Re: Typos/Questions in bloom documentation

On Wed, Apr 20, 2016 at 9:18 PM, Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp
> wrote:

> On 2016/04/21 11:19, David G. Johnston wrote:
> > On Wednesday, April 20, 2016, Amit Langote wrote:
> >> On 2016/04/21 6:51, David G. Johnston wrote:
> >>> http://www.postgresql.org/docs/devel/static/bloom.html
> >>>
> >>> F.4.3 Examples
> >>>
> >>> Claims that the signature length is 80 bits - shouldn't it be 8?
> >>
> >> In F.4.1. Introduction:
> >>
> >> ... The user can specify signature length (in uint16, default is 5)
> >>
> >> So, it seems right to me.
> >>
> > Great. Maybe you can consider re-wording it so others can understand. I
> > have no clue how 80bits is determined. The phase you quote is obtuse to
> > the casual user as well. If that means 16x5=80 irrespective of columns
> it
> > is not clear.
>
> I agree it's unclear. Does the following make it any better (updated
> patch attached):
>
> - The user can specify signature length (in uint16, default is 5) and the
> - number of bits, which can be set per attribute (1 < colN < 2048).
> + The user can specify signature length in units of 16 bits (default is
> 5)
> + and the number of bits per indexed attribute.
>
>
​Better. The "and" is confusing. Is the signature length the sum of 16x5
+ (bits per indexed attribute)​?

By the way, now I am slightly confused as well about per-column bits
> assignment thing:
>
> In F.4.1. Introduction:
>
> ... and the number of bits, which can be set per attribute (1 < colN <
> 2048).
>
> And then in F.4.2. Parameters:
>
> bloom indexes accept the following parameters in the WITH clause.
>
> length
> Length of signature in uint16 type values
>

How about: "Number of 16bit units to use for the signature"

> col1 — col16
> Number of bits for corresponding column
>
> Which is it: col1 - col2048 or col1 - col16? Or are they different things
> altogether?
>

​Good question...

David J.​