On 07/21/2015 04:14 PM, Alexander Korotkov wrote:
> On Tue, Jul 21, 2015 at 3:52 PM, Heikki Linnakangas <hlinnaka@iki.fi> wrote:
>
>> On 07/21/2015 02:56 PM, Alexander Korotkov wrote:
>>
>>> Probably, but currently we are in quite unlogical situation. We have
>>> default fillfactor = 90 for GiST where it has no use cases at all and
>>> effectively is just a waste of space.
>>>
>>
>> Why is it useless for GiST?
>
>
> It's because all of GiST pages are produced by page splits. So, just after
> CREATE INDEX GiST pages aren't tightly packed in average. Actually, they
> could be tightly packed by incredible coincidence, but for large indexes
> it's quite safe assumption that they are not. With GiST we don't have storm
> of page splits after index creation with fillfactor = 100. So, why should
> we reserve additional space with fillfactor = 90?
Aha, I see. Yeah, that's pretty useless. Ideally, we would make the GiST
build algorithm smarter so that it would pack the pages more tightly. I
have no idea how to do that, however.
Anyway, the fact that fillfactor is useless for GiST is more of an
argument for removing it from GiST, than for adding it to GIN.
- Heikki