Обсуждение: Need some info.

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On Thu, Jan 10, 2008 at 01:07:09PM +0530, Suresh Gupta VG wrote:
> We are upgrading the pgsql from 7.4.2 to 8.2.5 on Solaris 9 Spark
> machine, I had downloaded the sources also. I had gone through the
> instalation documents too. I could not find the procedure to rollback
> the new version, if the new version does not support our application.

This is a difficulty, yes.

> 1)       Can we do rollback if required after complete installation??

Generally, major releases are binary incompatible.  If you find your upgrade
fails, you can of course continue to use your old installation (so don't
delete your old data directory!).  But if you've processed transactions in
the new system, they'll be lost to the old installation, and then you're
hosed.

What you _can_ do, however, is install Slony.  You might need to upgrade
your 7.4 version to do this -- the version you have is very old, and there
are some bugs that might affect Slony (I don't remember).  Not to worry --
that shouldn't be a big deal (it's not a dump and restore).  But it will
require some planning and such.  What you do, in this case, is install Slony
on 7.4, add the 8.2.x replica, and let it catch up.  When it's time to do
your upgrade, you do a switchover (not a failover) and cause the 8.2.x to
replicate to your 7.4.x installation.  Now transactions that happen in 8.2
will also appear in 7.4, and if something blows up, you can switch back.

This feature is an explicit design goal of Slony, and Afilias has used it in
production, so I can be confident it works.  But you need to do a lot of
planning and testing.  It isn't something to do in a couple days' time.

> 3)       If we do the installation in the other directory which doesn't
> contain old version. Does it solve our problem

Sort of; see above.

A

• in plain sql format
• File system base ( remember to shutdown postgresql before taking backup)
  
• pg_dump