Horton

Re: Hash Functions

Jeff Davis <pgsql@j-davis.com>

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From: Jeff Davis <pgsql@j-davis.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Robert Haas <robertmhaas@gmail.com>, David Fetter <david@fetter.org>, Andres Freund <andres@anarazel.de>, Greg Stark <stark@mit.edu>, Amit Kapila <amit.kapila16@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Yugo Nagata <nagata@sraoss.co.jp>, amul sul <sulamul@gmail.com>
Date: 2017-05-18T06:05:15Z
Lists: pgsql-hackers 
On Wed, May 17, 2017 at 11:35 AM, Tom Lane <tgl@sss.pgh.pa.us> wrote:
> I think the question is whether we are going to make a distinction between
> logical partitions (where the data division rule makes some sense to the
> user) and physical partitions (where it needn't).  I think it might be
> perfectly reasonable for those to behave differently.

Agreed. To summarize my perspective:

* hash partitioning offers a nice way to divide the data for later
processing by parallel query
* range partitioning is good for partition elimination
(constraint_exclusion) and separating hot/cold data (e.g. partitioning
on date)
* both offer some maintenance benefits (e.g. reindex one partition at
a time), though range partitioning seems like it offers better
flexibility here in some cases

I lean toward separating the concepts, but Robert is making some
reasonable arguments and I could be convinced.

Regards,
    Jeff Davis

Commits

  1. Introduce 64-bit hash functions with a 64-bit seed.

  2. Create a "sort support" interface API for faster sorting.

  3. Add seven kanji characters defined in the Windows 950 codepage to our