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DBA 101 - Connecting to an unresponsive SQL Server

I will attempt, over the course of many blogs, to tackle troubleshooting for a beginning to intermediate DBA. Troubleshooting is like an octopus with a hundred arms. There is no silver bullet but at least I can give you some tools for your belt to help determine the next steps in troubleshooting many common problems that you will see. So where do we begin? I don't know. Let's dive in and see where we end up.
Problem - Nobody can connect to the SQL Server and it is not responding to any requests. Wow this seems like an impossible problem and is in reality two problems. Lets address the most critical problem which is you cannot even address why the SQL Server isn't responding to requests because nobody can connect to it to see what is going on.
A weak solution - Often times an inexperienced DBA or what is often called an "accidental" DBA would pull the plug on the server, wait ten seconds, and then power it back on. Now this isn't the worst possible solution...because it will likely work. The real problem with doing this is you never find out what caused the problem which means you are likely to relive this problem in the future. This will get old fast and stress you out waiting for the occurrence with no permanent solution.

A better solution - What you really need to do is connect to this SQL Server. I know the base problem states nobody can connect but you are a better DBA now. You look up blogs and posts on how to connect to an unresponsive SQL Server. So here it is. SQL 2005 introduced a new tool for administrators to connect to an unresponsive SQL Server called DAC - Dedicated Administrator Connection. SQL Server reserves memory for just this connection. You must be on the server to use this connection, no network connections allowed. Read how to connect to SQL Server using the DAC here. Once you have connected you can troubleshoot normally.
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Comments

  1. SYOUNGSeptember 6, 2010 at 9:06 PM

    Tony,

    I have an observation about your post. If the server configuration "remote admin connections" is not enabled, the DAC will not work. I get the error "Dedicated administrator connections are not supported". Once I enable the remote admin connections on the server, I'm able to connect using the DAC as described by BOL.

    ReplyDelete
  2. Tony VolnerSeptember 28, 2010 at 3:49 PM

    and you know even the link to MSDN I provided to cover all the details doesn't even mention that. Good catch and thanks!

    ReplyDelete

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