Program metode AddEmployees dan PostRandomEmployees.
// Posts random Employee data to the provided target block.
static void PostRandomEmployees(ITargetBlock<Employee> target, int count)
{
Console.WriteLine("Adding {0} entries to Employee table...", count);
for (int i = 0; i < count; i++)
{
target.Post(Employee.Random());
}
}
// Adds random employee data to the database by using dataflow.
static void AddEmployees(string connectionString, int count)
{
// Create an ActionBlock<Employee> object that adds a single
// employee entry to the database.
var insertEmployee = new ActionBlock<Employee>(e =>
InsertEmployees(new Employee[] { e }, connectionString));
// Post several random Employee objects to the dataflow block.
PostRandomEmployees(insertEmployee, count);
// Set the dataflow block to the completed state and wait for
// all insert operations to complete.
insertEmployee.Complete();
insertEmployee.Completion.Wait();
}
' Posts random Employee data to the provided target block.
Private Shared Sub PostRandomEmployees(ByVal target As ITargetBlock(Of Employee), ByVal count As Integer)
Console.WriteLine("Adding {0} entries to Employee table...", count)
For i As Integer = 0 To count - 1
target.Post(Employee.Random())
Next i
End Sub
' Adds random employee data to the database by using dataflow.
Private Shared Sub AddEmployees(ByVal connectionString As String, ByVal count As Integer)
' Create an ActionBlock<Employee> object that adds a single
' employee entry to the database.
Dim insertEmployee = New ActionBlock(Of Employee)(Sub(e) InsertEmployees(New Employee() {e}, connectionString))
' Post several random Employee objects to the dataflow block.
PostRandomEmployees(insertEmployee, count)
' Set the dataflow block to the completed state and wait for
' all insert operations to complete.
insertEmployee.Complete()
insertEmployee.Completion.Wait()
End Sub
Metode AddEmployees menambahkan data karyawan acak ke database dengan menggunakan aliran data. Ini membuat objek ActionBlock<TInput> yang memanggil metode InsertEmployees untuk menambahkan entri karyawan ke database. Metode AddEmployees kemudian memanggil metode PostRandomEmployees untuk memposting beberapa objek Employee ke objek ActionBlock<TInput>. Metode AddEmployees kemudian menunggu semua operasi sisipan selesai.
Menggunakan Buffering untuk Menambah Data Karyawan ke Database
Tambahkan metode AddEmployeesBatched ke kelas Program:
// Adds random employee data to the database by using dataflow.
// This method is similar to AddEmployees except that it uses batching
// to add multiple employees to the database at a time.
static void AddEmployeesBatched(string connectionString, int batchSize,
int count)
{
// Create a BatchBlock<Employee> that holds several Employee objects and
// then propagates them out as an array.
var batchEmployees = new BatchBlock<Employee>(batchSize);
// Create an ActionBlock<Employee[]> object that adds multiple
// employee entries to the database.
var insertEmployees = new ActionBlock<Employee[]>(a =>
InsertEmployees(a, connectionString));
// Link the batch block to the action block.
batchEmployees.LinkTo(insertEmployees);
// When the batch block completes, set the action block also to complete.
batchEmployees.Completion.ContinueWith(delegate { insertEmployees.Complete(); });
// Post several random Employee objects to the batch block.
PostRandomEmployees(batchEmployees, count);
// Set the batch block to the completed state and wait for
// all insert operations to complete.
batchEmployees.Complete();
insertEmployees.Completion.Wait();
}
' Adds random employee data to the database by using dataflow.
' This method is similar to AddEmployees except that it uses batching
' to add multiple employees to the database at a time.
Private Shared Sub AddEmployeesBatched(ByVal connectionString As String, ByVal batchSize As Integer, ByVal count As Integer)
' Create a BatchBlock<Employee> that holds several Employee objects and
' then propagates them out as an array.
Dim batchEmployees = New BatchBlock(Of Employee)(batchSize)
' Create an ActionBlock<Employee[]> object that adds multiple
' employee entries to the database.
Dim insertEmployees = New ActionBlock(Of Employee())(Sub(a) Program.InsertEmployees(a, connectionString))
' Link the batch block to the action block.
batchEmployees.LinkTo(insertEmployees)
' When the batch block completes, set the action block also to complete.
batchEmployees.Completion.ContinueWith(Sub() insertEmployees.Complete())
' Post several random Employee objects to the batch block.
PostRandomEmployees(batchEmployees, count)
' Set the batch block to the completed state and wait for
' all insert operations to complete.
batchEmployees.Complete()
insertEmployees.Completion.Wait()
End Sub
Metode ini mirip AddEmployees, kecuali bahwa metode ini juga menggunakan kelas BatchBlock<T> untuk menyangga beberapa objek Employee sebelum mengirim objek tersebut ke objek ActionBlock<TInput>. Karena kelas BatchBlock<T> menyebarkan beberapa elemen sebagai koleksi, objek ActionBlock<TInput> dimodifikasi untuk bertindak pada array dari objek Employee. Seperti dalam metode AddEmployees, AddEmployeesBatched memanggil metode PostRandomEmployees untuk memposting beberapa objek Employee namun, AddEmployeesBatched memposting objek ini ke objek BatchBlock<T>. Metode AddEmployeesBatched kemudian menunggu semua operasi sisipan selesai.
Menggunakan Gabungan Buffered untuk Membaca Data Karyawan dari Database
Tambahkan metode GetRandomEmployees ke kelas Program.
// Displays information about several random employees to the console.
static void GetRandomEmployees(string connectionString, int batchSize,
int count)
{
// Create a BatchedJoinBlock<Employee, Exception> object that holds
// both employee and exception data.
var selectEmployees = new BatchedJoinBlock<Employee, Exception>(batchSize);
// Holds the total number of exceptions that occurred.
int totalErrors = 0;
// Create an action block that prints employee and error information
// to the console.
var printEmployees =
new ActionBlock<Tuple<IList<Employee>, IList<Exception>>>(data =>
{
// Print information about the employees in this batch.
Console.WriteLine("Received a batch...");
foreach (Employee e in data.Item1)
{
Console.WriteLine("Last={0} First={1} ID={2}",
e.LastName, e.FirstName, e.EmployeeID);
}
// Print the error count for this batch.
Console.WriteLine("There were {0} errors in this batch...",
data.Item2.Count);
// Update total error count.
totalErrors += data.Item2.Count;
});
// Link the batched join block to the action block.
selectEmployees.LinkTo(printEmployees);
// When the batched join block completes, set the action block also to complete.
selectEmployees.Completion.ContinueWith(delegate { printEmployees.Complete(); });
// Try to retrieve the ID for several random employees.
Console.WriteLine("Selecting random entries from Employees table...");
for (int i = 0; i < count; i++)
{
try
{
// Create a random employee.
Employee e = Employee.Random();
// Try to retrieve the ID for the employee from the database.
e.EmployeeID = GetEmployeeID(e.LastName, e.FirstName, connectionString);
// Post the Employee object to the Employee target of
// the batched join block.
selectEmployees.Target1.Post(e);
}
catch (NullReferenceException e)
{
// GetEmployeeID throws NullReferenceException when there is
// no such employee with the given name. When this happens,
// post the Exception object to the Exception target of
// the batched join block.
selectEmployees.Target2.Post(e);
}
}
// Set the batched join block to the completed state and wait for
// all retrieval operations to complete.
selectEmployees.Complete();
printEmployees.Completion.Wait();
// Print the total error count.
Console.WriteLine("Finished. There were {0} total errors.", totalErrors);
}
' Displays information about several random employees to the console.
Private Shared Sub GetRandomEmployees(ByVal connectionString As String, ByVal batchSize As Integer, ByVal count As Integer)
' Create a BatchedJoinBlock<Employee, Exception> object that holds
' both employee and exception data.
Dim selectEmployees = New BatchedJoinBlock(Of Employee, Exception)(batchSize)
' Holds the total number of exceptions that occurred.
Dim totalErrors As Integer = 0
' Create an action block that prints employee and error information
' to the console.
Dim printEmployees = New ActionBlock(Of Tuple(Of IList(Of Employee), IList(Of Exception)))(Sub(data)
' Print information about the employees in this batch.
' Print the error count for this batch.
' Update total error count.
Console.WriteLine("Received a batch...")
For Each e As Employee In data.Item1
Console.WriteLine("Last={0} First={1} ID={2}", e.LastName, e.FirstName, e.EmployeeID)
Next e
Console.WriteLine("There were {0} errors in this batch...", data.Item2.Count)
totalErrors += data.Item2.Count
End Sub)
' Link the batched join block to the action block.
selectEmployees.LinkTo(printEmployees)
' When the batched join block completes, set the action block also to complete.
selectEmployees.Completion.ContinueWith(Sub() printEmployees.Complete())
' Try to retrieve the ID for several random employees.
Console.WriteLine("Selecting random entries from Employees table...")
For i As Integer = 0 To count - 1
Try
' Create a random employee.
Dim e As Employee = Employee.Random()
' Try to retrieve the ID for the employee from the database.
e.EmployeeID = GetEmployeeID(e.LastName, e.FirstName, connectionString)
' Post the Employee object to the Employee target of
' the batched join block.
selectEmployees.Target1.Post(e)
Catch e As NullReferenceException
' GetEmployeeID throws NullReferenceException when there is
' no such employee with the given name. When this happens,
' post the Exception object to the Exception target of
' the batched join block.
selectEmployees.Target2.Post(e)
End Try
Next i
' Set the batched join block to the completed state and wait for
' all retrieval operations to complete.
selectEmployees.Complete()
printEmployees.Completion.Wait()
' Print the total error count.
Console.WriteLine("Finished. There were {0} total errors.", totalErrors)
End Sub
Metode ini mencetak informasi tentang karyawan acak ke konsol. Ini membuat beberapa objek acak Employee dan memanggil metode GetEmployeeID untuk mengambil pengidentifikasi unik untuk setiap objek. Karena metode GetEmployeeID ini memberikan pengecualian jika tidak ada karyawan yang cocok dengan nama depan dan belakang yang diberikan, metode GetRandomEmployees ini menggunakan kelas BatchedJoinBlock<T1,T2> untuk menyimpan objek Employee untuk panggilan ke objek GetEmployeeID dan System.Exception yang berhasil untuk panggilan yang gagal. Objek ActionBlock<TInput> dalam contoh ini bertindak pada objek Tuple<T1,T2> yang menyimpan daftar objek Employee dan daftar objek Exception. Objek BatchedJoinBlock<T1,T2> menyebarluaskan data ini saat jumlah jumlah objek Employee dan Exception yang diterima sama dengan ukuran batch.
Contoh Lengkap
Contoh berikut menunjukkan operasi kueri lengkap. Metode Main membandingkan waktu yang diperlukan untuk melakukan penyisipan database batch versus waktu untuk melakukan penyisipan database non-batch. Ini juga menunjukkan penggunaan gabungan buffered untuk membaca data karyawan dari database dan juga melaporkan kesalahan.
using System;
using System.Collections.Generic;
using System.Data.SqlServerCe;
using System.Diagnostics;
using System.IO;
using System.Threading.Tasks.Dataflow;
// Demonstrates how to use batched dataflow blocks to improve
// the performance of database operations.
namespace DataflowBatchDatabase
{
class Program
{
// The number of employees to add to the database.
// TODO: Change this value to experiment with different numbers of
// employees to insert into the database.
static readonly int insertCount = 256;
// The size of a single batch of employees to add to the database.
// TODO: Change this value to experiment with different batch sizes.
static readonly int insertBatchSize = 96;
// The source database file.
// TODO: Change this value if Northwind.sdf is at a different location
// on your computer.
static readonly string sourceDatabase =
@"C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Samples\Northwind.sdf";
// TODO: Change this value if you require a different temporary location.
static readonly string scratchDatabase =
@"C:\Temp\Northwind.sdf";
// Describes an employee. Each property maps to a
// column in the Employees table in the Northwind database.
// For brevity, the Employee class does not contain
// all columns from the Employees table.
class Employee
{
public int EmployeeID { get; set; }
public string LastName { get; set; }
public string FirstName { get; set; }
// A random number generator that helps tp generate
// Employee property values.
static Random rand = new Random(42);
// Possible random first names.
static readonly string[] firstNames = { "Tom", "Mike", "Ruth", "Bob", "John" };
// Possible random last names.
static readonly string[] lastNames = { "Jones", "Smith", "Johnson", "Walker" };
// Creates an Employee object that contains random
// property values.
public static Employee Random()
{
return new Employee
{
EmployeeID = -1,
LastName = lastNames[rand.Next() % lastNames.Length],
FirstName = firstNames[rand.Next() % firstNames.Length]
};
}
}
// Adds new employee records to the database.
static void InsertEmployees(Employee[] employees, string connectionString)
{
using (SqlCeConnection connection =
new SqlCeConnection(connectionString))
{
try
{
// Create the SQL command.
SqlCeCommand command = new SqlCeCommand(
"INSERT INTO Employees ([Last Name], [First Name])" +
"VALUES (@lastName, @firstName)",
connection);
connection.Open();
for (int i = 0; i < employees.Length; i++)
{
// Set parameters.
command.Parameters.Clear();
command.Parameters.Add("@lastName", employees[i].LastName);
command.Parameters.Add("@firstName", employees[i].FirstName);
// Execute the command.
command.ExecuteNonQuery();
}
}
finally
{
connection.Close();
}
}
}
// Retrieves the number of entries in the Employees table in
// the Northwind database.
static int GetEmployeeCount(string connectionString)
{
int result = 0;
using (SqlCeConnection sqlConnection =
new SqlCeConnection(connectionString))
{
SqlCeCommand sqlCommand = new SqlCeCommand(
"SELECT COUNT(*) FROM Employees", sqlConnection);
sqlConnection.Open();
try
{
result = (int)sqlCommand.ExecuteScalar();
}
finally
{
sqlConnection.Close();
}
}
return result;
}
// Retrieves the ID of the first employee that has the provided name.
static int GetEmployeeID(string lastName, string firstName,
string connectionString)
{
using (SqlCeConnection connection =
new SqlCeConnection(connectionString))
{
SqlCeCommand command = new SqlCeCommand(
string.Format(
"SELECT [Employee ID] FROM Employees " +
"WHERE [Last Name] = '{0}' AND [First Name] = '{1}'",
lastName, firstName),
connection);
connection.Open();
try
{
return (int)command.ExecuteScalar();
}
finally
{
connection.Close();
}
}
}
// Posts random Employee data to the provided target block.
static void PostRandomEmployees(ITargetBlock<Employee> target, int count)
{
Console.WriteLine("Adding {0} entries to Employee table...", count);
for (int i = 0; i < count; i++)
{
target.Post(Employee.Random());
}
}
// Adds random employee data to the database by using dataflow.
static void AddEmployees(string connectionString, int count)
{
// Create an ActionBlock<Employee> object that adds a single
// employee entry to the database.
var insertEmployee = new ActionBlock<Employee>(e =>
InsertEmployees(new Employee[] { e }, connectionString));
// Post several random Employee objects to the dataflow block.
PostRandomEmployees(insertEmployee, count);
// Set the dataflow block to the completed state and wait for
// all insert operations to complete.
insertEmployee.Complete();
insertEmployee.Completion.Wait();
}
// Adds random employee data to the database by using dataflow.
// This method is similar to AddEmployees except that it uses batching
// to add multiple employees to the database at a time.
static void AddEmployeesBatched(string connectionString, int batchSize,
int count)
{
// Create a BatchBlock<Employee> that holds several Employee objects and
// then propagates them out as an array.
var batchEmployees = new BatchBlock<Employee>(batchSize);
// Create an ActionBlock<Employee[]> object that adds multiple
// employee entries to the database.
var insertEmployees = new ActionBlock<Employee[]>(a =>
InsertEmployees(a, connectionString));
// Link the batch block to the action block.
batchEmployees.LinkTo(insertEmployees);
// When the batch block completes, set the action block also to complete.
batchEmployees.Completion.ContinueWith(delegate { insertEmployees.Complete(); });
// Post several random Employee objects to the batch block.
PostRandomEmployees(batchEmployees, count);
// Set the batch block to the completed state and wait for
// all insert operations to complete.
batchEmployees.Complete();
insertEmployees.Completion.Wait();
}
// Displays information about several random employees to the console.
static void GetRandomEmployees(string connectionString, int batchSize,
int count)
{
// Create a BatchedJoinBlock<Employee, Exception> object that holds
// both employee and exception data.
var selectEmployees = new BatchedJoinBlock<Employee, Exception>(batchSize);
// Holds the total number of exceptions that occurred.
int totalErrors = 0;
// Create an action block that prints employee and error information
// to the console.
var printEmployees =
new ActionBlock<Tuple<IList<Employee>, IList<Exception>>>(data =>
{
// Print information about the employees in this batch.
Console.WriteLine("Received a batch...");
foreach (Employee e in data.Item1)
{
Console.WriteLine("Last={0} First={1} ID={2}",
e.LastName, e.FirstName, e.EmployeeID);
}
// Print the error count for this batch.
Console.WriteLine("There were {0} errors in this batch...",
data.Item2.Count);
// Update total error count.
totalErrors += data.Item2.Count;
});
// Link the batched join block to the action block.
selectEmployees.LinkTo(printEmployees);
// When the batched join block completes, set the action block also to complete.
selectEmployees.Completion.ContinueWith(delegate { printEmployees.Complete(); });
// Try to retrieve the ID for several random employees.
Console.WriteLine("Selecting random entries from Employees table...");
for (int i = 0; i < count; i++)
{
try
{
// Create a random employee.
Employee e = Employee.Random();
// Try to retrieve the ID for the employee from the database.
e.EmployeeID = GetEmployeeID(e.LastName, e.FirstName, connectionString);
// Post the Employee object to the Employee target of
// the batched join block.
selectEmployees.Target1.Post(e);
}
catch (NullReferenceException e)
{
// GetEmployeeID throws NullReferenceException when there is
// no such employee with the given name. When this happens,
// post the Exception object to the Exception target of
// the batched join block.
selectEmployees.Target2.Post(e);
}
}
// Set the batched join block to the completed state and wait for
// all retrieval operations to complete.
selectEmployees.Complete();
printEmployees.Completion.Wait();
// Print the total error count.
Console.WriteLine("Finished. There were {0} total errors.", totalErrors);
}
static void Main(string[] args)
{
// Create a connection string for accessing the database.
// The connection string refers to the temporary database location.
string connectionString = string.Format(@"Data Source={0}",
scratchDatabase);
// Create a Stopwatch object to time database insert operations.
Stopwatch stopwatch = new Stopwatch();
// Start with a clean database file by copying the source database to
// the temporary location.
File.Copy(sourceDatabase, scratchDatabase, true);
// Demonstrate multiple insert operations without batching.
Console.WriteLine("Demonstrating non-batched database insert operations...");
Console.WriteLine("Original size of Employee table: {0}.",
GetEmployeeCount(connectionString));
stopwatch.Start();
AddEmployees(connectionString, insertCount);
stopwatch.Stop();
Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.",
GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds);
Console.WriteLine();
// Start again with a clean database file.
File.Copy(sourceDatabase, scratchDatabase, true);
// Demonstrate multiple insert operations, this time with batching.
Console.WriteLine("Demonstrating batched database insert operations...");
Console.WriteLine("Original size of Employee table: {0}.",
GetEmployeeCount(connectionString));
stopwatch.Restart();
AddEmployeesBatched(connectionString, insertBatchSize, insertCount);
stopwatch.Stop();
Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.",
GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds);
Console.WriteLine();
// Start again with a clean database file.
File.Copy(sourceDatabase, scratchDatabase, true);
// Demonstrate multiple retrieval operations with error reporting.
Console.WriteLine("Demonstrating batched join database select operations...");
// Add a small number of employees to the database.
AddEmployeesBatched(connectionString, insertBatchSize, 16);
// Query for random employees.
GetRandomEmployees(connectionString, insertBatchSize, 10);
}
}
}
/* Sample output:
Demonstrating non-batched database insert operations...
Original size of Employee table: 15.
Adding 256 entries to Employee table...
New size of Employee table: 271; elapsed insert time: 11035 ms.
Demonstrating batched database insert operations...
Original size of Employee table: 15.
Adding 256 entries to Employee table...
New size of Employee table: 271; elapsed insert time: 197 ms.
Demonstrating batched join database insert operations...
Adding 16 entries to Employee table...
Selecting items from Employee table...
Received a batch...
Last=Jones First=Tom ID=21
Last=Jones First=John ID=24
Last=Smith First=Tom ID=26
Last=Jones First=Tom ID=21
There were 4 errors in this batch...
Received a batch...
Last=Smith First=Tom ID=26
Last=Jones First=Mike ID=28
There were 0 errors in this batch...
Finished. There were 4 total errors.
*/
Imports System.Collections.Generic
Imports System.Data.SqlServerCe
Imports System.Diagnostics
Imports System.IO
Imports System.Threading.Tasks.Dataflow
' Demonstrates how to use batched dataflow blocks to improve
' the performance of database operations.
Namespace DataflowBatchDatabase
Friend Class Program
' The number of employees to add to the database.
' TODO: Change this value to experiment with different numbers of
' employees to insert into the database.
Private Shared ReadOnly insertCount As Integer = 256
' The size of a single batch of employees to add to the database.
' TODO: Change this value to experiment with different batch sizes.
Private Shared ReadOnly insertBatchSize As Integer = 96
' The source database file.
' TODO: Change this value if Northwind.sdf is at a different location
' on your computer.
Private Shared ReadOnly sourceDatabase As String = "C:\Program Files\Microsoft SQL Server Compact Edition\v3.5\Samples\Northwind.sdf"
' TODO: Change this value if you require a different temporary location.
Private Shared ReadOnly scratchDatabase As String = "C:\Temp\Northwind.sdf"
' Describes an employee. Each property maps to a
' column in the Employees table in the Northwind database.
' For brevity, the Employee class does not contain
' all columns from the Employees table.
Private Class Employee
Public Property EmployeeID() As Integer
Public Property LastName() As String
Public Property FirstName() As String
' A random number generator that helps tp generate
' Employee property values.
Private Shared rand As New Random(42)
' Possible random first names.
Private Shared ReadOnly firstNames() As String = {"Tom", "Mike", "Ruth", "Bob", "John"}
' Possible random last names.
Private Shared ReadOnly lastNames() As String = {"Jones", "Smith", "Johnson", "Walker"}
' Creates an Employee object that contains random
' property values.
Public Shared Function Random() As Employee
Return New Employee With {.EmployeeID = -1, .LastName = lastNames(rand.Next() Mod lastNames.Length), .FirstName = firstNames(rand.Next() Mod firstNames.Length)}
End Function
End Class
' Adds new employee records to the database.
Private Shared Sub InsertEmployees(ByVal employees() As Employee, ByVal connectionString As String)
Using connection As New SqlCeConnection(connectionString)
Try
' Create the SQL command.
Dim command As New SqlCeCommand("INSERT INTO Employees ([Last Name], [First Name])" & "VALUES (@lastName, @firstName)", connection)
connection.Open()
For i As Integer = 0 To employees.Length - 1
' Set parameters.
command.Parameters.Clear()
command.Parameters.Add("@lastName", employees(i).LastName)
command.Parameters.Add("@firstName", employees(i).FirstName)
' Execute the command.
command.ExecuteNonQuery()
Next i
Finally
connection.Close()
End Try
End Using
End Sub
' Retrieves the number of entries in the Employees table in
' the Northwind database.
Private Shared Function GetEmployeeCount(ByVal connectionString As String) As Integer
Dim result As Integer = 0
Using sqlConnection As New SqlCeConnection(connectionString)
Dim sqlCommand As New SqlCeCommand("SELECT COUNT(*) FROM Employees", sqlConnection)
sqlConnection.Open()
Try
result = CInt(Fix(sqlCommand.ExecuteScalar()))
Finally
sqlConnection.Close()
End Try
End Using
Return result
End Function
' Retrieves the ID of the first employee that has the provided name.
Private Shared Function GetEmployeeID(ByVal lastName As String, ByVal firstName As String, ByVal connectionString As String) As Integer
Using connection As New SqlCeConnection(connectionString)
Dim command As New SqlCeCommand(String.Format("SELECT [Employee ID] FROM Employees " & "WHERE [Last Name] = '{0}' AND [First Name] = '{1}'", lastName, firstName), connection)
connection.Open()
Try
Return CInt(Fix(command.ExecuteScalar()))
Finally
connection.Close()
End Try
End Using
End Function
' Posts random Employee data to the provided target block.
Private Shared Sub PostRandomEmployees(ByVal target As ITargetBlock(Of Employee), ByVal count As Integer)
Console.WriteLine("Adding {0} entries to Employee table...", count)
For i As Integer = 0 To count - 1
target.Post(Employee.Random())
Next i
End Sub
' Adds random employee data to the database by using dataflow.
Private Shared Sub AddEmployees(ByVal connectionString As String, ByVal count As Integer)
' Create an ActionBlock<Employee> object that adds a single
' employee entry to the database.
Dim insertEmployee = New ActionBlock(Of Employee)(Sub(e) InsertEmployees(New Employee() {e}, connectionString))
' Post several random Employee objects to the dataflow block.
PostRandomEmployees(insertEmployee, count)
' Set the dataflow block to the completed state and wait for
' all insert operations to complete.
insertEmployee.Complete()
insertEmployee.Completion.Wait()
End Sub
' Adds random employee data to the database by using dataflow.
' This method is similar to AddEmployees except that it uses batching
' to add multiple employees to the database at a time.
Private Shared Sub AddEmployeesBatched(ByVal connectionString As String, ByVal batchSize As Integer, ByVal count As Integer)
' Create a BatchBlock<Employee> that holds several Employee objects and
' then propagates them out as an array.
Dim batchEmployees = New BatchBlock(Of Employee)(batchSize)
' Create an ActionBlock<Employee[]> object that adds multiple
' employee entries to the database.
Dim insertEmployees = New ActionBlock(Of Employee())(Sub(a) Program.InsertEmployees(a, connectionString))
' Link the batch block to the action block.
batchEmployees.LinkTo(insertEmployees)
' When the batch block completes, set the action block also to complete.
batchEmployees.Completion.ContinueWith(Sub() insertEmployees.Complete())
' Post several random Employee objects to the batch block.
PostRandomEmployees(batchEmployees, count)
' Set the batch block to the completed state and wait for
' all insert operations to complete.
batchEmployees.Complete()
insertEmployees.Completion.Wait()
End Sub
' Displays information about several random employees to the console.
Private Shared Sub GetRandomEmployees(ByVal connectionString As String, ByVal batchSize As Integer, ByVal count As Integer)
' Create a BatchedJoinBlock<Employee, Exception> object that holds
' both employee and exception data.
Dim selectEmployees = New BatchedJoinBlock(Of Employee, Exception)(batchSize)
' Holds the total number of exceptions that occurred.
Dim totalErrors As Integer = 0
' Create an action block that prints employee and error information
' to the console.
Dim printEmployees = New ActionBlock(Of Tuple(Of IList(Of Employee), IList(Of Exception)))(Sub(data)
' Print information about the employees in this batch.
' Print the error count for this batch.
' Update total error count.
Console.WriteLine("Received a batch...")
For Each e As Employee In data.Item1
Console.WriteLine("Last={0} First={1} ID={2}", e.LastName, e.FirstName, e.EmployeeID)
Next e
Console.WriteLine("There were {0} errors in this batch...", data.Item2.Count)
totalErrors += data.Item2.Count
End Sub)
' Link the batched join block to the action block.
selectEmployees.LinkTo(printEmployees)
' When the batched join block completes, set the action block also to complete.
selectEmployees.Completion.ContinueWith(Sub() printEmployees.Complete())
' Try to retrieve the ID for several random employees.
Console.WriteLine("Selecting random entries from Employees table...")
For i As Integer = 0 To count - 1
Try
' Create a random employee.
Dim e As Employee = Employee.Random()
' Try to retrieve the ID for the employee from the database.
e.EmployeeID = GetEmployeeID(e.LastName, e.FirstName, connectionString)
' Post the Employee object to the Employee target of
' the batched join block.
selectEmployees.Target1.Post(e)
Catch e As NullReferenceException
' GetEmployeeID throws NullReferenceException when there is
' no such employee with the given name. When this happens,
' post the Exception object to the Exception target of
' the batched join block.
selectEmployees.Target2.Post(e)
End Try
Next i
' Set the batched join block to the completed state and wait for
' all retrieval operations to complete.
selectEmployees.Complete()
printEmployees.Completion.Wait()
' Print the total error count.
Console.WriteLine("Finished. There were {0} total errors.", totalErrors)
End Sub
Shared Sub Main(ByVal args() As String)
' Create a connection string for accessing the database.
' The connection string refers to the temporary database location.
Dim connectionString As String = String.Format("Data Source={0}", scratchDatabase)
' Create a Stopwatch object to time database insert operations.
Dim stopwatch As New Stopwatch()
' Start with a clean database file by copying the source database to
' the temporary location.
File.Copy(sourceDatabase, scratchDatabase, True)
' Demonstrate multiple insert operations without batching.
Console.WriteLine("Demonstrating non-batched database insert operations...")
Console.WriteLine("Original size of Employee table: {0}.", GetEmployeeCount(connectionString))
stopwatch.Start()
AddEmployees(connectionString, insertCount)
stopwatch.Stop()
Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.", GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds)
Console.WriteLine()
' Start again with a clean database file.
File.Copy(sourceDatabase, scratchDatabase, True)
' Demonstrate multiple insert operations, this time with batching.
Console.WriteLine("Demonstrating batched database insert operations...")
Console.WriteLine("Original size of Employee table: {0}.", GetEmployeeCount(connectionString))
stopwatch.Restart()
AddEmployeesBatched(connectionString, insertBatchSize, insertCount)
stopwatch.Stop()
Console.WriteLine("New size of Employee table: {0}; elapsed insert time: {1} ms.", GetEmployeeCount(connectionString), stopwatch.ElapsedMilliseconds)
Console.WriteLine()
' Start again with a clean database file.
File.Copy(sourceDatabase, scratchDatabase, True)
' Demonstrate multiple retrieval operations with error reporting.
Console.WriteLine("Demonstrating batched join database select operations...")
' Add a small number of employees to the database.
AddEmployeesBatched(connectionString, insertBatchSize, 16)
' Query for random employees.
GetRandomEmployees(connectionString, insertBatchSize, 10)
End Sub
End Class
End Namespace
' Sample output:
'Demonstrating non-batched database insert operations...
'Original size of Employee table: 15.
'Adding 256 entries to Employee table...
'New size of Employee table: 271; elapsed insert time: 11035 ms.
'
'Demonstrating batched database insert operations...
'Original size of Employee table: 15.
'Adding 256 entries to Employee table...
'New size of Employee table: 271; elapsed insert time: 197 ms.
'
'Demonstrating batched join database insert operations...
'Adding 16 entries to Employee table...
'Selecting items from Employee table...
'Received a batch...
'Last=Jones First=Tom ID=21
'Last=Jones First=John ID=24
'Last=Smith First=Tom ID=26
'Last=Jones First=Tom ID=21
'There were 4 errors in this batch...
'Received a batch...
'Last=Smith First=Tom ID=26
'Last=Jones First=Mike ID=28
'There were 0 errors in this batch...
'Finished. There were 4 total errors.
'
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