Re: Comment in ginpostinglist.c doesn't match code

On Fri, Aug 23, 2019 at 7:05 AM Ashwin Agrawal <aagrawal@pivotal.io> wrote:
>
> On Thu, Aug 22, 2019 at 1:14 AM Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>>
>>
>> The patch also includes a little unit test module to test this without
>> creating a 16 TB table. A whole new test module seems a bit like
>> overkill just for this, but clearly we were missing test coverage here.
>> And it will come handy, if we want to invent a new better posting list
>> format in the future. Thoughts on whether to include the test module or not?
>
>
> I like the test as importantly adds missing coverage. Also, really simplifies validation effort if required to make change in this area anytime in future. So, I would +1 keeping the same.

I'd +1 too. It's valuable to test hard-to-reproduce case. I often want
to do such unit tests with more cheaper costs, though.

BTW it's not related to this patch but I got confused that where "17
bits" of the following paragraph in ginpostinglist.c comes from. If we
use only 43 bit out of 64-bit unsigned integer we have 21 bits left.

 * For encoding purposes, item pointers are represented as 64-bit unsigned
 * integers. The lowest 11 bits represent the offset number, and the next
 * lowest 32 bits are the block number. That leaves 17 bits unused, i.e.
 * only 43 low bits are used.

Regards,

--
Masahiko Sawada
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center