Re: [HACKERS] advanced partition matching algorithm for partition-wise join

On Thu, Feb 6, 2020 at 3:55 AM Mark Dilger <mark.dilger@enterprisedb.com> wrote:
> The patches apply and pass all tests.  A review of the patch vs. master looks reasonable.

Thanks for the review!

> The partition_join.sql test has multiple levels of partitioning, but when your patch extends that test with “advanced partition-wise join”, none of the tables for the new section have multiple levels.  I spent a little while reviewing the code and inventing multiple level partitioning tests for advanced partition-wise join and did not encounter any problems.  I don’t care whether you use this particular example, but do you want to have multiple level partitioning in the new test section?

Yes, I do.

> CREATE TABLE alpha (a double precision, b double precision) PARTITION BY RANGE (a);
> CREATE TABLE alpha_neg PARTITION OF alpha FOR VALUES FROM ('-Infinity') TO (0) PARTITION BY RANGE (b);
> CREATE TABLE alpha_pos PARTITION OF alpha FOR VALUES FROM (0) TO ('Infinity') PARTITION BY RANGE (b);
> CREATE TABLE alpha_nan PARTITION OF alpha FOR VALUES FROM ('Infinity') TO ('NaN');
> CREATE TABLE alpha_neg_neg PARTITION OF alpha_neg FOR VALUES FROM ('-Infinity') TO (0);
> CREATE TABLE alpha_neg_pos PARTITION OF alpha_neg FOR VALUES FROM (0) TO ('Infinity');
> CREATE TABLE alpha_neg_nan PARTITION OF alpha_neg FOR VALUES FROM ('Infinity') TO ('NaN');
> CREATE TABLE alpha_pos_neg PARTITION OF alpha_pos FOR VALUES FROM ('-Infinity') TO (0);
> CREATE TABLE alpha_pos_pos PARTITION OF alpha_pos FOR VALUES FROM (0) TO ('Infinity');
> CREATE TABLE alpha_pos_nan PARTITION OF alpha_pos FOR VALUES FROM ('Infinity') TO ('NaN');
> INSERT INTO alpha (a, b)
>     (SELECT * FROM
>         (VALUES (-1.0::float8), (0.0::float8), (1.0::float8), ('Infinity'::float8)) a,
>         (VALUES (-1.0::float8), (0.0::float8), (1.0::float8), ('Infinity'::float8)) b
>     );
> ANALYZE alpha;
> ANALYZE alpha_neg;
> ANALYZE alpha_pos;
> ANALYZE alpha_nan;
> ANALYZE alpha_neg_neg;
> ANALYZE alpha_neg_pos;
> ANALYZE alpha_neg_nan;
> ANALYZE alpha_pos_neg;
> ANALYZE alpha_pos_pos;
> ANALYZE alpha_pos_nan;
> CREATE TABLE beta (a double precision, b double precision) PARTITION BY RANGE (a, b);
> CREATE TABLE beta_lo PARTITION OF beta FOR VALUES FROM (-5, -5) TO (0, 0);
> CREATE TABLE beta_me PARTITION OF beta FOR VALUES FROM (0, 0) TO (0, 5);
> CREATE TABLE beta_hi PARTITION OF beta FOR VALUES FROM (0, 5) TO (5, 5);
> INSERT INTO beta (a, b)
>     (SELECT * FROM
>         (VALUES (-1.0::float8), (0.0::float8), (1.0::float8)) a,
>         (VALUES (-1.0::float8), (0.0::float8), (1.0::float8)) b
>     );
> ANALYZE beta;
> ANALYZE beta_lo;
> ANALYZE beta_me;
> ANALYZE beta_hi;
> EXPLAIN SELECT * FROM alpha INNER JOIN beta ON (alpha.a = beta.a AND alpha.b = beta.b) WHERE alpha.a = 1 AND beta.b = 1;
>                                   QUERY PLAN
> -------------------------------------------------------------------------------
>  Nested Loop  (cost=0.00..2.11 rows=1 width=32)
>    ->  Seq Scan on alpha_pos_pos alpha  (cost=0.00..1.06 rows=1 width=16)
>          Filter: ((b = '1'::double precision) AND (a = '1'::double precision))
>    ->  Seq Scan on beta_hi beta  (cost=0.00..1.04 rows=1 width=16)
>          Filter: ((b = '1'::double precision) AND (a = '1'::double precision))
> (5 rows)

Hmm, I'm not sure this is a good test case for that, because this
result would be due to partition pruning applied to each side of the
join before considering partition-wise join; you could get the same
result even with enable_partitionwise_join=off.  I think it's
important that the partition-wise join logic doesn't break this query,
though.

Best regards,
Etsuro Fujita