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 <[email protected]> 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 [email protected] http://pgfoundry.org/mailman/listinfo/pgpool-general
