Re: [RFC PATCH] index-pack: improve performance on NFS

On Sat, Nov 10, 2018 at 03:04:35PM +0100, Ævar Arnfjörð Bjarmason wrote:

d) As shown in the linked E-Mails of mine you sometimes pay a 2-3 second
   *fixed* cost even for a very small (think ~100-200 objects) push/fetch
   that would otherwise take milliseconds with Jeff's version of this
   optimization (and not with mine). This can be a hundred/thousands of
   percent slowdown.

   Is that a big deal in itself in terms of absolute time spent? No. But
   I'm also thinking about this from the perspective of getting noise
   out of performance metrics. Some of this slowdown is also "user
   waiting for the terminal to be usable again" not just some machine
   somewhere wasting its own time.

IMHO the ultimate end-game in this direction is still "don't have a
bunch of loose objects".

Right now this can legitimately happen due to unreachable-but-recent
objects being exploded out (or never packed in the first place). But I
hope in the long run that we'll actually put these into packs. That will
make this case faster _and_ avoid extra work during gc _and_ fix the
"whoops, we just ran gc but you still have a lot of objects" problem.

Which doesn't invalidate your other four points, of course. ;)

-Peff