Re: Add pgstathashindex() to get hash index table statistics.

On Thu, Mar 23, 2017 at 11:24 PM, Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
> Hi,
>
> On Tue, Feb 7, 2017 at 9:23 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>> On Mon, Feb 6, 2017 at 10:40 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>>>> Maybe we should call them "unused pages".
>>>
>>> +1. If we consider some more names for that column then probably one
>>> alternative could be "empty pages".
>>
>> Yeah, but I think "unused" might be better. Because a page could be
>> in use (as an overflow page or primary bucket page) and still be
>> empty.
>>
>
> Based on the earlier discussions, I have prepared a patch that would
> allow pgstathashindex() to show the number of unused pages in hash
> index. Please find the attached patch for the same. Thanks.
>

else if (opaque->hasho_flag & LH_BITMAP_PAGE)
stats.bitmap_pages++;
+ else if (PageIsEmpty(page))
+ stats.unused_pages++;

I think having this check after PageIsNew() makes more sense then
having at the place where you currently have, other than that
code-wise your patch looks okay, although I haven't tested it.

I think this should also be tracked under PostgreSQL 10 open items,
but as this is not directly a bug, so not sure, what do others think?

--
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com