Ah!  When you shoot yourself in the foot... a few times... it hurts!

That's what I did on Sunday, to learn more about the behavior of the SQL Azure Denial Of Service prevention feature. This article is a short follow up to my last post on this feature. In this post, I will outline some of the lessons learned that were the result of testing the behavior of SQL Azure from two machines. From the standpoint of SQL Azure, they look like one machine since they are behind a NAT.

• All logins affected
  The first thing to note is that all the logins are affected. If you lock yourself out to a specific database, none of the logins will work on that database. In fact the database size becomes "--" in the SQL Azure Portal.
   
• Less than 100 sessions
  I was able to see 50+ sessions being made in SQL Azure (by looking at sys.dm_exec_sessions) before being locked out. The the DoS feature appears to be triggered in part by the number of open sessions. I could not determine if the lockout is triggered by the speed at which connection requests are made however.
   
• Other Databases Unaffected
  This was interesting... the DoS feature works at the database level. Other databases were available for me to use.
   
• Just Wait
  Initially I thought that going through SQL Azure and connecting from there would reset the database and allow me to connect again. Unfortunately this doesn't seem to be the case. You will have to wait. And the more you lock yourself out, the more you will have to wait... The first time the database became available again within 30 seconds or so; the second time within 2-3 minutes and the third time... within 2-3 hours...
   
• Successful Logins
  The DoS feature appears to engage only for valid logins. If you have a login failure, it doesn't seem to count. I ran a test with over 100 login failures without being locked.