Re: root page 3 of index "pg_class_oid_index" has level 0, expected 1 - Mailing list pgsql-general

On Thu, Nov 14, 2019 at 08:26:48AM +0100, Laurenz Albe wrote:
> If you have data corruption, you shouldn't use pg_upgrade to upgrade.
> pg_dumpall / psql is the way to go.

Please refer to this wiki page:
https://wiki.postgresql.org/wiki/Corruption

If you have a cluster in such a state, you have risks of having a
corruption which has spread, and you should not reuse this data folder
as-is.  You can think of this REINDEX as a short-term solution to
retrieve as much of your data as you can so as you can dump it, and
then restore it into a safer location.  For corruptions with system
indexes, you also have the option of using ignore_system_indexes.
--
Michael