[Pgpool-general] can't attach two nodes simultaneously

[Tomasz Chmielewski]

Am 15.04.2010 06:34, Tatsuo Ishii wrote:

>> 2. Is there a way to attach multiple nodes in an "atomic" way?
> 
> Why do you need atomicity for this?

Because only then it is guaranteed that the databases will be in sync.

Consider this:

1. pgpool with 2 backends
2. 2 backends are detached for some reason (i.e. switch/cabling changes, pgpool sitting on a different host than the databases)
3. clients are trying to write to pgpool continuously
4. switch/cabling repaired
5. you do "pcp_attach_node ... 0" to attach node 0
6. there are some writes happening which go to node 0 only
7. yo do "pcp_attach_node ... 0" to attach node 1
8. writes go to both nodes now, but node 1 does not contain some data now


There is a workaround: stop pgpool, remove its status file, start it again, but that's not really it.


-- 
Tomasz Chmielewski
http://wpkg.org