Azure SQL DB Managed Instances: Trace Flags, Ahoy!

When you talk to people from Microsoft

They’re all “aw shucks” about Trace Flags.

  • “Don’t really need’em!”
  • “Eh, haven’t used one in years.”
  • “Sometimes they’re good for troubleshooting, but…”

Then you hop on a managed instance (where you’re not allowed to turn Trace Flags on or off), and you see what they have turned on.

28 trace flags… in a row?

If you head over to Konstantin Taranov’s GitHub repo for Trace Flags, you can decode some of them.

Missing from the list:

  • 2591
  • 3447 (but 3448 is there, which is supposed to help fix an issue with hung Mirrored databases)
  • 3978
  • 4141
  • 5521
  • 7838
  • 8037
  • 8054
  • 8057
  • 8063
  • 8065
  • 9041
  • 9537
  • 9570
  • 9883
  • 9905
  • 9934
  • 9940
  • 9941

See where I’m going with this? Konstantin has a GREAT LIST but there are still 19 unknowns enabled on every Managed Instance.

Kinda makes you wonder what all these Trace Flags are up to behind the Redmond Curtain.

If you know what any of them do, feel free to leave a comment — or better yet, add an Issue for Konstantin so he can keep his list up to date.

Some of them are startup Trace Flags, so if you’re aiming to do some poking around, it may not help you to just flip them on.

-xcopy is the name of my xtc tribute band

Thanks for reading!

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5 Comments. Leave new

  • i’m not familiar with any of those yet… but i’m really surprised that 4199 isn’t in the list of enabled trace flags. Even though the database scoped config option QUERY_OPTIMIZER_HOTFIXES *should* be equivalent… cases of it being late and having to catch up keep being discovered.

    • Erik Darling
      March 16, 2018 7:17 am

      I’m not either, but perhaps they’d be helpful to people suffering from VM Problems®


  • Andrew Notarian
    May 13, 2023 8:02 pm

    I can’t believe it took me 5 years to notice this XTC reference. Trace Flags on MI still haunt us all.


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