On Sat, Nov 12, 2016 at 4:03 AM, Amit Kapila <amit.kapil...@gmail.com> wrote:
> On Fri, Nov 11, 2016 at 3:01 PM, Magnus Hagander <mag...@hagander.net> > wrote: > >> > Based on this optimization we might want to keep the text that says > >> > large > >> > shared buffers on Windows aren't as effective perhaps, > > Sounds sensible or may add a line to say why it isn't as effective as on > Linux. > Do we actually know *why*? > > and just remove > >> > the > >> > sentence that explicitly says don't go over 512MB? > >> > > Have we done any windows specific optimization since it was originally > mentioned as 512MB which indicates that we can remove it? Are you > telling it based on results in this thread, if so, I think it is > better to do few more tests before changing it. > Well, that advice goes *way* back. Many things have changed since then - and just look at things like the updating of the stats target. For one thing, we're in 64-bit now, not 32, for the majority of users. We reserve the shared memory on startup which was done for address probability issues, but may have had side effects. And *Windows itself* has changed in those 10 or so years. I've heard it from other people as well, but this thread is definitely one of them. I think the old truth about "never go above that" is invalid at this point, but it may never have been valid. But I also don't think we know what to put there instead, as a recommendation. > >> Just removing the reference to the size would make users ask a question > >> "What size is the effective upper limit?" > > > > > > True, but that's a question for other platforms as well, isn't it? > > > > Right, but for other platforms, the recommendation seems to be 25% of > RAM, can we safely say that for Windows as well? As per test results > in this thread, it seems the read-write performance degrades when > shared buffers have increased from 12.5 to 25%. I think as the test > is done for a short duration so that degradation could be just a run > to run to run variation, that's why I suggested doing few more tests. We talk about 25%, but only up to a certain size. It's suggested as a starting point. The 25% value us probably good as a starting point, as it's recommended, but not as a "recommended setting". I'm fine with doing something similar for Windows -- say "10-15% as a starting point, but you have to check with your workload" kind of statements. -- Magnus Hagander Me: http://www.hagander.net/ Work: http://www.redpill-linpro.com/