Question

i Dispose an SqlConnection object, but of of course it isn’t really closed. i need closed connection to not hold locks on database objects. How can i prevent closed connections from holding locks?

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Explanation of the above sentance for those who don’t know:

• When you close an ADO or ADO.NET connection, you aren’t actually severing the connection to SQL Server. The ADO/ADO.NET infrastructure keeps the connection around in case you want to use it again. The connections are kept lingering around in what’s called “The Connection Pool”.

• After a few minutes of not being used, the connection will be actually closed. Although, not really. TCP/IP has it’s own method for keeping TCP connections open for a few more minutes (in the “CLOSE_WAIT” state). This is done in case you ask to open a TCP connection to the same IP:Port again. If so, it can use that already open TCP connection.

• With connection pooling and SQL Server, the connection is still established to SQL Server. Each connection has a database context that it is sitting in. As long as a connection is sitting in that database: it holds a shared database (S-DB) lock on that database.

• A Shared-Database lock simply means, “Don’t delete this database while i’m in it please.”

How can i prevent it from holding a shared lock on my database, while keeping the benefits of connection pooling?

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My ad-hoc solution right now is every time a developer called Dispose:

connection.Dispose()

change it into a call to a global helper function:

Database.DisposeConnection(connection);

which changes the database context to master:

public static void DisposeConnection(SqlConnection connection)
{
    //Stop holding a database lock - in my database at least
    ADOHelper.ExecuteNonQuery(connection, "USE master");

    connection.Dispose();
}

It solves my immediate problem; closed connections aren’t holding a lock on my database.

But now i’m worried that connection pooling will have its brain scrambled – because i switched database contexts behind its back.

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In case anyone didn’t know, or thought otherwise:

From the SDK:

Close and Dispose are functionally
equivalent.

Answer 1

You can place the database in single user mode in order to restore it. IIRC, something like this…

ALTER DATABASE TheDatabaseToRestore SET SINGLE_USER WITH  ROLLBACK IMMEDIATE;
RESTORE DATABASE TheDatabaseToRestore 
FROM DISK =N'Z:\Path\To\Backup\BackupFile';
ALTER DATABASE TheDatabaseToRestore SET MULTI_USER;

see: Obtain Exclusive Access to Restore SQL Server and/or Restore Database Backup using SQL for some more background.

Edit: Single user mode is intended for backups and restores (which, on the non-express edition, is what I use it for regularly). Using it kicks out all other connections, and new connections cannot be made. I haven’t played with the various “WITH” options such as with “ROLLBACK IMMEDIATE”, but their usage seems straightforward.