Sticky Transaction Isolation Level in Pooled Connections

omg!  Why are we getting so many deadlocks on the web site?!

When you change the isolation level on a pooled connection, it stays changed.  If you want to run a few things in a higher isolation level and you set the level to Serializable on a TransactionScope, finish your work, and complete the TransactionScope, the connection is returned to the pool with the current isolation level.  It does not revert to its default isolation level.

Our friends at Microsoft say this is by design: Article ID: 972915.

If you set it up, set it back down before releasing the connection.


Recently we had a bizarre response from a server when attempting to access a web site.

If I browse to, the web site redirects to

Turns out the (X(1)) is ASP.NET attempting to run in cookieless mode. The cuprit is the combination of the underscore in the URL and having your web configured to autodetect cookies:

    <authentication mode="Forms">
      <forms cookieless="AutoDetect" />

Here’s the sequence of events:

I send a request for

The server responds with a 302 redirect to and will include a AspxAutoDetectCookieSupport=1 cookie.

Normally, your browser would respond with a request to the new URL with the added querystring, as well as the cookie, and the system would continue on, but with the underscore in the URL, your browser (up to and including IE10) doesn’t consider this to be a valid domain, so it doesn’t send the cookie back.

ASP.NET then goes into cookieless mode, according to this MSDN article: Understand How the ASP.NET Cookieless Feature Works.

The solution is to remove the underscore from your URL, or (if your application requires cookies) to change your cookieless setting to “UseCookies”.

MSDN article describing why IE doesn’t play nicely with underscores in a URL: Article ID: 241980.