Horton

Re: crashes due to setting max_parallel_workers=0

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Rushabh Lathia <rushabh.lathia@gmail.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, David Rowley <david.rowley@2ndquadrant.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2017-04-01T01:22:14Z
Lists: pgsql-hackers 
On Tue, Mar 28, 2017 at 11:08 PM, Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
> Maybe. It depends on how valuable it's to keep Gather and GatherMerge
> similar - having nreaders in one and not the other seems a bit weird. But
> maybe the refactoring would remove it from both nodes?

Yeah, it appears to be the case that both Gather and GatherMerge
inevitably end up with nworkers_launched == nreaders, which seems
dumb.  If we're going to clean this up, I think we should  make them
both match.

> Also, it does not really solve the issue that we're using 'nreaders' or
> 'nworkers_launched' to access array with one extra element.

I'm not clear that there's any fundamental solution to that problem
other than trying to clarify it through comments.

Meantime, I think it's not good to leave this crashing, so I pushed
Rushabh's v2 patch for the actual crash for now.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

Commits

  1. Avoid GatherMerge crash when there are no workers.