On 8/8/12 5:29 PM, Alvaro Herrera wrote:
I think those 14 is a bit of a made-up number. Several of those steps
are about building pg_upgrade, not actually using it. And there are
some that are optional anyway.
Compare the pg_upgrade instructions
http://www.postgresql.org/docs/9.2/static/pgupgrade.html
to the old pg_dump-based upgrade instructions that we used to give people:
http://www.postgresql.org/docs/8.4/static/install-upgrading.html
They are about the same in complexity (the pg_dump approach didn't talk
about updating statistics or removing the old cluster, so it has less
steps).
So I don't think the number of steps is a problem at all. They could be
simplified a little bit more, of course.
What's more of a problem in my mind is the "unknown unknowns" in
pg_upgrade's approach. In the pg_dump/restore approach, you knew that
if the dump succeeded and the restore succeeded, your new database was
very likely good. The only problem could be that pg_dump forgot to dump
something altogether, or that there is a general problem in executing
SQL commands, both of which would be obvious problems. With pg_upgrade,
however, you never know whether your new instance is good. You could
notice problems months later. That's a really tough proposition.
Another thing worth considering is to have pg_upgrade init, stop and
start clusters as necessary instead of requesting the user to do it.
I think this is two less steps.
Then you'd need to expose the entire pg_ctl shutdown mode logic through
pg_upgrade, which might not make things simpler.
I wonder if things would be facilitated by having a config file for
pg_upgrade to specify binary and PGDATA paths instead of having awkward
command line switches.
If you want to do that, why not write a shell script? That's what they
are for.
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