On 2018-05-01 13:21:21 -0400, Robert Haas wrote:
> On Mon, Apr 30, 2018 at 7:08 PM, Andres Freund <andres@anarazel.de> wrote:
> >> True, but has anyone ever actually observed a non-zero
> >> pg_stat_bgwriter.buffers_backend_fsync in the wild after the
> >> compaction queue stuff was added/backpatched?
> >
> > Yes.
>
> Care to elaborate?
I unfortunately don't have access to the relevant reports anymore, so
it's only by memory. What I do remember is that a few I saw
pg_stat_bgwriter.buffers_backend_fsync values that we a pretty sizable
fraction of the buffers written by backends. I don't think I ever
figured out how problematic that was from a peformance perspective, and
how large a fraction of the overall number of fsyncs those were.
One was a workload with citus (lots of tables per node), and one was
inheritance based partitioning. There were a few others too, where I
don't recall anything about the workload.
Greetings,
Andres Freund