Re: Perf Benchmarking and regression.

On 2016-06-03 12:31:58 -0400, Robert Haas wrote:
> Now, what varies IME is how much total RAM there is in the system and
> how frequently they write that data, as opposed to reading it. If
> they are on a tightly RAM-constrained system, then this situation
> won't arise because they won't be under the dirty background limit.
> And if they aren't writing that much data then they'll be fine too.
> But even putting all of that together I really don't see why you're
> trying to suggest that this is some bizarre set of circumstances that
> should only rarely happen in the real world.

I'm saying that if that happens constantly, you're better off adjusting
shared_buffers, because you're likely already suffering from latency
spikes and other issues. Optimizing for massive random write throughput
in a system that's not configured appropriately, at the cost of well
configured systems to suffer, doesn't seem like a good tradeoff to me.

Note that other operating systems like windows and freebsd *alreaddy*
write back much more aggressively (independent of this change). I seem
to recall you yourself being quite passionately arguing that the linux
behaviour around this is broken.

Greetings,

Andres Freund