Hi Bill,

thank you for your detailed reply. There is yet another issue
that I need to be aware of: network partitions. Since I can't
ensure that all sites are connected directly, I belive that this
kind of failure is a possible scenario.
Do you have any idea, how Slony deals with that kind of issue?

Best regards,
Michael

On 20.04.2008, at 18:31, Bill Moran wrote:

> Michael Gruetzner <mgruetzn at HTWM.De> wrote:
>>
>> Hi,
>>
>> I have to meet the challenge of creating a wide area database  
>> cluster.
>> Since
>> I have made some good experiences with Slony-1 in the past, I'm
>> wondering
>> if it would also work with wide-area networks. Of course, bandwidth
>> and latency
>> are main issues but also network failures.
>> The Slony-1 documetation says that it might not be suitable if some
>> nodes may
>> fail oftenly but it does not explain how slony deals with such
>> failures (maybe someone
>> can explain this to me?).
>>
>> So what I'm asking is: Does anyone have experience with Slony-1 and
>> wide area
>> clusters?
>
> Yes.  My opinion is that it works well for typical cases.
>
> Network failures are a problem for a few reasons:
> 1) It can take Slony a bit to find it's feet again after a network  
> failure.
>   So if you have frequent failures, Slony can get into a situation  
> where
>   it can't get caught back up.
> 2) Slony tends to bomb the slaves with lots of bandwidth when they  
> come
>   back online after an outage.  This can (potentially) be a problem if
>   your bandwidth is limited and it fills up the pipe, interfering with
>   other types of traffic.
> 3) During an outage, Slony has to track all changes until the slave  
> comes
>   back online.  This can use up a lot of disk space pretty quickly, so
>   an extended outage can be a real issue if you don't size your  
> hardware
>   to account for it.
>
> It's a vague question with a vague answer, because whether or not it  
> will
> work for you is a combination of many factors: how much spare  
> bandwidth
> do you have?  How frequent are the outages?  How much updating is  
> occurring?
> How much update lag is acceptable in the slaves during an outage,  
> and how
> much lag to getting caught back up after an outage is acceptable?   
> Can you
> size your disks to be large enough to backlog an outages worth of  
> updates
> while the network is down?
>
> If you can get all those issues into a range that's acceptable for  
> you,
> then Slony will meet your needs, but there are too many questions and
> too many details to be able to provide a pat answer like "yes" or  
> "no".
>
> -- 
> Bill Moran
> Collaborative Fusion Inc.
>
> wmoran at collaborativefusion.com
> Phone: 412-422-3463x4023
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