[pgpool-general: 9058] Re: 0 th backend is not valid after upgrading to 4.5.1

[Emond Papegaaij]

Op za 30 mrt 2024 om 08:42 schreef Tatsuo Ishii <ishii at sraoss.co.jp>:

> > Op vr 29 mrt 2024 om 15:26 schreef Tatsuo Ishii <ishii at sraoss.co.jp>:
> >
> >> > Hi,
> >> >
> >> > After upgrading from 4.5.0 to 4.5.1 we see lots of regressions in our
> >> > test-suite when failovers are involved with the following exception in
> >> > WildFly:
> >> > Caused by: org.postgresql.util.PSQLException: ERROR: unable to read
> >> message
> >> > kind from backend
> >> >   Detail: 0 th backend is not valid
> >> >
> Ok. The commit you pointed out:
> > is the change that is causing the problems:
> >
> https://github.com/pgpool/pgpool2/commit/a2a86804cb838b416f317cc083d521a5c691f2ec
>
> has a bug: when load_balance_mode is off, I found that it does not
> work unless the primary node id is 0. It should have set
> query_context->where_to_send map for the primary node id but when the
> primary node id is not 0, the map was not set at all. This makes
> Pgpool-II believe that 0 th backend needs to be accessed. This lead to
> the error you are seeing.  Another error case I found was
> (incorrectly) reading from node 0, which leads to hang up. This is
> easy to reproduce.
>
> (1) create a two-node cluster using pgpool_setup
>
> (2) shutdown node 0 and recover node 1 (pcp_recovery_node 0). This
> makes node 0 to be standby, node 1 to be primary.
>
> (3) add followings to pgpool.conf and restart whole cluster.
>
> load_balance_mode = off
> backend_weight1 = 0
>
> (4) type "begin" from psql. It gets stuck.
>
> Attached is the patch against 4.5.1.
>

Thanks for the quick fix! I've applied the patch and rescheduled a build.
However, this will take some time and Easter is a national holiday in the
Netherlands, so I probably won't be able to report back until Tuesday.

Best regards,
Emond
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