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.

---------------------------------------------------------------------------

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
>
> ---------------------------(end of broadcast)---------------------------
> TIP 2: Don't 'kill -9' the postmaster

--
Bruce Momjian bruce(at)momjian(dot)us
EnterpriseDB http://www.enterprisedb.com

+ If your life is a hard drive, Christ can be your backup. +