Re: [HACKERS] [POC] hash partitioning - Mailing list pgsql-hackers

On Wed, May 17, 2017 at 6:54 PM, Ashutosh Bapat
<ashutosh.bapat@enterprisedb.com> wrote:
[...]

>
> Comments on the tests
> +#ifdef USE_ASSERT_CHECKING
> +        {
> +            /*
> +             * Hash partition bound stores modulus and remainder at
> +             * b1->datums[i][0] and b1->datums[i][1] position respectively.
> +             */
> +            for (i = 0; i < b1->ndatums; i++)
> +                Assert((b1->datums[i][0] == b2->datums[i][0] &&
> +                        b1->datums[i][1] == b2->datums[i][1]));
> +        }
> +#endif
> Why do we need extra {} here?
>

Okay, removed in the attached version.

> Comments on testcases
> +CREATE TABLE hpart_1 PARTITION OF hash_parted FOR VALUES WITH
> (modulus 8, remainder 0);
> +CREATE TABLE fail_part (LIKE hpart_1 INCLUDING CONSTRAINTS);
> +ALTER TABLE hash_parted ATTACH PARTITION fail_part FOR VALUES WITH
> (modulus 4, remainder 0);
> Probably you should also test the other-way round case i.e. create modulus 4,
> remainder 0 partition and then try to add partitions with modulus 8, remainder
> 4 and modulus 8, remainder 0. That should fail.
>

Fixed.

> Why to create two tables hash_parted and hash_parted2, you should be able to
> test with only a single table.
>

Fixed.

> +INSERT INTO hpart_2 VALUES (3, 'a');
> +DELETE FROM hpart_2;
> +INSERT INTO hpart_5_a (a, b) VALUES (6, 'a');
> This is slightly tricky. On different platforms the row may map to different
> partitions depending upon how the values are hashed. So, this test may not be
> portable on all the platforms. Probably you should add such testcases with a
> custom hash operator class which is identity function as suggested by Robert.
> This also applies to the tests in insert.sql and update.sql for partitioned
> table without custom opclass.
>

Yes, you are correct. Fixed in the attached version.

> +-- delete the faulting row and also add a constraint to skip the scan
> +ALTER TABLE hpart_5 ADD CONSTRAINT hcheck_a CHECK (a IN (5)), ALTER a
> SET NOT NULL;
> The constraint is not same as the implicit constraint added for that partition.
> I am not sure whether it's really going to avoid the scan. Did you verify it?
> If yes, then how?
>

I haven't tested that, may be I've copied blindly, sorry about that.
I don't think this test is needed again for hash partitioning, so removed.

> +ALTER TABLE hash_parted2 ATTACH PARTITION fail_part FOR VALUES WITH
> (modulus 3, remainder 2);
> +ERROR:  every hash partition modulus must be a factor of the next
> larger modulus
> We should add this test with at least two partitions in there so that we can
> check lower and upper modulus. Also, testing with some interesting
> bounds discussed earlier
> in this mail e.g. adding modulus 15 when 5, 10, 60 exist will be better than
> testing with 3, 4 and 8.
>
Similar test do exists in create_table.sql file.

> +ERROR:  cannot use collation for hash partition key column "a"
> This seems to indicate that we can not specify collation for hash partition key
> column, which isn't true. Column a here can have its collation. What's not
> allowed is specifying collation in PARTITION BY clause.
> May be reword the error as "cannot use collation for hash partitioning". or
> plain "cannot use collation in PARTITION BY clause for hash partitioning".
>
> +ERROR:  invalid bound specification for a list partition
> +LINE 1: CREATE TABLE fail_part PARTITION OF list_parted FOR VALUES W...
> +                                                        ^
> Should the location for this error be that of WITH clause like in case of range
> and list partitioned table.
>

Fixed.

> +select tableoid::regclass as part, a from hash_parted order by part;
> May be add a % 4 to show clearly that the data really goes to the partitioning
> with that remainder.
>

Fixed.

Updated patch attached.  0001-patch rebased against latest head.
0002-patch also incorporates code comments and error message changes
as per Robert's & your suggestions. Thanks !

Regards,
Amul

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