Tom Lane wrote:
> The system tables are not the problem. pg_upgrade has shown how we
> can have cross-version upgrades no matter how much the system catalogs
> change (a good thing too, because we cannot freeze the system catalog
> layout without bringing development to a standstill). A schema-only
> dump and restore is cheap enough that there's no real reason to look
> for any other solution.
> Changes in the on-disk representation of user tables would be harder to
> deal with, but they are also much rarer (AFAIR we've only done that
> twice: WAL required additions to page and tuple headers, and then there
> were Manfred's space-saving changes in 7.3). And as of 7.3 there is a
> version field in page headers, which would in theory allow for a
> page-at-a-time update process to work.
> There isn't any fundamental reason why we cannot have a pg_upgrade
> utility; claiming that there is something wrong with how we handle
> catalog changes misses the point. The point is that *someone would
> have to do the work*. Unless someone wants to step up and volunteer,
> there's little value in discussing it.
pg_upgrade does work, assuming there are no changes to the index or heap
file formats. (However, I now need to update it for schemas.) However,
the last time I worked on it for 7.2, no one was really interested in
testing it, so it never got done. In fact, there was a bug in the
handling of clog or wal files, but I didn't find out about it until long
after 7.2 because no one was using it.
Is pg_upgrade too hard to run? Is no one really interested in it?
Bruce Momjian | http://candle.pha.pa.us
pgman(at)candle(dot)pha(dot)pa(dot)us | (610) 359-1001
+ If your life is a hard drive, | 13 Roberts Road
+ Christ can be your backup. | Newtown Square, Pennsylvania 19073
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