[Pkg-postgresql-public] postgresql 8.2 packaging

[Peter Eisentraut]

Martin Pitt wrote:
> Hello Peter,
> 
> Peter Eisentraut [2009-03-02 11:03 +0200]:
>> Btw., there is another matter that we need to think about for the 
>> future.  PostgreSQL 8.4 will probably have in-place upgrade support. 
>> But that (probably) only works for upgrading to the next release.
> 
> What does that mean in particular? An 8.5 server can understand the
> data directory of 8.4 and upgrade it on the fly? But it doesn't
> understand 8.3?
> 
> If that's planned anyway, why is it significantly more difficult to
> keep backwards compatibility for more releases?

In-place upgrade involves two things: Upgrading the system catalogs and 
upgrading the binary data format.  If you recall the old pg_upgrade 
approach: It dumped the system catalogs in SQL format, restored them 
into the new server, and moved the data files across.  This is basically 
the way it still works.  The data file format hasn't actually changed 
between 8.3 and 8.4, so performing this upgrade from 8.3 to 8.4 isn't 
difficult.  (Note: The tool is called pg_migrator and is on pgfoundry. 
We should package it sometime.)

If the binary file format were to change in 8.5, then, assuming the 
development team sticks to this plan, 8.5 will also be able to read the 
old 8.4 format.  And thus also the 8.3 format, because it's the same. 
What I don't know, however, is if the catalog upgrade will be supported 
over two versions.  But the answer to the question "Why is it more 
dificult" is basically about manpower.  We'll see what happens.  And of 
course we can speak up and affect the outcome.