Re: [POC] hash partitioning

On Fri, May 19, 2017 at 10:35 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> + * For range and list partitioned tables, datums is an array of datum-tuples
> + * with key->partnatts datums each.
> + * For hash partitioned tables, it is an array of datum-tuples with 2 datums,
> + * modulus and remainder, corresponding to a given partition.
>
> Second line is very short; reflow as one paragraph.
>
> * In case of range partitioning, it stores one entry per distinct range
> * datum, which is the index of the partition for which a given datum
> * is an upper bound.
> + * In the case of hash partitioning, the number of the entries in the indexes
> + * array is same as the greatest modulus amongst all partitions. For a given
> + * partition key datum-tuple, the index of the partition which would
> accept that
> + * datum-tuple would be given by the entry pointed by remainder produced when
> + * hash value of the datum-tuple is divided by the greatest modulus.
>
> Insert line break before the new text as a paragraph break.

The prologue is arranged as one paragraph (with a new line) per
member. Within each paragraph explanation for each partitioning
strategy starts on its own line. One paragraph per member is more
readable than separate paragraphs for each member and strategy.

>
> I don't really see why hash partitioning needs to touch
> partition_bounds_equal() at all. Why can't the existing logic work
> for hash partitioning without change?

Right now, it compares partnatts datums values for list and range. For
hash it requires to compare 2 datums remainder and modulus. So, the
difference?
Further, I suggested that we use the fact that equality of indexes
array implies equality of bounds for hash partitioning.

--
Best Wishes,
Ashutosh Bapat
EnterpriseDB Corporation
The Postgres Database Company