Jerry, * Jerry Sievers (gsiever...@comcast.net) wrote: > Bruce Momjian <br...@momjian.us> writes: > > I agree, but I am not sure how to improve it. The big complaint I have > > heard is that once you upgrade and open up writes on the upgraded > > server, you can't re-apply those writes to the old server if you need to > > fall back to the old server. I also don't see how to improve that either. > > Hmmm, is it at least theoretically possible that if a newly upgraded > system were run for an interval where *no* incompatible changes to DDL > etc had been done... > > ...that a downgrade could be performed? > > Er, using a not yet invented pg_downgrade:-)
The short answer is 'no'. Consider a case like the GIN page changes- as soon as you execute DML on a column that has a GIN index on it, we're going to rewrite that page using a newer version of the page format and an older version of PG isn't going to understand it. Those kind of on-disk changes are, I suspect, why you have to set the "compatibility" option in the big $O product to be able to later do a downgrade. > That is, since higher version knew enough about lower version to > rejigger everything... just maybe it could do the reverse. That might work if you opened the database in read-only mode, but not once you start making changes. Thanks! Stephen
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