Re: psql backward compatibility

On Wed, Nov 18, 2020 at 9:16 AM Adrian Klaver <adrian(dot)klaver(at)aklaver(dot)com>
wrote:

> On 11/18/20 8:05 AM, Stephen Haddock wrote:
> > Hello,
> >
> > When upgrading an older version of postgres, version 8.4 for example, to
> > a newer version such as 9.6, does the data have to be migrated
> immediately?
> >
> > It looks like the recommended method is to dump the data, upgrade,
> > initialize a new cluster, and then restore the dumped data into the
> > newer version. My question is whether the data dump and restore must be
> > done immediately. It appears that 9.6 is able to run against the older
> > cluster (DB service starts, queries work, etc), and the data could be
>
> Hmm, missed that. As David said that should not happen and if you are
> running a new binary against an old cluster then you will get corruption.
>
>
Actually, upon re-reading I suspect you are more likely correct. Depending
on the package/installer both 8.4 and 9.6 are both able to run on the
server simultaneously - on different ports. Upgrading PostgreSQL to 9.6
only installs the database programs and, usually, a default cluster (using
the next available port number) having a "postgres" database (it's not
really an upgrade if the major version changes, it's a new install).
Separately, the DBA must initiate an upgrade of clusters (or dump/reload of
individual databases) that they wish to run under the newly installed 9.6
version.

David J.