There are a few instances where the release notes seem to indicate that the administrator should use pg_dump to upgrade a database so that improvements on btree can be available.
Here are they: 1. >In new btree indexes, the maximum index entry length is reduced by eight bytes, to improve handling of duplicate entries (Peter Geoghegan) - > This means that a REINDEX <https://www.postgresql.org/docs/12/sql-reindex.html> operation on an index pg_upgrade'd from a previous release could potentially fail. - - 2. >Improve performance and space utilization of btree indexes with many duplicates (Peter Geoghegan, Heikki Linnakangas) >... >Indexes pg_upgrade'd from previous releases will not have these benefits. 3. >Allow multi-column btree indexes to be smaller (Peter Geoghegan, Heikki Linnakangas) >... >Indexes pg_upgrade'd from previous releases will not have these benefits. My questions are: 1. Is this a current limitation of pg_upgrade that will be dealt afterwards? 2. Are we going to see more of such cases were pg_upgrade leaves the database incompatible with newer features. 3. What's the recommendation for administrators with databases that are too large to be upgraded with pg_dump?
