RE: Restore on different version

Excellent, thank you very much Martin. I was looking for some
documentation on this, but couldn't find any, except for the migration
guide that says:

"Warning: Backups that you make under older versions of your database
server are not compatible with the newer version. Do not try to restore
these backups to the newer version."


I really appreciate the reply.

Dirk


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From: informix-list-bounces@xxxxxxxx
[mailto:informix-list-bounces@xxxxxxxx] On Behalf Of Martin Fuerderer
Sent: 30 August 2006 11:25 AM
To: Dirk Moolman
Cc: informix-list-bounces@xxxxxxxx; informix-list@xxxxxxxx
Subject: Re: Restore on different version

Hi,

in order to implement new functionality for new versions of
IDS it is often necessary to change the structure of the data
on the disk. I.e. the data on the disk becoimes a new
format. This data is not just the user data, but it is data
that is needed for IDS's internal house-keeping.
Often you can hear the term "disk structures" describing
this specific format of the data on disk.
This data in its specific format is what is backed up when
you do a backup/archive (using ontape/onarchive/onbar
or external backup).

To make restore in a newer version of IDS fully backward
compatible to backups from older versions, all the data
formats (i.e. the "disk structures") would have to be versioned.
That way the restore would then have to recognize the
particular version of backup data and then act upon it
accordingly.

This would pose considerable overhead, and the philosophie
with IDS always was to not do this, because of the tremendous
overhead involved. As a result, there is no backward
compatability for restoring older versions' backups.

Without this backward compatibility, the newer version
simply does not know to differently interpret and handle data that
has an older version's format, because the "disk structures"
simply do not match. So the newer version interprets the
older data according to the newer format, i.e. the new
"disk structures" are assumed implicitely and then applied.
This then causes failures at arbitrary points during ongoing
processing. And there is nothing that can be done about it.

Now, if between two versions there were no changes in the
"disk structures", or only such changes that don't affect a
particular system (e.g. because not utilizing a certain feature),
then a restore might work. However, strictly speaking this is
a (lucky ?) coincidence and cannot be used to conclude that
this should work for other version combinations or even a
different instance backup. Therefore the general and correct
statement is, that these things are not support.

Usually it should be possible to restore using the old version
and then migrate forward to the new version, possibly in
several steps. Of course if this would involve OS upgrades
as well, then it is not really an easy thing to do.

Regards, also to your manager :))
Martin
--
Martin Fuerderer
IBM Informix Development Munich, Germany
Information Management

Informix URLs list: http://home.arcor.de/mfu1/informix/urls.html
IBM Information On Demand Global Conference
October 15-20, 2006, Anaheim, California
see http://www.ibm.com/events/informationondemand

informix-list-bounces@xxxxxxxx wrote on 30.08.2006 09:20:56:

Hi, I was asked to try a restore for a client on version 7.31, using a
7.30 backup. I told them that this was not supported, but they
insisted that I do the restore and prove that it doesn't work.

So I set up a database on another machine, took the 7.30 backup (that
was done on an HP opsys) and tried to restore it on the 7.31 database
(that is on a Solaris opsys), with the following result:


Continue restore? (y/n)y
Do you want to back up the logs? (y/n)n
Physical restore failed - buc_fe.c : Archive API processing failed at
line 740 for msgtype

Program over.



My manager is still not happy that this doesn't work, and says I
didn't
try hard enough. How can I respond to this - seriously ?


Dirk


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of
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way be construed as the views of Agility (Pty) Ltd, except where the
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