Re: Upgrading a database dump/restore - Mailing list pgsql-hackers

> On Mon, Oct 09, 2006 at 11:50:10AM -0400, Mark Woodward wrote:
>> > That one is easy: there are no rules.  We already know how to deal
>> with
>> > catalog restructurings --- you do the equivalent of a pg_dump -s and
>> > reload.  Any proposed pg_upgrade that can't cope with this will be
>> > rejected out of hand, because that technology was already proven five
>> > years ago.
>
> <snip>
>
>> Dumping out a database is bad enough, but that's only the data, and that
>> can takes (mostly) only hours. Recreating a large database with complex
>> indexes can take days or hours for the data, hours per index, it adds
>> up.
>
> I think you missed the point of the email you replied to. *catalog*
> changes are quick and (relativly) easy. Even with 10,000 tables, it
> would only take a few moments to rewrite the entire catalog to a new
> version.
>
>> If it is a data format issue, maybe there should be a forum for a "next
>> gen" version of the current data layout that is extensible without
>> restructuring. This is not something that a couple people can go off and
>> do and submit a patch, it is something that has to be supported and
>> promoted from the core team, otherwise it won't happen. We all know
>> that.
>
> Actually, the data format is not the issue either. The tuple structure
> hasn't changed that often. What has changed is the internal format of a
> few types, but postgresql could support both the old and the new types
> simultaneously. There has already been a statement from core-members
> that if someone comes up with a tool to handle the catalog upgrade,
> they'd be willing to keep code from older types around with the
> original oid so they'd be able to read the older version.

That's good to know.

>
>> The question is whether or not you all think it is worth doing. I've
>> done
>> consulting work for some very large companies that everyone has heard
>> of.
>> These sorts of things matter.
>
> People are working it, someone even got so far as dealing with most
> catalog upgrades. The hard part going to be making sure that even if
> the power fails halfway through an upgrade that your data will still be
> readable...

Well, I think that any *real* DBA understands and accepts that issues like
power failure and hardware failure create situations where "suboptimal"
conditions exist. :-) Stopping the database and copying the pg directory
addresses this problem, upon failure, it is a simple mv bkdir pgdir, gets
you started again.

If you have a system on a good UPS and on reliable hardware, which is
exactly the sort of deployment that would benefit most from an "in place"
upgrade. There is no universal panacea where there is 0 risk, one can only
mitigate risk.

That being said, it should be the "preferred" method of upgrade with new
versions not being released untill they can migrate cleanly. A
dump/restore should be a last resort. Don't you think?