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