Re: Regression tests fail on OpenBSD due to low semmns value

Alexander Lakhin <exclusion(at)gmail(dot)com> writes:
> I deployed OpenBSD 7.4 locally and reproduced "too many clients" and that
> hang as well. It turned out that OpenBSD has semmns as low as 60 (see [4])
> and as a consequence, initdb sets max_connections = 20 for the regression
> test database. (This can be helpful sometimes, see e.g., [5].) At the same
> time, paralell_schedule contains groups of 20 tests, for instance:

Yeah. That was more-or-less okay before we invented parallel query,
but now there needs to be some headroom. I've thought about adjusting
initdb to not allow max_connections less than 25 (can't remember if
I actually proposed that on-list though). The other way would be to
rearrange parallel_schedule to make the max group size less than 20,
but that seems like a lot of effort for little benefit.

FTR, NetBSD also has unreasonably tiny semaphore settings out-of-the
box. mamba's host is using

kern.ipc.semmni=100
kern.ipc.semmns=1000

and for that matter

kern.maxvnodes=60000
kern.maxproc=1000
kern.maxfiles=10000

> ...
> So GetSafeSnapshot() waits indefinitely for possibleUnsafeConflicts to
> become empty (for other backend to remove itself from the list of possible conflicts
> inside ReleasePredicateLocks()), but it doesn't happen.

This seems like an actual bug?

regards, tom lane