hallo,
from the document, I think the determinant of each row in the partition is the residual value (partition key divided by the specified modulus)
So I think the value that will come out is not what I have listed.
The value that should come out like below ( as in the mods column )
SELECT *,(id % 3)as mods FROM myschema.customers;
id status arr mods
2 "RECURRING" 20 2
4 "REACTIVATED" 144 1
3 "EXPIRED" 38 0
1 "ACTIVE" 100 1
table cust0
id = 3
table cust1
id = 4,1
table cust2
id = 2
best regards
Yudianto
On Wed, Sep 15, 2021 at 7:08 PM Yudianto Prasetyo <mr.yudianto@gmail.com> wrote:
>
> sorry I miss the query
>
> select * from myschema.cust0;
>
> On Wed, Sep 15, 2021 at 1:28 PM Yudianto Prasetyo <mr.yudianto@gmail.com> wrote:
>>
>> Hello,
>>
>> can you explain if this is a bug or my fault ?
>>
>> I'm making a simple example of hash partition
>>
>> CREATE TABLE myschema.customers(
>> id int,
>> status text,
>> arr numeric
>> ) PARTITION BY HASH(id);
>>
>> CREATE TABLE myschema.cust0 PARTITION OF myschema.customers
>> FOR VALUES WITH (modulus 3, remainder 0);
>>
>> CREATE TABLE myschema.cust1 PARTITION OF myschema.customers
>> FOR VALUES WITH (modulus 3, remainder 1);
>>
>> CREATE TABLE myschema.cust2 PARTITION OF myschema.customers
>> FOR VALUES WITH (modulus 3, remainder 2);
>>
>> INSERT INTO myschema.customers VALUES (1,'ACTIVE',100), (2,'RECURRING',20), (3,'EXPIRED',38), (4,'REACTIVATED',144);
>>
>> when I run the query, the result is:
>>
>> 2 "RECURRING" 20
>> 4 "REACTIVATED" 144
>>
>> shouldn't be
>>
>> 3 "EXPIRED" 38
>>
>> i run this in version
>>
>> PostgreSQL 13.4, compiled by Visual C++ build 1914, 64-bit
>>
>> Please help me
I could be wrong but IIRC I have been tripped up by this before. The
docs [1] says "Each partition will hold the rows for which the hash
value of the partition key divided by the specified modulus will
produce the specified remainder.". Perhaps you were expecting it to do
the do modulus on the key, but not on the hash value of the key?
------
[1] https://www.postgresql.org/docs/13/ddl-partitioning.html
Kind Regards,
Peter Smith.
Fujitsu Australia.
