Re: application online upgrade strategy

["Merlin Moncure" <mmoncure(at)gmail(dot)com>]

On 5/23/07, lest mitsui <lestcdn(at)hotmail(dot)com> wrote:
> Does anyone have an idea on where to turn for information/research papers on
> online application upgrades? I am well-versed in offline upgrades, but I am
> now faced with customer requirements for transparent software upgrades of
> our application server/services -- and what possible solutions are there for
> software upgrades with co-requisite schema changes.

In theory, if your application is 100% database driven (with a thin
rendering middleware), you can update your app with a single
transaction.  The database gives you all the tools you need...you can
lock the appropriate structures and postgresql ddl is gloriously
transactional.

The problem often lies with the application itself.  Since most apps
are not 100% database driven, you have to worry about syncing the
application with the database.  In this case, I'd treat the problem
like a classic database problem...begin a database transaction, lock
the appropriate structures, update the relevant application structures
(taking care to handle rollback conditions if necessary), and commit
the transaction.

If your app is minimally database driven, common in ORM style
development...well, good luck! :-)

merlin