Re: Next Steps with Hash Indexes

On Wed, Oct 27, 2021 at 2:32 AM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Tue, Oct 5, 2021 at 6:50 AM Simon Riggs <simon(dot)riggs(at)enterprisedb(dot)com> wrote:
> > With unique data, starting at 1 and monotonically ascending, hash
> > indexes will grow very nicely from 0 to 10E7 rows without causing >1
> > overflow block to be allocated for any bucket. This keeps the search
> > time for such data to just 2 blocks (bucket plus, if present, 1
> > overflow block). The small number of overflow blocks is because of the
> > regular and smooth way that splits occur, which works very nicely
> > without significant extra latency.
>
> It is my impression that with non-unique data things degrade rather
> badly.
>

But we will hold the bucket lock only for unique-index in which case
there shouldn't be non-unique data in the index. The non-unique case
should work as it works today. I guess this is the reason Simon took
an example of unique data.

--
With Regards,
Amit Kapila.