Re: [BUGS] BUG #14155: bloom index error with unlogged table

"David G. Johnston" <david.g.johnston@gmail.com> writes:
> On Tue, Jun 7, 2016 at 1:35 AM, Michael Paquier <michael.paquier@gmail.com>
> wrote:
>> I have finally given a shot at improving the docs with the attached.
>> Comments are welcome.

> [ assorted comments ]

I adopted most of David's suggestions, whacked it around a bit further
myself, and committed.  See what you think.

> ​It would be nice to give guidance on selecting a bit size for columns and
> a signature length​.  Yes, Wikipedia covers the topic but to get the reader
> started some discussion of the relevant trade-offs when using larger
> numbers than the default would be nice.  I don't suspect using smaller the
> default values is apt to be worthwhile...

Agreed, but I didn't want to write such text myself.  There's room for
further improvement here.  I did add a note in the main example about
what happens with a non-default signature length, but that hardly
constitutes guidance.

BTW, it seemed to me while generating the example that the planner's
costing for bloom index searches was unduly pessimistic; maybe there's
work to do there?
        regards, tom lane