Re: [POC] hash partitioning

On Mon, Oct 9, 2017 at 5:51 PM, Ashutosh Bapat
<ashutosh.bapat@enterprisedb.com> wrote:
> On Mon, Oct 9, 2017 at 4:44 PM, amul sul <sulamul@gmail.com> wrote:
>

Thanks Ashutosh for your review, please find my comment inline.

>
>> 0002 few changes in partition-wise join code to support
>> hash-partitioned table as well & regression tests.
>
> +    switch (key->strategy)
> +    {
> +        case PARTITION_STRATEGY_HASH:
> +            /*
> +             * Indexes array is same as the greatest modulus.
> +             * See partition_bounds_equal() for more explanation.
> +             */
> +            num_indexes = DatumGetInt32(src->datums[ndatums - 1][0]);
> +            break;
> This logic is duplicated at multiple places.  I think it's time we consolidate
> these changes in a function/macro and call it from the places where we have to
> calculate number of indexes based on the information in partition descriptor.
> Refactoring existing code might be a separate patch and then add hash
> partitioning case in hash partitioning patch.
>

Make sense, added get_partition_bound_num_indexes() to get number of index
elements in 0001 & get_greatest_modulus() as name suggested to get the greatest
modulus of the hash partition bound in 0002.

> +        int        dim = hash_part? 2 : partnatts;
> Call the variable as natts_per_datum or just natts?
>

natts represents the number of attributes, but for the hash partition bound we
are not dealing with the attribute so that I have used short-form of dimension,
thoughts?

> +                                    hash_part? true : key->parttypbyval[j],
> +                                    key->parttyplen[j]);
> parttyplen is the length of partition key attribute, whereas what you want here
> is the length of type of modulus and remainder. Is that correct? Probably we
> need some special handling wherever parttyplen and parttypbyval is used e.g. in
> call to partition_bounds_equal() from build_joinrel_partition_info().
>

Unless I am missing something, I don't think we should worry about parttyplen
because in the datumCopy() when the datatype is pass-by-value then typelen
is ignored.

Regards,
Amul