[Pgpool-general] Basics of replication with pgpool-II - how does it work? compared to Slony? to Postgres log shipping?

[Tatsuo Ishii]

Thanks for the suggestion, Aleksey. I'm not very good at writing
English, so if someone come up with addition to the doc, I will
appreciate.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

> Dear Tatsuo,
> 
>   Thanks, that's a great explanation, very clear.
> 
>   Maybe you could add it to the pgpool-II manual, in the
> Replication section?  Just a suggestion.
> 
> Thank you!
> Aleksey
> 
> 
> On Mon, Jun 7, 2010 at 6:00 PM, Tatsuo Ishii <ishii at sraoss.co.jp> wrote:
> >> Hi.   We want to have redundancy for our database;
> >> is pgpool-II the right tool, with it's replication mode?
> >>
> >> We want to have 2 database servers, and if one
> >> dies, our application just goes on using the other
> >> one, while we repair the broken one.
> >>
> >> Can pgpool-II replicate writes such that if a write
> >> query is submitted, pgpool-II will write it to DB server
> >> A and DB server B, and will only return a success
> >> to the client if both writes succeeded?  otherwise
> >> it will return a failure, perform any necessary rollback
> >> if the write was replicated only to one server?
> >
> > Yes, pgpool-II exactly works as you described. Plus, with write query
> > pgpool-II start a transaction if it's not already started by user.
> > The write order is first A then B (if A is the first one on
> > pgpool.conf). Commit order is B then A.
> >
> >  If write query fails, pgpool-II aborts the transaction and start
> > a  degenration, which will be seen as connection shutdown from
> > PostgreSQL server by client. By reconnecting pgpool-II, client can use
> > the healthy PostgreSQL.
> >
> > Please note that "fail" does not mean here a query error (for example,
> > violation of constraints). Rather "fail" means network error or
> > PostgreSQL server down or some such.
> >
> >> If that's not how pgpool-II replication works, how does
> >> it work?  I've looked at the manual but I still don't
> >> understand.
> >>
> >> I'm familiar with replication with Postgres 8 log shipping
> >> (warm standby),  Postgres 9 streaming replication
> >> (hot standby), and Slony (hot standby).  How does
> >> Pgpool-II replication work and how does it compare to
> >> the Postgres/Slony replication?
> >
> > They are all log(physical or logical one) based asynchronous
> > replication systems. Pgpool-II is a query based synchronous
> > replication.  That's the big difference. In addition, those
> > replication systems do not have any automatic failover/load balancing
> > functionality while pgpool-II has.
> > --
> > Tatsuo Ishii
> > SRA OSS, Inc. Japan
> > English: http://www.sraoss.co.jp/index_en.php
> > Japanese: http://www.sraoss.co.jp
> >
> _______________________________________________
> Pgpool-general mailing list
> Pgpool-general at pgfoundry.org
> http://pgfoundry.org/mailman/listinfo/pgpool-general