Re: replication for hot-standby?

Hannes Dorbath wrote:

> Yes, it does in /some way/, but it's quite hackish and error prone.. :/

It's far from hackish, and only error prone if you don't follow best
practices (ie:fireing DDL changes through slonik without testing them on
_all_ nodes first).

>
>> If there is anything broken about the script, or about how it
>> executes on a particular node, this will cause the slon daemon for
>> that node to panic and crash. If you restart the node, it will, more
>> likely than not, try to repeat the DDL script, which will, almost
>> certainly, fail the second time just as it did the first time.
>
>
>> Unfortunately, this nonetheless implies that the use of the DDL
>> facility is somewhat fragile and fairly dangerous.
>
>
>> If your applications do not have fairly stable SQL schemas, then
>> using Slony-I for replication is likely to be fraught with trouble
>> and frustration.
>
>
> Sorry, this really doesn't sound like something I'd like to use in a
> production environment..
>
It totally depends on your enviornment. We use Slony in a 24x7x365
production enviornment. Usage requires that you know what your doing,
and fair amount of care and planning when using it. But Slony was
never designed with the intent of being a click and forget type system.

If you have environement where the schema is not stable, replicating
with Slony will likely take a lot of work, but can be done safely. If
you don't have control over your schema changes (ie a web hosting
environement where the end user can change the schema), it's certainly
out of the picture. In that scenario, I think you're going to have a
hard time finding a replication engine that will let you have a hot
standyby.

--
Brad Nicholson 416-673-4106
Database Administrator, Afilias Canada Corp.