Re: Fsync request queue

On Tue, May 1, 2018 at 1:41 PM, Andres Freund <andres@anarazel.de> wrote:
> 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.

Hmm.  Partitioning probably does make it easier to overrun the queue,
but even so it seems hard -- the queue has one entry per shared
buffer, which is a lot.

-- 
Robert Haas
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