With the next update looming I thought this month's 'occasional thought'
might turn to the email subject line.

TL;DR particularly in production environments it's often advantageous to be
able to quickly move between releases.  WASD can make that straightforward.

In part this has been prompted by ongoing (occasional) comments from a
production site and how useful they find WASD's capacity to support multiple
versions and allow a rapid transition between them.  Primarily they're
thinking about regression due to some production issue undiscovered in their
pre-production testing regimen.

I recently asked to be reminded about their approach and received an
extensive reply.  I then set about integrating that into WASD Install and
Update document, only to (re)discover Section "5. Other Ways to Deploy", had
a subsection, "5.2 Multiple Installations".  You can view the current
(unrevised) version at

https://wasd.vsm.com.au/wasd_root/wasdoc/install/120install005.html#multipleinstallations

And reading through it, it's a useful starter for the 'thought' and the
documentation.  Needed a bit more emphasis on the multi-version support
angle.

Here I am going to quote (with permission) from the email reply to my
original response, "Gulp!", which is often my initial reaction to someone
else's production environment (or part thereof).  Edited for anonymity.

 "It may seem complicated, but once it is set up it is easy to use,
  and the main thing is that ************ feels that in the event of
  complications in the production environment after the introduction
  of a new version, they can quickly switch back.

 "It has also highlighted the problem of the installation of some of
  the VSI open source components.  Rather than installing in to a
  different subdirectory an installation of a new version basically
  overwrites the existing version.  That always presents a problem
  when you encounter behaviour in production which forces you to go
  back.  Oracle JDBC does it correctly in that it installs into
  different subdirectories and you have a SETUP procedure that
  basically defines certain logicals that point to the relevant
  subdirectory/version of JDBC.

 "That's one of the reasons that WASD is considered at ******** streets
  ahead of VSI products, of how it does things.  They are never nervous
  of introducing a new version into production, because it is no issue
  going back and then going forwards once a fix has been issued.
  After they have encountered a minor issue in their production 
  environment forcing them to go back, they often dispense with the
  staging in their test environment, as they can quickly test it in
  their production environment.

The document revised for 12.1 can be seen to be substantially the same with
slightly redirected emphasis and some new advice.

https://wasd.vsm.com.au/wasd_root/wasdoc/install/121install005.html#concurrentinstallations

The original reply referred to above, I will publish as a separate, following
email, rather than further clutter this one with considerable detail.  Also,
the detail is intended to be food-for-thought, rather than prescriptive.

Being a (mostly) 'practice what we preach' outfit here at WASD this is a list
of extant versions we can (somewhat) easily move between.

KLAATU$ DIRECTORY DKA100:[APPS]WASD_ROOT*

Directory DKA100:[APPS]

WASD_ROOT.DIR;1          1KB   6-OCT-2022 09:38:10.19
WASD_ROOT1000.DIR;1      1KB  12-APR-2020 14:08:22.96
WASD_ROOT1001.DIR;1      1KB  12-APR-2020 14:08:23.00
WASD_ROOT1002.DIR;1      1KB  12-APR-2020 14:08:23.05
WASD_ROOT1003.DIR;1      1KB  12-APR-2020 14:08:23.09
WASD_ROOT1010.DIR;1      1KB  12-APR-2020 14:08:23.14
WASD_ROOT1011.DIR;1      1KB  12-APR-2020 14:08:23.18
WASD_ROOT1020.DIR;1      1KB  12-APR-2020 14:08:23.23
WASD_ROOT1030.DIR;1      1KB  12-APR-2020 14:08:23.29
WASD_ROOT1040.DIR;1      1KB  12-APR-2020 14:08:23.33
WASD_ROOT1041.DIR;1      1KB  12-APR-2020 14:08:23.42
WASD_ROOT1042.DIR;1      1KB  12-APR-2020 14:08:23.45
WASD_ROOT1100.DIR;1      1KB  12-APR-2020 14:08:23.50
WASD_ROOT1101.DIR;1      1KB  12-APR-2020 14:08:23.54
WASD_ROOT1102.DIR;1      1KB  12-APR-2020 14:08:23.59
WASD_ROOT1110.DIR;1      1KB  12-APR-2020 14:08:23.64
WASD_ROOT1111.DIR;1      1KB  12-APR-2020 14:08:23.69
WASD_ROOT1120.DIR;1      1KB  12-APR-2020 14:08:23.75
WASD_ROOT1130.DIR;1      1KB  12-APR-2020 14:08:23.80
WASD_ROOT1140.DIR;1      1KB  12-APR-2020 14:08:23.85
WASD_ROOT1141.DIR;1      1KB  12-APR-2020 14:08:22.90
WASD_ROOT1150.DIR;1      1KB  24-JUL-2020 03:36:30.64
WASD_ROOT1151.DIR;1      1KB  30-AUG-2020 14:25:05.62
WASD_ROOT1200.DIR;1      1KB   4-NOV-2021 09:38:00.33
WASD_ROOT1201.DIR;1      1KB   5-OCT-2022 10:18:20.49

Total of 25 files, 26KB

Of course, the WASD_ROOT.DIR is the pre-release v12.1 still under development
and testing.

PS.  The complete "collection of occasional thoughts …" (so far)
     https://wasd.vsm.com.au/other/#occasional