5pm Posts

.Net 1 / 1.1

APM (Asynchronous Programming Model)

Begin/End method pairs

Begin

Difficult to perform async composition, eg: wait for 2 async operation before performing next step

returns IAsyncResult (token)

takes a delegate (called by the operation when the async operation is finished)

delegate callback calls End when done passing in the token

End

returns void/object

Example 

public static void Main() { FileStream fs = new FileStream(...); // Begin an asynchronous read operation IAsyncResult token = fs.BeginRead(...); // Suspend this thread until the asynchronous operation completes and get the result var bytesRead = fs.EndRead(token); fs.Close(); }

Example

public static void Main() { FileStream fs = new FileStream(...); // Begin an asynchronous read operation // Pass callback delegate and fs as parameter to delegate fs.BeginRead(..., ReadComplete, fs); } private static void ReadComplete(IAsyncResult token) { // Extract the FileStream (state) out of the IAsyncResult object FileStream fs = (FileStream) token.AsyncState; // Get the result Int32 bytesRead = fs.EndRead(token); fs.Close(); }

.Net 2

EAP (Event-based Asynchronous Pattern)

FooAsync and FooCompletedEvent pair

Caller first subscribes to the event, then calls the async method

Hides IAsyncResult, rather than you passing delegate, you attach the callback to the event

Utilizates synchronization context, marshalls data between threads for you

eg: BackgroundWorker

Example:

public static void Main() { WebClient client = new WebClient(); // Specify that the DownloadStringCallback method gets called when the download completes. client.DownloadStringCompleted += new DownloadStringCompletedEventHandler (DownloadStringCallback); client.DownloadStringAsync(...); } private static void DownloadStringCallback (Object sender, DownloadStringCompletedEventArgs e) { if (e.Cancelled || e.Error == null) return; Console.WriteLine((string)e.Result); }

.Net 4

TAP (Task Asynchronous Pattern)

returns Task (promise), includes methods for status and helps with composition

async/await keywords

converts methods to state machine, more functional

compilers split method into 2

1st part is before call to task returning method

2nd part is after call to task returning method

2nd part is passed as a callback to the Task

Example:

public static void Main() { using (FileStream fs = new FileStream(...)) { result = new byte[fs.Length]; await fs.ReadAsync(result, 0, (int)fs.Length); } }

References

Locations of the various logs on the website’s local file system

Event Log

Useful for capturing unhandled exceptions that may have escaped the application’s exception handling logic and surfaced to the web server

Single XML file per website

Located at \LogFiles\eventlog.xml

Web server logs

Stores a line for each HTTP request to the website

Multiple Text files 

Located at \LogFiles\http\RawLogs\*.log

Detailed error message logs

Logs the error messages for failed requests that result in an HTTP status code of 400 or higher

Multiple HTML files, one error message per file

Located at \LogFiles\DetailedErrors\ErrorPage######.htm

Failed request tracing logs

Logs the stack trace that led to a failed HTTP request

Multiple XML documents, one error per file (includes a *.xsd file for viewing in browsers)

Located at \LogFiles\W3SVC*\*.xml 

Application diagnostic logs

Created by application code using System.Diagnostics.Trace class in C# 

Multiple Text files

Located at \LogFiles\Application\*.txt

For example:

You can view these using:

Visual Studio

“Azure website logs browser” management portal extension

Kudu portal https://<yoursite>.scm.azurewebsites.net/DebugConsole

FTP client  

Here are some of the popular distributed caching products...

Memcached

Windows Server AppFabric Cache (formerly Velocity)

Here are some of the principles to keep in mind while creating your caching layer...

Dead Servers

Attempts to reconnect to a dead server introduces Network dealys and must be minimized. Memcached supports the following...

auto eject hosts

retry timeout

redundancy

Key Hashing

modulo hashing - removal of a server causes majority of cache keys to be remapped

consistent hashing - better approach - removal of a server remaps K/n cache keys [http://sourceforge.net/apps/mediawiki/kai/index.php?title=Introduction]

Thundering Herd (stampede) problem

invalidating a heavily accessed cache key results in several clients requesting cache to refetch from the data store resulting in delays

in the client, consider doing the following to improve performance

use the invalidated value

refetch from the data store before deleting from cache

use a single client to refetch data

Maximum object size constraint

Excellent article and cheatsheet on SQL joins:

Here are examples of the EF Fluent API usage:

Here's an excerpt from an excellent article by Robert Rees @ ThoughtWorks...

Being a developer, we often write code related blog posts and often struggle with its' formatting. Here's what I need:

Render code with good formatting

Allow copy and paste

Allow me to manage changes to the code

It's been around for a while now, but Gist deserves to be the source view provider on all blogs. This post details how to get that to work on Tumblr in less than 5 minutes. 

Here's a working demo.

I was on a mid size business site recently and happened to discover how they did their vertical navigation menu ribbon. This is no rocket science, but was surprised that they had built a space ship by embedding image tags and additional spans, stuff that should be pure CSS concern, to their DOM.

SQL Server supports importing data from text files. This is a really performant way to insert large data sets in a single operation. The following example imports it from a CSV file:

bulk insert test from 'C:\data.csv' with ( fieldterminator=',', rowterminator='\n' )

Lets say you want to archive data (from @table1) between a date range to an archive table (@table2). SQL Server 2008 and beyond support the following:

delete from @table1  output deleted.* into @table2  where CreatedOn >= @dateDay1 and CreatedOn < @dateDay2

From EF 4.2 Code First Walkthrough:

The full list of annotations supported in EF is;

KeyAttribute

StringLengthAttribute

MaxLengthAttribute

ConcurrencyCheckAttribute

RequiredAttribute

TimestampAttribute

ComplexTypeAttribute

ColumnAttribute  Placed on a property to specify the column name, ordinal & data type

TableAttribute  Placed on a class to specify the table name and schema

InversePropertyAttribute  Placed on a navigation property to specify the property that represents the other end of a relationship

ForeignKeyAttribute  Placed on a navigation property to specify the property that represents the foreign key of the relationship

DatabaseGeneratedAttribute  Placed on a property to specify how the database generates a value for the property (Identity, Computed or None)

Important caveat while deciding on DDD, from Microsoft® Application Architecture Guide, 2nd Edition (Patterns & Practices)