Re: High Availability, Load Balancing, and Replication Feature Matrix

Markus Schiltknecht wrote:
> Hello Bruce,
>
> Bruce Momjian wrote:
> > Uh, I think of PgCluster as multi-master, but in a way it is a hybrid
> > because there is a central server that gets all the queries.
>
> Yes, PgCluster as well as Sequoia use statement based replication.
> Sequoia is also clearly a middleware (no changes to Postgres needed).
>
> Both suffer from the limitations you describe in "statement based
> replication middleware". AFAICT Sequoia does quite well in circumventing
> those. (Heck, it even tries to masquerade differences between database
> systems, so you can keep a Postgres database in sync with a MySQL one.)
>
> Depending on the RAIDb level you are using, Sequoia can be considered
> multi-master (RAIDb-1) or single-master (RAIDb-0). Also note that
> sequoia can run multiple controllers, thus it does not rely on one
> central server.

But in those cases isn't the multi-master just at the storage level?  I
don't consider that multi-"master".

> So, at least Sequoia is clearly a hybrid, in between your definitions of
> "statement based replication middleware" and "synchronous multi-master
> replication". Depending on how "middleware" you consider PgCluster, it's
> also a hybrid. Certainly it does statement based replication.

I am afraid we are stuck between clarity and understand-ability here. ;-)

--
  Bruce Momjian  <bruce@momjian.us>        http://momjian.us
  EnterpriseDB                             http://postgres.enterprisedb.com

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