Re: BUG #13643: Should a process dying bring postgresql down, or not?

amir(dot)rohan(at)mail(dot)com wrote:

> postgres 2181 0.0 0.1 134468 9504 pts/0 T 03:34 0:00 /usr/local/pgsql/bin/postgres -D /home/local/pg/s1
> postgres 2183 0.0 0.0 134576 4168 ? Ss 03:34 0:00 postgres: checkpointer process
> postgres 2184 0.0 0.0 134604 2844 ? Ss 03:34 0:00 postgres: writer process
> postgres 2185 0.0 0.0 134468 2780 ? Ss 03:34 0:00 postgres: wal writer process
> postgres 2186 0.0 0.0 0 0 ? Zs 03:34 0:00 [postgres] <defunct> <<<<<<<<<<<<<<< dead process
> postgres 2187 0.0 0.0 127300 2204 ? Ss 03:34 0:00 postgres: stats collector process
> postgres 2193 0.0 0.0 118164 2696 pts/0 T 03:34 0:00 pg_basebackup -D /home/local/pg/backup -p 57833 --format=t -x
> postgres 2194 0.0 0.0 134916 6016 ? Ss 03:34 0:00 postgres: wal sender process user1 [local] sending backup "pg_basebackup base backup"
>
> Not sure if this is a real problem or not, but it was my understanding that
> pg panics when a subprocess dies for safety resons.

A zombie process is a process that died and hasn't been collected by its
parent process. In this case, postmaster is stopped ("T" above), so it
cannot call wait() to collect the dead process. Once you signal
postmaster to run again, it will either discover that the process died
cleanly (and clean up state and all is well), or that it died uncleanly
(in which case it will cause all other processes to stop).

That postmaster is in STOPped mode is the issue here. That doesn't
happen unless you take specific action to do that.

--
Álvaro Herrera http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services