Sushil's WebLog : Notification Support

SqlDependency changes for RTM

sushilc — Tue, 27 Sep 2005 19:49:00 GMT

I just posted a blog on our team webpage on the changes in new SqlDependency feature from Beta 2 to RTM. There have been a lot of changes since we shipped in Beta 2. Do let us know what you think of the new changes. We are looking forward to hear about this.

Getting Notifications to Work.

sushilc — Mon, 31 Jan 2005 17:44:00 GMT

With good things said about Notification in my previous blog, I will like to take a step further to walk you through some common issues in setting up this feature. We would need to undestand how notifications internally work to track some of these issues. Lets start with the SqlDependency object. When we create a SqlDependency object we are creating a listener on the client to track notifications sent by the server. There are two types of protocol options that SqlDependency supports – HTTP and TCP when creating a listener. The HTTP listener uses the HTTP.SYS functionality to create a listener. By default when no protocol option is specified, we try to create an HttpListener; if that for some reason fails, we create a TCPListener. When a change occurs, the server then dispatches notification messages via a .Net Procedure to the client listener. Now, let’s go over some common issues.

My Application doesn’t get Notification messages at all:

There could be many reasons why we could end up with this. Here are some reasons.

Is CLR enabled on SQL Server?

Cause: Since the code on the SQL server that dispatches notification messaged to the client is a .Net Procedure, you will have to enable CLR on Server. We are working on not requiring this restriction.:)

Solution: Here is way to do this for now,

EXEC sp_configure 'show advanced options', '1'
go
RECONFIGURE
go
EXEC sp_configure 'clr enabled', 1
go
RECONFIGURE

Does the SQL user have permissions on the Queue and/or the Service

Cause: Since this feature uses the SQL Server Service Broker (aka SSB) infrastructure to get notification, the user has to have the permissions on the Notification Service.

Solution: To grant the permission to user ‘Willy’ on the Service and queue use:

GRANT SEND on service::SqlQueryNotificationService to Willy

GRAND RECEIVE on SqlQueryNotificationService_DefaultQueue to Willy

Also the user needs permission to subscribe to notification. To do this use:

GRANT SUBSCRIBE QUERY NOTIFICATIONS TO Willy

Is it an XPSP2 machine and/or you using a firewall to block ports?

Cause: As said above, Notifications are dispatched from the server to the client via listener that sits on the client. With XPSP2 we have firewall enabled by default. Since the firewall will block any message sent to your TCP/HTTP ports, this may not generate Notification event.

Solution: Make sure these are open for the application.

I get an instantaneous notification telling that the Subscription failed.

Cause: There are set of requirements that are placed on the queries for which are notifiable . Basically, the restrictions are quite similar to restrictions for Indexed Views in SQL Server 2000. More information on these requirements can be found at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/createdb/cm_8_des_06_9jnb.asp

Solution: Queries that pass the above requirements can only be used.

Disclaimer: This posting is provided "AS IS" with no warranties, and confers no rights

Notification Support in SqlClient Managed Provider

sushilc — Tue, 07 Dec 2004 17:47:00 GMT

After a brief hiatus, let me start with blogging the new Notification support in SqlClient MP that is introduced in Whidbey. There are scenarios in which an application would store a cache of data obtain from a DB Server and then re-query from the same cache to save round-trips to the server (for better performance). Typically, the app would want some mechanism to be notified when this very cache was changed by some one. In short, this feature allows you to monitor a specified result-set (collection on table rows, as defined by your select statement.) and then notify you when something is changed in the monitored result-set.

In this blog, I will just post a sample illustrating on how easy it is to set a result-set for Notification. In the upcoming blogs, I will get into more details with some gotchas, tips and tricks with Notifications. Lets see how simple its to get this working. Lets say way, create a table test with following TSQL

create table test (i int)
go
insert into test values (1)
insert into test values (2)
insert into test values (3)
insert into test values (4)
go

The following sample shows how a console application that reads data from the 'test' table into its cache and will get notified if some one has made changes to this cache on the server.

using System;

using System.Data;

using System.Data.SqlClient;

class QuikExe

{

string connectionstring = "Put you connection string here";

public void DoDependency()

{

using (SqlConnection conn = new SqlConnection (connectionstring))

{

conn.Open();

Console.WriteLine("Connection Opened...");

SqlCommand cmd = conn.CreateCommand();

cmd.CommandText = "Select i from dbo.test";

//Notification specific code

SqlDependency dep = new SqlDependency (cmd);

dep.OnChanged += new OnChangedEventHandler(TestEvent);

SqlDataReader r = cmd.ExecuteReader();

//Read the data here and close the reader

r.Close();

Console.WriteLine("DataReader Read...");

}

void TestEvent(Object o,SqlNotificationEventArgs args)

{

Console.WriteLine("Event Recd");

Console.WriteLine("Info:" + args.Info );

Console.WriteLine("Source:"+args.Source );

Console.WriteLine("Type:"+args.Type );

}

public static void Main()

{

QuikExe q = new QuikExe();

q.DoDependency();

Console.WriteLine("Wait for Notification Event...");

Console.Read();

}

Run the above application and you will see the following output
Connection Opened...
DataReader Read...
Wait for Notification Event...

To verify that we indeed get a notification when the test table is change. Now invalidate the cache that we read using the following T-SQL statement (using any client tools-Workbench or another console Application :))
insert into test values (5)

Now, you will see the following Notification message from the above application
Event Recd
Info:Insert
Source:Data
Type:Change

Great! All we did here was to create a SqlDependency object and associate the Command to it before executing.
SqlDependency dep = new SqlDependency (cmd);

Also, to get notified we added a call-back event.
dep.OnChange += new OnChangeEventHandler(TestEvent);

The SqlNotificationEventArgs in turn has three properties which are enums:
1. Info - Gives information on what caused the notification.
2. Source - Gives the source of this notification.
3. Type - Type of notification.
Since in our case an Insert statement caused a Change in Data. The args properties are set as Info=Insert;Source=Data;Type=Change;

Note: Since the supporting functionality that makes this happen (SSB) is only available in SQL Server 2005 (Yukon), the above code will only work with SQL Server 2005.

So how did all this happen? In SQL Server 2005, we have a SSB service running in the MSDB database (called the SqlQueryNotificationService). When a command associated with a SqlDependency executes; it makes a request to this service for being notified if there occurred any change in the obtained result set. When a change occurs, the SSB service then puts a notification message in a specified Queue. The server then send the message from the queue to the client. The client then calls the call-back Event appropriately.

Tips and tricks to be aware while using SqlDependency is coming soon,
Stay posted.