Re: Slightly OT.

Alexander Staubo wrote:
> On 6/1/07, Jeff Davis <pgsql(at)j-davis(dot)com> wrote:
>> On Fri, 2007-06-01 at 17:00 +0200, Alexander Staubo wrote:
>> > the projected Slony-II design, but the setup seems dead simple, and
>> > from the docs I have found it seems to transparently replicate schema
>> > changes, unlike Slony-I. So that's something.
>>
>> To be fair to Slony-I, the fact that it does not replicate DDL is a
>> feature, not a bug. It's table-based, which is a very flexible design.
>
> I fail to see how that's an excuse not to replicate DDL. If I run
> "alter table" on the master, there is no reason whatever that this
> command cannot be executed on all the slaves -- which is what I would
> expect of a replication system.

As the owner of a company that actually actively developing a
replication system and has for years... I suggest you start putting your
code where your words are.

This is not nearly as simple as it seems. There is a reason that Slony
attempts to do it in user space instead of postgresql space.

Joshua D. Drake

>
> To put it differently: A slave's table is a replica of the master's
> table; if I alter the master table, and the slave is not updated to
> reflect this change, then the slave table is no longer a true replica,
> and the system has failed its core purpose, that of *replicating*.
>
> I could be wrong, but I believe Slony fails at this because it is
> trigger-based and simply cannot detect DDL changes.
>
> Alexander.
>
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