Once concurrency on a database reaches a certain level the chances of deadlocks increase. Whenever a deadlock occurs there will be at least one transaction that is a victim.

Deadlocks also have a negative effect on performance.

What about protection of data

Without going into detail (see further reading below) READ_COMMITTED_SNAPSHOT provides the same level of protection against dirty reads as the current SQLServer default (READ_COMMITTED).

The payload of SNAPSHOT is increased resource usage. However compared to the resources lost from creation of LOCKS this doesnt seem to be a big issue.

I have deadlocks and SQLServer 2000, what do I do?

In this situation you are a little snookered!
The only strategy is to determine which queries are being locked/being selected as dead lock victims and reduce the lock protection on them by adding WITH(NOLOCK) to the table selection.
e.g.

SELECT * FROM Articles WITH(NOLOCK)

Example a Deadlock error message

Transaction (Process ID 98) was deadlocked on lock resources with another process and has been chosen as the deadlock victim. Rerun the transaction.

How to enable it

To enable READ_COMMITTED_SNAPSHOT you must have the only active connection to the database you want to enable it on.

1. Log everyone off the database server
2. Restart the MSSQL service.
3. Open Developer Studio – you now have the only active connection to the database
4. Run: “ALTER DATABASE MyDatabase SET ALLOW_SNAPSHOT_ISOLATION ON”
5. Run: “ALTER DATABASE MyDatabase SET READ_COMMITTED_SNAPSHOT ON”
6. Complete

Note: If either of the queries in points 4 or 5 take a long time to complete (more than a few seconds) it is likely you do not have the only active connection. Check in the activity monitor for information on active sessions.

Things to be aware of

When enabled ALLOW_SNAPSHOT_ISOLATION keeps an archive of all changed values in the tempdb (it will automatically clear these up after it is finished with them). You should check the location of the tempdb and ensure there is available space on that drive.

Further Reading

http://msdn.microsoft.com/en-us/library/tcbchxcb(VS.80).aspx

One problem, it didnt work! This was a big suprise to me, as I expected it to work “out the box”. Two days, 3 hours fiddling with suggestions and settings I happened on the post below:

http://www.internettablettalk.com/forums/showthread.php?p=48550#post48550

The linked post sorted out all my problems!

I tried renaming the jre directory in the Aptana Program Files folder as suggested in the Aptana FAQ, but no joy. So I did a little digging and found this : http://forums.aptana.com/viewtopic.php?p=22803&sid=c2bd9586a773ff9be69c4b6e84d33d12

This lead me to deleting the tigris folder from plugins/ .. Hey presto, aptana now boots again. As a clean up step I disabled the Subelipse plugin altogether once I could get the plugin manager back up.

Many hours of searching MSDN and Google later I was a little the wiser (not much) about how to deal with proxy’s and authentication with .NET (I’m using v2 of the framework)

The first thing to check is whether .NET will auto detect the fact there is a proxy (from IE) or whether we have to set this manually. This depends on the <defaultProxy> element in the .config file. Check out this page for info: http://msdn2.microsoft.com/en-us/library/sa91de1e(VS.80).aspx Particularly the following note:

“The proxy element defines a proxy server for an application. If this element is missing from the configuration file, then the .NET Framework will use the proxy settings in Internet Explorer.”

So – what we could assume from this is that if the setting is not there – all should work fine and dandy… well this would be true up to a point – and that point is authentication.

Authentication

Does the Proxy server authenticate using the default credentials of the user logged into windows? If so then we either want:

a) useDefaultCredentials=”true” in the default proxy config element, also see: http://geekswithblogs.net/mnf/archive/2006/03/08/71663.aspx

b) or we want to “WebRequest.DefaultWebProxy.Credentials = CredentialCache.DefaultCredentials;”

Credentials arnt stored in the Default Credentials? This is the situation you are in if have a user/pass box popup when you first navigate to a page in IE.

  NetworkCredential nc = new NetworkCredential("ProxyUser","ProxyPassword", "ProxyDomain");

  WebRequest.DefaultWebProxy.Credentials = nc;

Other interesting reading about a specific problem that you might be having:

http://geekswithblogs.net/mnf/archive/2006/09/13/91012.aspx

http://www.dotnet247.com/247reference/msgs/52/263150.aspx