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

[Tatsuo Ishii]

> > 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.
> Would not it be a good behavior to degenerate the backends that return a
> query error while the master do not?

Currently pgpool-II just detects number of affected raws by
INSERT/UPDATE/DELETE and reports errors. Next verion of pgpool-II will
allow user to choose degeneration in this case or not in addition to
reporting errors.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp

> I am concerned because I have an environment with seven backends in
> load_balance_mode and it seems I can not be sure of the data integrity
> of these backends in this mode.
> 
> - -Ramon
> 
> 
> > 
> >> 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
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