Question
Adel Elsayed · Jul 21

What is the best way to export a global or a table to a file?

in order to do analysis on huge data volumes, it is better to take you data to a separate machine for analysis away from the operational machine, so trying to write huge globals or tables into files as is would take a huge space, what could be a solution or best practice ?..in python for instance, there is the pickling option (serializes data to byte string and saves it to a file) to save space, what could be best in object script ?

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from my point of view, writing and reading from a flat-file is a good one. but instead of that if you take backup whole database and use it wherever you want.  because it would be a generic one. do you face any problems with the backup?

  1. Whatever you do it affects the operational machine as you have to read through the whole Table/Global
  2. For Table it can be a simple SELECT * FROM TABLE  with the option to select columns of interest
  3. For Global  use $system.OBJ.Export(<globalname>.GBL,<filename>)  as XML.

 Of course, if you have a Shadow instance of your operational machine you can do it there and avoid the load on the primary machine.
Eventually, you can run there all analyses without export at all.

Can one export a specific node as XML via $system.OBJ.Export or otherwise?

Anna - yes, when you build your array of items to export, you can include expressions like:

set items("myGlobal(""x"").GBL") = ""

set status = $system.OBJ.Export(.items, myFile, myOptions)

... and this will export ^myGlobal("x").

One more question if I may: I try to exclude global subnodes but so far unsuccessfully. Is it possible?
This correctly exports the corresponding node only: items("SOMEGLOBAL(""ABC"",""XYZ"",""USERFORM_ATEST"").GBL") = ""
Now if I try to exclude this node from the SOMEGLOBAL like this, items("SOMEGLOBAL.GBL",'"SOMEGLOBAL(""ABC"",""XYZ"",""USERFORM_ATEST"").GBL") = "", it does not exclude it. There is a barely visible single negating quote in the beginning of the second item.

I don't think this syntax works. I think the exclusion is for matching against wild cards, for example if you wanted to export all the globals called some*.gbl but exclude one or more of them. I don't think it deals with subscripts.

You may need to merge your global into a temporary global, kill the subnodes you want to exclude, export, and then merge the temporary global back to restore them. (or something similar)

I understand that this is probably not an option if the data is huge. Maybe InterSystems support (WRC) can help.

You can also use a reporting async or perhaps an ECP application server, depending on what analysis you are doing. 

Hi.

As the main objective is not to overload the server any of the solutions presented will overload the production server. Whether performing a backup, exporting data to file, etc. ​Especially if it is a repetitive, constant task with a large volume of data.

If your product license allows it, it is recommended to use a shadow server. Adopting a shadow server will redirect the processing effort from any adopted solution to another machine.
https://docs.intersystems.com/latest/csp/docbook/Doc.View.cls?KEY=GCDI_s... 

If you plan to have IRIS analytics server one of the options is to setup the second server as disaster recovery mirror member - it's an async mirror member.

This will let you to have a server that is almost always automatically up-to-date  and the server is ready for analytics queries load

If your other system is also a Cache or IRIS server, there is a mirroring options called a reporting async that exists for this specific purpose. If you've got multiple servers and need to consolidate that data for reporting purposes, a reporting async can be a part of up to 10 mirrors to help you bring that data together, too.