User Answers

Short answer: yes, you can certainly do this if you want to and the result is valid.  The main downside, in my opinion, is that the backup is then dependent on more technology, so there are more things that could go wrong.  More on that later

If you log the error with ^%ETN (as in DO BACK^%ETN, or LOG^%ETN, or exceptionobject.Log()), the SETs to the ^ERRORS global are done with the transaction "suspended", so that it does not roll back.  In the future, we will be exposing this functionality for use in applications.  These get recorded in the journal so that they are recovered upon a system crash or restored in a journal restore, but they are omitted from rollback.  As others have said, ^%NOJRN is not the answer because it is ignored for mirrored databases.

I hesitate to comment on this because you know the answer, but it seems that if you're trying determine if a value is a number in canonical form, it's hard to beat testing that (x=+x).  

I don't think we should be so excited about the suggestion for sorts after $c(0), because that introduces dependencies on the the current local collation strategy.  Whatever answer you choose, I think you should require it to be invariant 

 

This behavior looks correct to me (but it's tricky).  The reason is that the string "2.2" is a number in canonical form, so it collates with the numeric subscripts. "1.0" is non-cananonical, so it's stored as a string subscript.  Sorts after operation is all about resolving subscript ordering.  You can convince yourself of this behavior by actually setting these as subscripts in a global or local variable and then ZWRITE'ing it

Upon return from ExternalFreeze(), the CACHE.DAT files will contain all of the updates that occurred prior to when it was invoked.  Some of those updates may, in fact, be journaled in the file that was switched to (the .003 file in your example), though that doesn't really matter for your question

%Library.Device class has GetMnemonicDirectory() and GetMnemonicRoutine()

This is the latest maintenance release and I know of no bug like this there, so this needs to be investigated to understand the error.  To your original question, there is nothing special you need to do to run SQL SELECT against an async mirror member, even when its databases are read-only.

There were problems like this in query compilation in some versions?  What error do you get and what version are you using?

The biggest thing you want to do is use three-argument $order to collapse from two global references to one:  $ORDER(^[Nspace]LAB(PIDX),1,Data)

In regards to the question about setting BBData or other small variants like that, it may very much be data-dependent and depend on what happens later in the loop that you haven't showed us.  But generally speaking if you're going to calculate the $p more than once, you probably do want to store it in a (private) variable