Re: [HACKERS] Proposal for a cascaded master-slave replication system

Jan,

This is EXACTLY what we have been waiting for (years) :) :) :).
If you need somebody for testing or documentation just drop me a line.

	Cheers,

		Hans



Jan Wieck wrote:
> Hans-Jürgen Schönig wrote:
> 
>> Jan,
>>
>> First of all we really appreciate that this is going to be an Open 
>> Source project.
>> There is something I wanted to add from a marketing point of view: I 
>> have done many public talks in the 2 years or so. There is one 
>> question people keep asking me: "How about the pgreplication 
>> project?". In every training course, at any conference people keep 
>> asking for synchronous replication. We have offered this people some 
>> async solutions which are already out there but nobody seems to be 
>> interested in having it (my person impression). People keep asking for 
>> a sync approach via email but nobody seems to care about an async 
>> approach. This does not mean that async is bad but we can see a strong 
>> demand for synchronous replication.
>>
>> Meanwhile we seem to be in a situation where PostgreSQL is rather 
>> competing against Oracle than against MySQL. In our case there are 
>> more people asking for Oracle -> Pg migration than for MySQL -> Pg. 
>> MySQL does not seem to be the great enemy because most people know 
>> that it is an inferior product anyway. What I want to point out is 
>> that some people want an alternative Oracle's Real Application 
>> Cluster. They want load balancing and hot failover. Even data centers 
>> asking for replication did not want to have an async approach in the 
>> past.
> 
> 
> Hans-Jürgen,
> 
> we are well aware of the high demand for multi-master replication 
> addressing load balancing and clustering. We have that need ourself as 
> well and I plan to work on a follow-up project as soon as Slony-I is 
> released. But as of now, we see a higher priority for a reliable master 
> slave system that includes the cascading and backup features described 
> in my concept. There are a couple of different similar product out 
> there, I know. But show me one of them where you can failover without 
> becoming the single point of failure? We've just recently seen ... or 
> better "where not able to see anything any more" how failures tend to 
> ripple through systems - half of the US East Coast was dark. So where is 
> the replication system where a slave becomes the "master", and not a 
> standalone server. Show me one that has a clear concept of failback, one 
> that has hot-join as a primary design goal. These are the features that 
> I expect if something is labeled "Enterprise Level".
> 
> As far as my ideas for multi-master go, it will be a synchronous 
> solution using group communication. My idea is "group commit" instead of 
> 2-Phase ... and an early stage test hack has replicated some update 3 
> weeks ago. The big challange will be to integrate the two systems so 
> that a node can start as an asynchronous Slony-I slave, catch up ... and 
> switch over to synchronous multimaster without stopping the cluster. I 
> have no clue yet how to do that, but I refuse to think smaller.
> 
> 
> Jan
> 


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