Connect-DbaInstance - Set NonPooledConnection on ServerConnection for…

[mbentham]

Type of Change

• Bug fix (non-breaking change, fixes Connect-DbaInstance - DedicatedAdminConnection causes SQL Server error 17810 due to missing NonPooledConnection on ServerConnection #10259, Sync-DbaAvailabilityGroup DAC Connection Issue; sync login permissions #10256 )
• New feature (non-breaking change, adds functionality, fixes # )
• Breaking change (affects multiple commands or functionality, fixes # )
• Ran manual Pester test and has passed (Invoke-ManualPester)
• Adding code coverage to existing functionality
• Pester test is included
• If new file reference added for test, has is been added to github.com/dataplat/appveyor-lab ?
• Unit test is included
• Documentation
• Build system

Purpose

Fix SQL Server error 17810 ("maximum number of dedicated administrator connections already exists") when using Connect-DbaInstance -DedicatedAdminConnection. The DAC connection is not kept open between SMO operations because ServerConnection.NonPooledConnection is never set in the String input path, causing rapid connect/disconnect cycling that races against SQL Server's DAC slot release.

Approach

Added $server.ConnectionContext.NonPooledConnection = $true in the String input path of Connect-DbaInstance, alongside the existing ConnectionContext property assignments (BatchSeparator, LockTimeout, etc.). This is gated on $NonPooledConnection which covers both -DedicatedAdminConnection and explicit -NonPooledConnection usage.

The same pattern already exists in the Server/copy-context path (line ~711) and in New-DbaConnectionString (line ~465) — this change brings the String input path in line with both.

Commands to test

# Clear the error log first so results are unambiguous
Invoke-DbaQuery -SqlInstance localhost -Query "EXEC sp_cycle_errorlog"

# Connect via DAC, run a query, disconnect
$server = Connect-DbaInstance -SqlInstance localhost -DedicatedAdminConnection
Invoke-DbaQuery -SqlInstance $server -Query "SELECT @@servername"
$server | Disconnect-DbaInstance

# Check SQL Server error log for 17810 - should return no rows
Invoke-DbaQuery -SqlInstance localhost -Query "EXEC xp_readerrorlog 0, 1, N'17810'"

Before fix: xp_readerrorlog returns rows showing error 17810 logged during the DAC session (sometimes, depending on how quickly your particular SQL Server cleaned up the closing DAC connection - its an intermittant race condition).
After fix: No 17810 entries — the DAC connection stays open for the duration instead of cycling.

Learning

• SqlConnectionInfo.Pooled and ServerConnection.NonPooledConnection are independent settings. Pooled = $false controls SqlClient connection pooling (Pooling=false in the connection string), while NonPooledConnection = $true controls whether SMO auto-disconnects after each operation. Both are required for DAC connections to work correctly.

[andreasjordan]

I can run your "commands to test" even without your fix. So I don't see the problem.

[mbentham]

Yeah sorry I should have been clearer its a tricky one - the DBAtools commands run fine with no errors in powershell without the fix, but theres a race condition caused by cycling the connection that causes the SQL Server instance to log error 17810 "maximum number of dedicated administrator connections already exists" to the SQL Server log file if the the DAC connection isnt cleaned up quickly enough by SQL Server before the next DBATools command is sent, often the DBAtools command still succeeds anyway due to the automatic retry in SqlClient that SMO, and therefore the Connect-DbaInstance tool inherits. But if anyone is checking the sql server error logs, or has a monitoring tool that flags server errors they'll see the errors caused by this module.

I've improved the commands to test section

[andreasjordan]

Ok, so I need to create a loop and open/close the connection multiple times to see the problem?

But I still see no change, as $server.ConnectionContext.NonPooledConnection = $true has no effect as $server.ConnectionContext.NonPooledConnection is already $true without the change. Or am I missing something?

[andreasjordan]

Ok, with a loop, I can reproduce the issue:

foreach ($i in 1..1000) {
    $dac = Connect-DbaInstance -SqlInstance fci01 -DedicatedAdminConnection
    $null = Invoke-DbaQuery -SqlInstance $dac -Query "SELECT @@servername"
    $null = $dac | Disconnect-DbaInstance
}

And with your fix, the issue really seems to be resolved.

[andreasjordan]

Tested it - it works! Thanks for your contribution.

[mbentham]

Brilliant thanks, I'll be sure to be clearer in the PR next time, save the confusion.

[potatoqualitee]

Thank you so much! 🔥 🚒