> Sorry for sending lots of messages. When does the data get replicated? > For example, if I perform a write (Insert operation), does it get > copied over to all other nodes at the same moment?
"same moment" is impossible by relativity theory:-) pgpool waits until all writes on nodes be finished. Note that readers could, for example, read before node 2 is written but after node 1 is written. If you want to let readers wait until all the nodes be written, you could use table locking with writer but it will lead to bad things as I already suggested. I guess another related question is what is pgpool doing to maintain data consistency. There are simple rules: 1) Always send queries to all the nodes if it's a write query 2) Detach a node if it fails. 3) Always execute queries in a transaction. If a node fails, the transaction aborts to rollback to previous data. -- Tatsuo Ishii SRA OSS, Inc. Japan > Thanks, > Harold > > > --- On Wed, 4/8/09, Tatsuo Ishii <[email protected]> wrote: > > > From: Tatsuo Ishii <[email protected]> > > Subject: Re: [Pgpool-general] pgpool-II documentation > > To: [email protected] > > Cc: [email protected] > > Date: Wednesday, April 8, 2009, 9:03 PM > > > Hi All, > > > > > > Is there a more in-depth documentation of pgpool? > > > > Before stepping into pgpool internal, it' s best to > > understand how > > PostgreSQL frontend/backend protocol works. See > > "Frontend/Backend > > Protocol". > > > > > I'm mostly interested in how pgpool does the > > replication process (how it ensures consistency, especially > > under load_balance_mode). > > > > There are some explanation in the pgpool-II docs(the latest > > one > > is:http://pgpool.projects.postgresql.org/pgpool-II/doc/pgpool-en.html). > > > > > > Look into around: > > http://pgpool.projects.postgresql.org/pgpool-II/doc/pgpool-en.html#config > > ------------------------------------------------------------------- > > replicate_select > > > > When set to true, pgpool-II replicate SELECTs. If > > false, pgpool-II > > only sends them to Master DB. Default is false. > > ------------------------------------------------------------------- > > > > and: > > > > http://pgpool.projects.postgresql.org/pgpool-II/doc/load_balance.png > > > > Also I'm going to give a talk at PGCon 2009 in Ottawa. > > I would like to > > talk about how pgpool-II tries to keep the consistency > > among databases. > > -- > > Tatsuo Ishii > > SRA OSS, Inc. Japan _______________________________________________ Pgpool-general mailing list [email protected] http://pgfoundry.org/mailman/listinfo/pgpool-general
