Re: [PATCHES] replication docs: split single vs.

I have renamed the documentation section "High Availability and Load
Balancing".  I think the current version takes many of your comments
below into account.  Please let me know.

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Markus Schiltknecht wrote:
> Good morning Hannu,
> 
> Hannu Krosing wrote:
> > People do that in cases where there is high write loads ("high" as in
> > "not 10+ times less than reads") and just replicating the RO copies
> > would be prohibitively expensive in either network, cpu or memory terms.
> 
> Okay. It that case it's even less like any type of replication.
> 
> IMO, Data Partitioning is the most simple method of Load Balancing. It's 
> like saying: hey, if your database server is overloaded, simply split 
> your data over multiple servers.
> 
> Which is not always possible and can lead to other problems. Some of 
> which can solved by replication solutions.
> 
> > In what way is pgpool multimaster ? last time I looked it did nothing
> > but applying DML to several databses. i.e. it is not replication at all,
> 
> Please give your definition of replication.
> 
> Wikipedia gives us [1]: "Replication refers to the use of redundant 
> resources, such as software or hardware components, to improve 
> reliability, fault-tolerance, or performance."
> 
> Pgpool does that by Query Broadcasting, no?
> 
> > or at least it is masterless, unless we think of the pgpool process
> > itself as the _single_ master :)
> 
> Hm. That's a good point. Pgpool allows to write to only one master (the 
> pgpool process) but read from multiple, synchronous masters. I admit 
> that makes it a little hard to split into Single- or Multi-Master.
> 
> Doesn't Sequoia support multiple Query Broadcasting processes? Would it 
> qualify as Multi-Master *Replication*, then?
> 
> In an ideal implementation, every Master could broadcast queries to all 
> other masters. Thus giving a *real* Multi-Master solution. Postgres-R 
> (6.4) did fall back into that mode for transactions which change a lot 
> of tuples, so that the writeset didn't exceed a certain size limit.
> 
> > I think this gives completely wrong picture of what pgpool does.
> 
> As I see it, that's because pgpool is a very limited implementation of 
> Query Broadcasting. But pgpool is not the only solution implementing 
> that algorithm. Do we want to describe the general algorithm or pgpool here?
> 
> Regards
> 
> Markus
> 
> 
> [1]: Wikipedia about Replication (Computer Science):
> http://en.wikipedia.org/wiki/Replication_%28computer_science%29
> 
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