Re: Horrible CREATE DATABASE Performance in High Sierra

Tom, Andres -

Is there an issue tracker I could be looking at to follow along on the
progress on this issue?

Thanks so much!

On Mon, Oct 2, 2017 at 9:06 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:

> Andres Freund <andres(at)anarazel(dot)de> writes:
> > On 2017-10-02 19:50:51 -0400, Tom Lane wrote:
> >> What I saw was that the backend process was consuming 100% of (one) CPU,
> >> while the I/O transaction rate viewed by "iostat 1" started pretty low
> >> --- under 10% of what the machine is capable of --- and dropped from
> >> there as the copy proceeded. I did not think to check if that was user
> >> or kernel-space CPU, but I imagine it has to be the latter.
>
> > So that's pretty clearly a kernel bug... Hm. I wonder if it's mmap() or
> > msync() that's the problem here. I guess you didn't run a profile?
>
> Interestingly, profiling with Activity Monitor seems to blame the problem
> entirely on munmap() ... which squares with the place I hit every time
> when randomly stopping the process with gdb^Hlldb, so I'm inclined to
> believe it.
>
> This still offers no insight as to why CREATE DATABASE is hitting the
> problem while regular flush activity doesn't.
>
> > One interesting thing here is that in the CREATE DATABASE case there'll
> > probably be a lot larger contiguous mappings than in *_flush_after
> > cases. So it might be related to the size of the mapping / flush "unit".
>
> Meh, the mapping is only 64K in this case vs. 8K in the other. Hard
> to credit that it breaks that easily.
>
> regards, tom lane
>