Hi.
At Fri, 11 Jan 2019 11:36:47 +0900, "Yuzuko Hosoya"
<hosoya.yuz...@lab.ntt.co.jp> wrote in
<000001d4a956$806a2ab0$813e8010$@lab.ntt.co.jp>
> Hi,
>
> Thanks for the comments, and I'm sorry for the late reply.
>
> > From: Tom Lane [mailto:t...@sss.pgh.pa.us]
> > Sent: Friday, January 11, 2019 7:04 AM
> > > Robert Haas <robertmh...@gmail.com> writes:
> > > On Fri, Dec 21, 2018 at 11:50 AM Tom Lane <t...@sss.pgh.pa.us> wrote:
> > >> A smaller-footprint way to fix the immediate problem might be to
> > >> change the values of DEFAULT_INEQ_SEL and friends so that they're
> > >> even less likely to be matched by accident. That is, instead of
> > >> 0.3333333333333333, use 0.333333333333342 or some such.
> >
> > > That's not a dumb idea, but it seems pretty unprincipled to me, and to
> > > be honest I'm kind of surprised that you're not proposing something
> > > cleaner.
> >
> > The problem is the invasiveness of such a change (large) vs the benefit
> > (not so large). The
> upthread
> > patch attempted to add a separate signaling path, but it was very
> > incomplete --- and yet both I
> and
> > Horiguchi-san thought it was already too messy.
> >
> > Maybe at some point we'll go over to something reasonably principled, like
> > adding confidence
> intervals
> > to all selectivity estimates. That would be *really* invasive but perhaps
> > would bring enough
> benefit
> > to justify itself. But the current patch is just attempting to fix one
> > extremely narrow pain
> point,
> > and if that is all it's doing it should have a commensurately small
> > footprint. So I don't think
> the
> > submitted patch looks good from a cost/benefit standpoint.
> >
> Yes, I agree with you. Indeed the patch I attached is insufficient in
> cost-effectiveness.
> However, I want to solve problems of that real estimates happened to equal to
> the default
> values such as this case, even though it's a narrow pain point. So I tried
> distinguishing
> explicitly between real estimates and otherwise as Robert said.
>
> The idea Tom proposed and Horiguchi-san tried seems reasonable, but I'm
> concerned whether
> any range queries really cannot match 0.333333333333342 (or some such) by
> accident in any
> environments. Is the way which Horiguchi-san did enough to prove that?
It cannot be perfect in priciple, but I think it is reliable
enough. This is not principled at all but very effective
comparatively the complexity, I think.
Actually, i/(i*3+1) for some 10^n's are:
1/ 4:binary format: 3f d0 00 00 00 00 00 00
10/ 31:binary format: 3f d4 a5 29 4a 52 94 a5
100/ 301:binary format: 3f d5 43 30 7a 78 c5 51
1000/ 3001:binary format: 3f d5 53 83 74 70 f1 95
10000/ 30001:binary format: 3f d5 55 26 bb 44 2b a8
100000/ 300001:binary format: 3f d5 55 50 ac 4a 74 6d
1000000/ 3000001:binary format: 3f d5 55 54 de 07 5a 96
10000000/ 30000001:binary format: 3f d5 55 55 49 67 22 6d
100000000/ 300000001:binary format: 3f d5 55 55 54 23 e9 d7
1000000000/ 3000000001:binary format: 3f d5 55 55 55 36 ca 95
10000000000/ 30000000001:binary format: 3f d5 55 55 55 52 47 75
100000000000/ 300000000001:binary format: 3f d5 55 55 55 55 07 25
1000000000000/ 3000000000001:binary format: 3f d5 55 55 55 55 4d 84
10000000000000/ 30000000000001:binary format: 3f d5 55 55 55 55 54 8d
100000000000000/ 300000000000001:binary format: 3f d5 55 55 55 55 55 41
1000000000000000/ 3000000000000001:binary format: 3f d5 55 55 55 55 55 53
So, (as Tom said upthread) intuitively we can expect that we are
safe up to roughly 10^10? for the simple cases.
# Of course involving histogram makes things complex, though.
regards.
--
Kyotaro Horiguchi
NTT Open Source Software Center
