[Pgpool-general] Re: Bad degeneration when shutting down secondary backend

[Tatsuo Ishii]

Oops.

replication_stop_on_mismatch = false

was what I wanted to say.
--
Tatsuo Ishii

> Hi Tatsuo, thanks for your response.
> 
> I am already using health check and I have also set
> "replication_stop_on_mismatch = true". The only difference is the pgpool
> version. The problem can be reproduced as follows:
> 
> 1) Setup a pgpool host with two backends in linux boxes with the settings
> explained above.
> 2) Start "stressing" the pgpool host with a constant transaction rate (about
> 4 tps).
> 3) Halt or reboot the secondary backend.
> 
> PS: I know that 2.6.2 is the latest version, but the changelog about the EOF
> error was in the 2.6.1 version
> 
> 
> > -----Original Message-----
> > From: Tatsuo Ishii [mailto:t-ishii at sra.co.jp] 
> > Sent: Domingo, 14 de Agosto de 2005 09:10 a.m.
> > To: Pablo G. Milano
> > Cc: pgpool-general at pgfoundry.org
> > Subject: Re: Bad degeneration when shutting down secondary backend
> > 
> > > I am using pgpool 2.5.1 with linux kernel 2.6.8
> > > 
> > > I noticed this repeteable behaviour in a heavily loaded environment:
> > > When shutting down the linux box containing the backend 
> > configured as
> > > "secondary", while sending transactions to pgpool, 
> > degeneration mode shuts
> > > down primary backend instead of secondary. The log shows 
> > the following:
> > > 
> > > ---------------------------------------
> > > Aug 12 15:04:14 asimov pgpool: 2005-08-12 15:04:14 ERROR: pid 5888:
> > > pool_process_query: kind does not match between backends master(C)
> > > secondary(E)
> > > Aug 12 15:04:14 asimov pgpool: 2005-08-12 15:04:14 LOG:   pid 5888:
> > > notice_backend_error: master: 1 fail over request from pid 5888
> > > Aug 12 15:04:14 asimov pgpool: 2005-08-12 15:04:14 LOG:   
> > pid 5876: starting
> > > degeneration. shutdown master host asimov(5432)
> > > Aug 12 15:04:15 asimov pgpool: 2005-08-12 15:04:15 LOG:   pid 5876:
> > > degeneration done. shutdown master host asimov(5432)
> > > ---------------------------------------
> > > 
> > > It seems that pgpool encounters a data mismatch between 
> > backends, when what
> > > really happens is that one of them is dying.
> > > I've found this in pgpool 2.6.1 changelog:
> > > 
> > > 	* do not raise failover when read() read encounters 
> > EOF. It seems it
> > > 	  is a oversight. Backend crush may cause that but it does not
> > > 	  immediately mean postmaster crush
> > > 
> > > Does this solve the problem I'm having? Should I move to 
> > pgpool 2.6.1?
> > > Thanks in advance.
> > 
> > Maybe.
> > 
> > But for particular error like this:
> > 
> > > pool_process_query: kind does not match between backends master(C)
> > > secondary(E)
> > 
> > I don't think upgrading to 2.6.2(the latest version is 2.6.2, not
> > 2.6.21, FYI) solves the problem. The query results do not agree
> > between two servers. pgpool cannot judge which one is healthy. So it
> > just shuts down the master. 
> > 
> > What I would sugget here is:
> > 
> > 1) set following in pgpoo.conf. This will avoid unwanted degeneration.
> > 
> >    replication_stop_on_mismatch = true
> > 
> > 2) upgrade to 2.6.2. and use "health check" functionality. Heal check
> >    will occasionally checks if the servers are healthy and if
> >    something goes wrong, automatically starts the degeneration.
> > --
> > Tatsuo Ishii
> > 
>