Date: Tue, 31 Aug 2004 23:35:18 -0400
On 8/31/2004 9:38 PM, Andrew Rawnsley wrote:
> On Aug 31, 2004, at 6:23 PM, Marc G. Fournier wrote:
>
>> On Tue, 31 Aug 2004, Josh Berkus wrote:
>>
>>> Andrew,
>>>
>>>> If I were loony enough to want to make an attempt at a version
>>>> updater
>>>> (i.e. migrate a
>>>> 7.4 database to 8.0 without an initdb), any suggestions on where to
>>>> poke first? Does a
>>>> catalog/list of system catalog changes exist anywhere? Any really
>>>> gross
>>>> problems immediately
>>>> present themselves? Is dusting off pg_upgrade a good place to start,
>>>> or
>>>> is that a dead end?
>>>
>>> Join the Slony project? Seriously, this is one of the uses of
>>> slony. All
>>> you'd need would be a script that would:
>>>
>
> I thought of this quite a bit when I was working over eRServer a while
> back.
>
> Its _better_ than a dump and restore, since you can keep the master up
> while the
> 'upgrade' is happening. But Mark is right - it can be quite
> problematic from an equivalent
> resource point of view. An in-place system (even a faux setup like
> pg_upgrade) would be
> easier to deal with in many situations.
| There is something that you will not (or only under severe risk) get
| with an in-place upgrade system. The ability to downgrade back in the
| case, your QA missed a few gotchas. The application might not instantly
| eat the data, but it might start to sputter and hobble here and there.
|
| With the Slony system, you not only switch over to the new version. But
| you keep the old system as a slave. That means that if you discover 4
| hours after the upgrade that the new version bails out with errors on a
| lot of queries from the application, you have the chance to switch back
| to the old version and have lost no single committed transaction.
Just asking: how far back in time Slony can "downgrade" or keep the older
servers in "slavery"? 6.5? I haven't tried it yet, hence, the question.
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