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From: Sergei Kornilov <sk@zsrv.org>
To: Yudianto Prasetyo <mr.yudianto@gmail.com>
Cc: Peter Smith <smithpb2250@gmail.com>,
	PostgreSQL mailing lists <pgsql-bugs@lists.postgresql.org>
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Subject: Re: bugs or my fault
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Precedence: bulk

We don't do just id % 3, we calculate some hash value from partition key (id) and route the tuple according this hash value. Such condition for your example:

select *, satisfies_hash_partition('myschema.customers'::regclass, 3, 0, id) as modulus3_remainder0_target_partition from myschema.cust0;

Can't illustrate more at the SQL level due to the lack of a uint64 calculations. At C level we are here: https://github.com/postgres/postgres/blob/REL_13_STABLE/src/backend/partitioning/partbounds.c#L4595

regards, Sergei