Re: RHEL OS upgrade from 6.7 (Current version) to 8 version for Postgresql database

ram pratap maurya <rampratap0000(at)gmail(dot)com> writes:
> we are planing to RHEL OS upgrade from 6.7 (Current version) to 8 version.

> currently postgresql-12.6 version running on the server , we have upgraded
> OS on test DB server from 6 to 8 version during OS upgrade
> postgresql-12,11 and other package is removed and Postgresql is not
> started. that why my DB is crashed , can you please suggest what is best
> way to upgrade OS.

There are a couple of big gotchas you need to think about:

* RHEL8 is systemd based, while 6 still used the old initscript startup
code. This means that the way to get a daemon process launched is
completely different. So PG packages built for RHEL6 *will not work*.
You need to get a server package that is systemd-ready, and that means
one that was explicitly built for RHEL8. (Maybe a RHEL7 one would
work, not sure. But it is zero surprise that the packages you listed
aren't working.)

* RHEL8 incorporates new locale data [1]. This means that non-English
text is rather likely to sort differently than it did before, which in
turn means that indexes on text columns will be corrupt if you try to
upgrade in place. While you could REINDEX them after updating, this
might be a good reason to do a dump-and-reload instead of trying to
pg_upgrade.

In short, this is no minor upgrade you're contemplating.

regards, tom lane

[1] https://wiki.postgresql.org/wiki/Locale_data_changes