On 1/10/2007 10:55 PM, Adam Cassar wrote:
> Hello,
> 
> We are currently running slony successfully in a mixed PG environment
> (v8 and v8.1).
> 
> With the release of PG v8.2 we want to upgrade all servers in our
> cluster to v8.2
> 
> I thought this would be quite simple - just dump and restore the db and
> everything should work....

That assumption was quite wrong. That is not the way how to upgrade a 
Slony cluster.

The database schema of your subscriber nodes (slaves) is in an 
inconsistent state from PostgreSQL's point of view. I am planning to get 
rid of this problem in the future, but it will be some time before it 
can be fixed. That means, that you cannot dump and restore a subscriber.

If you have the luxury to take an outage long enough to

     1.) uninstall slony completely
     2.) dump, upgrade PostgreSQL and restore the master
     3.) throw away and install new PostgreSQL version on all slaves
     4.) rebuild the entire slony cluster

do that.

Unfortunately not everyone has that luxury. If you are among those 
unfortunate people, here are the 12 pains of Christmas, Slony gave to you:

     1.) upgrade the cluster to the latest slony production release
     2.) Make your designated Backup node a leaf node
     3.) DROP that designated Backup node.
     4.) throw away and install new PostgreSQL version on that node.
     5.) STORE NODE for it and go through the full subscription process.
     6.) wait until it is completely in sync.
     7.) make it the only direct subscriber of the master, with all
         other nodes being cascaded from it (directly or sub-cascaded).
     8.) Switchover to the designated backup.
     9.) Drop the old master (which is now a subscriber).
    10.) Upgrade old master to an empty, new PostgreSQL version.
    11.) Subscribe it (again, wait until complete and cought up).
    12.) Switch back and reshape the cluster as needed.

The reason why this is so ugly and painfull is entirely that it is 
impossible to dump and restore a subscriber any way, that restores the 
system catalog into it's slony-corrupted state. That is why I am 
currently focused entirely on fixing that problem. Things would be a lot 
easier without that.


Jan

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