On Thu, Jun 25, 2020 at 2:11 PM David Steele <[email protected]> wrote:
> On 6/24/20 6:27 PM, Tom Lane wrote: > > David Steele <[email protected]> writes: > >> ... So apparently it is possible. To get them working as soon as > possible I > >> recommended that they run: > >> alter role postgres set max_parallel_workers_per_gather = 0; > >> And that solved their problem. 9.6 is getting on in years so I'm not > >> sure how much time/effort we want to spend on this, but I figured it was > >> worth mentioning. > > > >> I did another round of trying to reproduce the issue but came up short a > >> second time. > > > > I was able to force it like this: > > > > regression=# set force_parallel_mode TO 'on'; > > SET > > Ah, yes, that works. Now at least I can test it. > > > It doesn't seem terribly likely that anybody would be using > > force_parallel_mode = on in production, but perhaps there's some > > reasonable combination of the other parallelization planning GUCs > > that can make this plan look attractive. > > I'll also ask the user if they have this GUC enabled. > Maybe have pgbackrest issue an explicit SET force_parallel_mode=off when it runs against a 9.6? > I'm kind of inclined not to bother with a code fix at this late date, > > given that we've had so few trouble reports. The right answer is > > to tell anyone who's affected to fix their catalogs manually, viz > > > > update pg_proc set proparallel = 'r' where proname = 'pg_start_backup'; > > update pg_proc set proparallel = 'r' where proname = 'pg_stop_backup'; > > Only pg_stop_backup() needs to be updated, but that's probably the best > solution. > > > If we had back-patched 9fe3c644a (sans catversion bump of course) > > at the time, then initdb's done with 9.6.3 or later would have gotten > > this right. In hindsight, not doing that was clearly wrong. But it > > seems a bit late to do it now. > > OK by me. > +1. Seems infrequent enough or we would've heard much about it before. And it's not going to be *all* that common with brand new clusters on 9.6 these days (I hope). -- Magnus Hagander Me: https://www.hagander.net/ <http://www.hagander.net/> Work: https://www.redpill-linpro.com/ <http://www.redpill-linpro.com/>
