[CentOS-devel] Upgrading postgresql (Re: CentOS/RHEL 5.3)

Thu Jan 22 17:48:11 UTC 2009
Jeff Johnson <n3npq at mac.com>

On Jan 22, 2009, at 12:25 PM, Les Mikesell wrote:

> Joshua Kramer wrote:
>> Any major database version upgrade requires the attention of a  
>> qualified
>> DBA who knows how to test data and applications against the new DB
>> version, and then dump/upgrade/restore.
>> For example, PostgreSQL introduced some minor syntactical  
>> differences with
>> 8.3.  If your application uses the features affected by these  
>> changes, it
>> would be impossible to simply 'dump/restore' without some massaging  
>> of the
>> data and the application.
>> PostgreSQL does ship with a dumper, pg_dump.  If you have the current
>> version of postmaster, then you use pg_dump to connect to that and  
>> dump
>> your data in a version-agnostic format.  IMHO, the effort of  
>> writing a
>> standalone dumper that can recognize all the old file formats is  
>> not worth
>> it, because it is a mistake to delete the old version of postmaster  
>> off
>> your system before you've done a dump of the database.
> So how do you package such a thing in RPM so it can permit both new  
> and
> old instances to run simultaneously while you do all of this required
> testing?  I suppose these days virtualbox is an almost-reasonable  
> answer
> but it just seems wrong to have a system that by design doesn't let  
> you
> test a new instance before replacing the old one.

Historical note:
	A long time ago (RHL 5.2 iirc) transparent upgrades
	of postgres databases was attempted within *.rpm
	packaging. The result was a total disaster.

Don't attempt the database conversion while upgrading is the moral.

Arrange paths in postgres packaging so that both old <-> new utilities
are available when needed. That can most easily be done by
including whatever old utilities are needed in the new package
so that the conversion can be done after the old -> new upgrade.

Alternatively, one can also attempt multiple installs of postgres
side-by-side kinda like kernel packages are done.


73 de Jeff
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