Re: [POC] A better way to expand hash indexes.

On Mon, Mar 20, 2017 at 8:58 PM, Mithun Cy <mithun(dot)cy(at)enterprisedb(dot)com> wrote:
> Hi Amit, Thanks for the review,
>
> On Mon, Mar 20, 2017 at 5:17 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> idea could be to make hashm_spares a two-dimensional array
>> hashm_spares[32][4] where the first dimension will indicate the split
>> point and second will indicate the sub-split number. I am not sure
>> whether it will be simpler or complex than the method used in the
>> proposed patch, but I think we should think a bit more to see if we
>> can come up with some simple technique to solve this problem.
>
> I think making it a 2-dimensional array will not be any useful in fact
> we really treat the given array 2-dimensional elements now.
>

Sure, I was telling you based on that. If you are implicitly treating
it as 2-dimensional array, it might be easier to compute the array
offsets.

> The main concern of yours I think is the calculation steps to find the
> phase of the splitpoint group the bucket belongs to.
> + tbuckets = (1 << (splitpoint_group + 2));
> + phases_beyond_bucket =
> + (tbuckets - num_bucket) / (1 << (splitpoint_group - 1));
> + return (((splitpoint_group + 1) << 2) - phases_beyond_bucket) - 1;
>

It is not only about above calculation, but also what the patch is
doing in function _hash_get_tbuckets(). By the way function name also
seems unclear (mainly *tbuckets* in the name).

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