Hi Greg, On Sunday, September 25, 2011 03:25:50 AM Greg Stark wrote: > On Sat, Sep 24, 2011 at 4:16 PM, Magnus Hagander <mag...@hagander.net> wrote: > > I was assuming the kernel was smart enough to read this as "*this* > > process is not going to be using this file anymore", not "nobody in > > the whole machine is going to use this file anymore". And the process > > running the base backup is certainly not going to read it again. > > > > But that's a good point - do you know if that is the case, or does it > > mandate more testing? > It's not the case on Linux. I used to use DONTNEED to flush pages from > cache before running a benchmark. I verified with mincore that the > pages were actually getting removed from cache. Sometimes there was > the occasional straggler but nearly all got flushed and after a second > or third pass the stragglers were gone too. Not sure what exactly is "not the case on Linux". Your answer could be read in a way that the fadvise/DONTNEED adheres to some sort of refcounting scheme (which it afaik does not) or that it doesn't.
> In case you're wondering, this was because using /proc/.../drop_caches > caused flaky benchmarks. My theory was that it was causing pages of > the executable to trigger page faults in the middle of the benchmark. That should be easily possible to rule out by preloading the applications+libraries? I think there were plans to teach the dynamic linker to enforce doing so, but I am not sure they were ever folloowed through. Andres -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
