[pgpool-general: 2725] Re: Using one pgpoll instance per app server?

[Tatsuo Ishii]

>> More serious problem is, it is possible that on a flaky network
>> (switch) pgpool1 detects Master DB goes down because of connection
>> problem between pgpool1 and Master DB (actually Master DB does not go
>> down), and promotes Slave DB to master. On the other hand, connection
>> between pgpool2 and Master DB is healthy and pgpool2 keeps on sending
>> update requests to Master DB. As a result, both Master DB and Slave
>> DB are now indecent master DB (we call it "split brain").
>> 
>> This kind of problem can be solved by watchdog: all watchdog process on
>> pgpool[123] communicates each other to solve the problem described
>> above. In the connection problem scenario between pgpool1 and Master
>> DB, pgpool1 initiates failover, then let pgpool2 and pgpool3 recognize
>> Master DB goes down.
> 
> Do you know if there has been a tutorial or if there exists some
> documentation, which describes the proper setup of watchdog for this
> kind of scenario? Any hint or link would be much appreciated.

As far as I know, there's none. Let me think to write a document...

>> > Now imagine that replication between master and slave DB is handled by
>> > those pgpool instances as well. Would this still be possible?
>> 
>> What do you mean by "handled"? You mean pgpool's native replication
>> (without using streaming replication of PostgreSQL)?
> 
> Yes, that's what I meant. Using pgpool's native replication. Is that
> possible in this sort of setup?

Yes, of course.

Best regards,
--
Tatsuo Ishii
SRA OSS, Inc. Japan
English: http://www.sraoss.co.jp/index_en.php
Japanese: http://www.sraoss.co.jp