Re: Improve new hash partition bound check error messages

On 02/02/2021 12:35, Peter Eisentraut wrote:
> I had a bit of trouble parsing the error message "every hash partition
> modulus must be a factor of the next larger modulus", so I went into the
> code, added some comments and added errdetail messages for each case.  I
> think it's a bit clearer now.

Yeah, that error message is hard to understand. This is an improvement, 
but it still took me a while to understand it.

Let's look at the example in the regression test:

-- check partition bound syntax for the hash partition
CREATE TABLE hash_parted (
     a int
) PARTITION BY HASH (a);
CREATE TABLE hpart_1 PARTITION OF hash_parted FOR VALUES WITH (MODULUS 
10, REMAINDER 0);
CREATE TABLE hpart_2 PARTITION OF hash_parted FOR VALUES WITH (MODULUS 
50, REMAINDER 1);
CREATE TABLE hpart_3 PARTITION OF hash_parted FOR VALUES WITH (MODULUS 
200, REMAINDER 2);

With this patch, you get this:

CREATE TABLE fail_part PARTITION OF hash_parted FOR VALUES WITH (MODULUS 
25, REMAINDER 3);
ERROR:  every hash partition modulus must be a factor of the next larger 
modulus
DETAIL:  The existing modulus 10 is not a factor of the new modulus 25.

CREATE TABLE fail_part PARTITION OF hash_parted FOR VALUES WITH (MODULUS 
150, REMAINDER 3);
ERROR:  every hash partition modulus must be a factor of the next larger 
modulus
DETAIL:  The new modulus 150 is not factor of the existing modulus 200.


How about this?

CREATE TABLE fail_part PARTITION OF hash_parted FOR VALUES WITH (MODULUS 
25, REMAINDER 3);
ERROR:  every hash partition modulus must be a factor of the next larger 
modulus
DETAIL:  25 is not divisible by 10, the modulus of existing partition 
"hpart_1"

CREATE TABLE fail_part PARTITION OF hash_parted FOR VALUES WITH (MODULUS 
150, REMAINDER 3);
ERROR:  every hash partition modulus must be a factor of the next larger 
modulus
DETAIL:  150 is not a factor of 200, the modulus of existing partition 
"hpart_3"

Calling the existing partition by name seems good. And this phrasing 
puts the focus on the new modulus in both variants; presumably the 
existing partition is OK and the problem is in the new definition.

- Heikki