Re: vacuumdb parallel has a deadlock detected in 9.5.4

hubert depesz lubaczewski wrote:
> On Wed, Sep 28, 2016 at 09:46:22PM +0800, huang wrote:
> >  Hi friends,
> >
> > There is a error deadlock detected in vacuumdb parallel .
> > but if I do not use parallel , it has not deadlock detected .
>
> man vacuumdb says about -j option:
>
> >> Note that using this mode together with the -f (FULL) option might cause
> >> deadlock failures if certain system catalogs are processed in parallel.
>
> so, while I understand it's not pretty, it's well documented.

Yeah.  However I think this behavior is rather unhelpful.  Maybe we
should try to fix it somehow, but I'm not sure how.  We could say that
pg_catalog tables can only be processed one at a time, instead of trying
to paralelize them?  For example: have vacuumdb fill two lists of
tables, one for pg_catalog and one for tables in other schemas.  Each
worker chooses a table from the pg_catalog list first if it's not empty
and there's no other worker doing one of these, otherwise one from the
other table.

I think that'd fix it, while not destroying paralelizability too badly.

I'm not volunteering, though.  Patches welcome.

--
Álvaro Herrera                https://www.2ndQuadrant.com/
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