Re: Major upgrade of PostgreSQL and MySQL

From: Stephen Frost <sfrost(at)snowman(dot)net>
To: Patrick Dung <patrick_dkt(at)yahoo(dot)com(dot)hk>
Cc: "pgsql-general(at)postgresql(dot)org" <pgsql-general(at)postgresql(dot)org>; Ivan Voras <ivoras(at)freebsd(dot)org>; Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>; Stephen Frost <sfrost(at)snowman(dot)net>
Sent: Saturday, September 14, 2013 1:13 AM
Subject: Re: [GENERAL] Major upgrade of PostgreSQL and MySQL

On Friday, September 13, 2013, Patrick Dung wrote:
>What?  That's absolutely *not* required for pg_upgrade to work.  In
>>general, I would recommend that you make a copy of the database, but
>>it's certainly not required.
>
>I mean the old version and new version would need to take up disk space on the server.
>Thus roughly doubled the disk space used.
>

>And I'm telling you that pg_upgrade does NOT require that. It has a mode which allows an in-place upgrade (using hard links) that only >requires a bit of extra disk space- certainly no where near double on a database of any size. 

Thanks to Stephen for pointing out using link with pg_upgrade.

I read the pg_upgrade section again: http://www.postgresql.org/docs/9.3/static/pgupgrade.html

1. In the past, I have an impression that it requires double of the database size.
Because the manual present in a way that it 'must' need to hold the old and new database cluster.
But it does not mention the benefit of using hard links to save disk space and speed.
I think the documentation could put a note at the beginning for new users.

2. Also I think the documentation should provide more info for users that use packages.
Most likely the system would do dependency checking and may refuse two install two versions at the same time.
So uses need to install the new version in another location.
More documentation should be provided for this part (e.g for users using Linux rpm/deb or FreeBSD ports).

3. But the way, if users is using Windows, is the link option still works?

Thanks,
Patrick