Or add 

n $namespace

before the call. Once you go up in the stack the namespace will be switched to your current namespace automatically.

It would not unless you exit the current stack level. To achieve it, you should perform the one-liner as an argument of Xecute command, making it less pleasant, e.g. 

x "new $namespace set $namespace=""%SYS"",P(""Globals"")=""%DEFAULTDB"",sc=##class(Config.Namespaces).Create(""%All"",.P)"

I've succeeded with the code: 

%SYS>s P("Globals")="%DEFAULTDB"
%SYS>s P("Library")="IRISLIB"
%SYS>s P("Routines")="%DEFAULTDB"
%SYS>s P("SysGlobals")="IRISSYS"
%SYS>s P("SysRoutines")="IRISSYS"
%SYS>s P("TempGlobals")="IRISTEMP"
%SYS>Set tSC=##class(Config.Namespaces).Create("%All",.P) zw tSC
tSC=1
%SYS>w $zv
IRIS for UNIX (Ubuntu Server LTS for x86-64) 2021.1 (Build 215) Wed Jun 9 2021 09:48:30 EDT

...make sure all integrations should work fine

Hi,

That's very important note.

As to our experience of moving to IRIS our company's main development server, the most of the problems occurred outside IRIS: a "forgotten" Gitlab runner, or Ansible script, or other integration stuff. Those problems were mostly faced after the new server had been "lifted and shifted", as the correspondent pieces of software were the parts of our development cycle and could run on working environment only.

In contrast, we had virtually no problems inside IRIS as our COS code had been preliminary converted and partially rewritten to achieve IRIS compatibility; the developers' local instances had been converted to IRIS beforehand as well.

...to brand new server with iris2020.1

It's up to you, but why not install brand new IRIS on your brand new server? As you may notice, InterSystems is actively develop IRIS and usually doesn't release minor updated versions as it was in the case of Cache (e.g. IRIS 2020.1.1 vs Cache 2018.1.5). Choosing 2020.1, you are going to install the version which is near the end of its support cycle, see Minimum Supported Version Rules.

This (getFiles) method is marked as internal in Cache, and yes, it's typical internal as it's usage is relied on the strong internals knowledge :). Besides, it's hidden in IRIS, and its caller should be rewritten to achieve DBMS independence:

 ClassMethod ListDir2(path = "", wildchar = "*", recursive As %String(VALUELIST=",y,n") = "y", ByRef dirlist)
{
 pExtension=1
 pExtension(1)=wildchar

#if $zversion["IRIS"
 temp=$name(^IRIS.Temp)
#else
 temp=$name(^CacheTemp)
#endif
 
 pTempNode=$i(@temp)
 @temp@(pTempNode)
   
 ##class(%SQL.Util.Import).getFiles(path,.pExtension,pTempNode,recursive="y")
 dirlist=@temp@(pTempNode)
 @temp@(pTempNode)  ;zw dirlist
}

Bharathsimha,

your initial question should be reformulated as "how to find global's [main] database" because all namespaces have "equal rights" for any global which is visible from (= mapped to) them.

Julias is quite correct in his answering, but you should take into account that it concerns the global's main database only. If global subscript mapping is used, the full solution to get the list of all databases where the global is partially mapped is a more tricky task. If somebody is interested, I can write about how I solved it once.

Almost 15 minutes !!!

What about the second pass with the same ObjectScript code w/o restarting IRIS? 1.7GB is not too much to be stored in the file system cache, so it should be ~5 times quicker. Besides, it's well-known that Cache (IRIS) as a record reader is not so good as a block reader. Everybody knows that %GIF is 5-10 times quicker than %GI. I have the same experience with my own developments: processing files at the block level (read block#$$$BLOCKSIZE) with records parsing at the COS level is quicker than read it record by record. `5*5=25` is close to the time difference between your ObjectScript and Python code runs.

I've written this just to emphasize that we should love Python mostly for the power of its ecosystem, as Nigel wrote. As to speed, it would be better if you InterSystems guys do something to improve file i/o record level operations in IRIS engine...

if there will be an error this won't change the namespace back even with the "new $namespace" command

It would be still "%SYS" inside the `catch` block, so it's unsafe to call any code in its context. Even if you write something like this:

 ...
 try {
   new $namespace
   set $namespace="%SYS"
   ...
 } catch ex {   // process the error
   set sc=ex.AsStatus()
   do ..logErr(sc) // do some debug logging
 }
 return sc

and the ..logErr() call will be successful (generated .int code was not split into parts), the global where the log goes should be the same for all namespaces (e.g. mapped via %ALL pseudo-namespace). There are so many complications that it seems better to avoid any error processing inside the `catch` block above returning the error code. BTW, it sounds reasonable in any case, not only in this one associated with %SYS.

The key feature here is `new $namespace` command rather than the method of its changing, while `set $namespace="%SYS"` seems to be the preferred one as it is well documented and good looking.

I'd still use try / catch outside namespace changing as there can be security errors on attempt to do it. I mean something like this:

classmethod DoSomethingInSYS() as %Status
{
 set sc=$$$OK
 try { 
   new $namespace
   set $namespace="%SYS" 
   // do something, e.g. config change
 } catch ex {
   // process the error
   set sc=ex.AsStatus()
 }
 return sc 
}