| From: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com> |
|---|---|
| To: | Harry B <harrysungod(at)gmail(dot)com> |
| Cc: | "pgsql-generallists(dot)postgresql(dot)org" <pgsql-general(at)lists(dot)postgresql(dot)org> |
| Subject: | Re: Postgres 11, partitioning with a custom hash function |
| Date: | 2018-10-04 03:42:52 |
| Message-ID: | CAKJS1f-oj3_3HCs8KuyGL6kpm0GHLWjekT0Mzv_zWLipnsAKCg@mail.gmail.com |
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| Lists: | pgsql-general |
On 4 October 2018 at 16:22, Harry B <harrysungod(at)gmail(dot)com> wrote:
> I am still having trouble reconciling what happens under the HASH
> partitioning!. If I have text column forming the basis of PARTITIONED BY
> HASH, the HASH value used in the partitioning setup does not seem to match
> to `hashtext()` of that value
It won't match. The hash partition hash is seeded with a special const
(HASH_PARTITION_SEED) see [1].
You could likely roll your own hash ops. See [2] for an example. This
can then be used to create a hash partitioned table like [3].
[1] https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/backend/partitioning/partbounds.c#l2056
[2] https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/test/regress/sql/insert.sql#l241
[3] https://git.postgresql.org/gitweb/?p=postgresql.git;a=blob;f=src/test/regress/sql/hash_part.sql#l10
--
David Rowley http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
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