"David P. Hopfensperger" <[log in to unmask]> wrote:
 
We will be embarking on a large database conversion soon and would like to
leave our largely COBOL/ALLBASE/SQL application available for as much of the
conversion as possible.  The conversion will require unloading and reloading
virtually every table in the DBE.  What I'm wondering is:
 
1.  Do any of you, or your clients, have experience with database conversions
in a 24x7 environment?  If so, how do you provide application availability
while converting the database?
There is obviously a cost to pain ratio that your users must decide upon.  If the
cost of being without access to the data for the estimated amount of time it would
take (to do the conversion sucessfully, or the amount of time it would take to attempt
the conversion, fail, and then recover) is greater than the costs to the company of
any of the alternatives, then you have several options...
2.  Would something like online ALLBASE/Replicate help?  How about Mirrored
Disk?  Could we provide update-access to the "mirrored/shadowed" DBE while
converted the "real" DBE?
Allbase/Replicate could either be used.  I'm not sure about the mirrored disc though.
When you split your mirrors, your pretty limited in what you can do with the offline
drives (normally, backing them up).  I don't think you could use it to perform your
conversion.  Here is the Allbase/Replicate scenario:
      Allbase/Replicate can be setup relatively painlessly if (and I believe this is your case)
     you want 100% of the 'user data' shadowable (my apologizes to Webster!).  The two
     cent outline would be to temporarily shutdown access to your existing DBE, and
     turn on audit logging with archive log files (the amount of work here depends on
     what your currently setup for).  While your shutdown, get a backup of the database
     (or start an online backup).  Bring things backup, while you get the database restored
     whereever it is you want to put it.  Restore the DBE (sans log files) and do a startdbe
     newlog changing the WSLID on this DBE.  Restart archive logging here too.  Now start
     the shadow jobs, and the secondary copy of the database will pickup all new transactions
     that have occured since the backup.  Stop the shadowing jobs whenever, and your ready
     to go.
      At this point, you can either use this DBE for you conversion, or you can switch your
     users off the original and onto this one, using the original for the conversion.  Things
     to keep in mind here are what you conversions "really are".  If you are going to make
     changes to a table that will continue to receive updates on the other DBE, your out of
     luck (unless your simply adding columns that accept nulls at the end of the table).
      When you perform the conversion, remember to "disable audit logging" on the
     DBE your working on (you don't want to try and shadow your changes).  When your
     done, restart the shadowing jobs, and get caught back up again.  If you have the spare
     horsepower and disc for this, it works great.  You need to make sure that you have
     plenty of log space available on the DBE being updated to handle the load for the
     duration of your outage.  If you end up clobering your sync point, you have to
     start from scratch! (which by Murphy's law says that it would happen after 39.5 hours
     of a 40 hour process!).
 
3.  If we can't provide update access, how about read-only access?  Would that
work?
If you don't need to update the data, then just get a backup of your DBE after all of the
updating has been completed, restore it somewhere (again without the log files), do a
startdbe newlog, and convert away.  When you done, back it up, shutdown your
original DBE, and restore the new DBE (redoing the log files yet again).  Unfortunately,
your down for the duration of the restore and rebuild of the log files.
 
Any help would be greatly appreciated.  Either post a follow-up, or email me
directly.
 
Oh, BTW, we are a large mixed HP3000, IBM MVS shop.  The conversion involves
unloading data from the ALLBASE DBE and merging it with data unloaded from
several IMS databases.
 
Once you get this "merged" data, what then?
 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
David Hopfensperger [log in to unmask]
http://www.ilstu.edu/~dphopfe
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
 
If you have any other questions, feel free to give me a call or drop some email
 
Michael L Gueterman
Easy Does It Technologies
[log in to unmask]
voice: (509) 946-6179
fax:     (509) 946-1170