Tom Lane wrote: > Alvaro Herrera <alvhe...@alvh.no-ip.org> writes: > > It seems pretty clear to me that we should somehow transfer stats from > > the old server to the new one. Shouldn't it just be a matter of > > serializing the MCV/histogram/ndistinct values, then have capabilities > > to load on the new server? > > The reason pg_upgrade hasn't done that in the past is not wishing to > assume that the new version does stats identically to the old version. > Since we do in fact add stats or change stuff around from time to time, > that's not a negligible consideration.
Sure, but the new version can probably limp along with incomplete stats until the next natural ANALYZE runs -- the system is operational in much shorter time than if you have to make it all wait for the post-upgrade full-database ANALYZE run. The serialization step is so that the underlying representation doesn't have to remain identical -- surely the new server would be able to represent whatever the old server was able to, regardless of any improvement made. -- Álvaro Herrera https://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
