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

Thank you Fujita San for the enhancement, will have a look.

Regards,
Amul

On Wed, Aug 28, 2019 at 3:52 PM Etsuro Fujita <etsuro.fujita@gmail.com>
wrote:

> On Fri, Aug 16, 2019 at 10:25 PM Etsuro Fujita <etsuro.fujita@gmail.com>
> wrote:
> > It seems that I performed the above tests on an assertion-enabled
> > build.  :(  So I executed the tests one more time.  Here are the
> > results.
> >
> > * 2-way self-join of pt: explain analyze select * from pt t0, pt t1
> > where t0.a = t1.a;
> >  - HEAD:
> >  Planning Time: 0.969 ms
> >  Execution Time: 13.843 ms
> >  - with patch:
> >  Planning Time: 1.720 ms
> >  Execution Time: 14.393 ms
> >  - with patch plus attached:
> >  Planning Time: 1.630 ms
> >  Execution Time: 14.002 ms
> >
> > * 4-way self-join of pt: explain analyze select * from pt t0, pt t1,
> > pt t2, pt t3 where t0.a = t1.a
> >
> > and t1.a = t2.a and t2.a = t3.a;
> >  - HEAD:
> >  Planning Time: 12.203 ms
> >  Execution Time: 31.784 ms
> >  - with patch:
> >  Planning Time: 32.102 ms
> >  Execution Time: 32.504 ms
> >  - with patch plus attached:
> >  Planning Time: 19.471 ms
> >  Execution Time: 32.582 ms
> >
> > * 8-way self-join of pt: explain analyze select * from pt t0, pt t1,
> > pt t2, pt t3, pt t4, pt t5, pt t6, pt t7 where t0.a = t1.a and t1.a =
> > t2.a and t2.a = t3.a and t3.a = t4.a and t4.a = t5.a and t5.a = t6.a
> > and t6.a = t7.a;
> >  - HEAD:
> >  Planning Time: 948.131 ms
> >  Execution Time: 55.645 ms
> >  - with patch:
> >  Planning Time: 2939.813 ms
> >  Execution Time: 56.760 ms
> >  - with patch plus attached:
> >  Planning Time: 1108.076 ms
> >  Execution Time: 55.750 ms
> >
> > Note: the attached patch still uses the proposed partition matching
> > algorithm for these queries.  As I said before, these queries don't
> > need that algorithm, so we could eliminate the planning overhead
> > compared to HEAD, by planning these queries as before, perhaps, but I
> > haven't modified the patch as such yet.
>
> I modified the patch further as such.  Attached is an updated version
> of the patch created on top of the patch in [1].  I did the tests
> again using the updated version of the patch.  Here are the results:
>
> * 2-way self-join of pt:
>  Planning Time: 1.043 ms
>  Execution Time: 13.931 ms
>
> * 4-way self-join of pt:
>  Planning Time: 12.499 ms
>  Execution Time: 32.392 ms
>
> * 8-way self-join of pt:
>  Planning Time: 968.412 ms
>  Execution Time: 56.328 ms
>
> The planning time for each test case still increased slightly, but IMO
> I think that would be acceptable.  To see the efficiency of the
> attached, I did another testing with test cases that really need the
> new partition-matching algorithm:
>
> * explain analyze select * from pt6 t6, pt7 t7 where t6.a = t7.a;
>  - base patch in [1]
>  Planning Time: 1.758 ms
>  Execution Time: 13.977 ms
>  - with attached
>  Planning Time: 1.777 ms
>  Execution Time: 13.959 ms
>
> * explain analyze select * from pt4 t4, pt5 t5, pt6 t6, pt7 t7 where
> t4.a = t5.a and t5.a = t6.a and t6.a = t7.a;
>  - base patch in [1]
>  Planning Time: 33.201 ms
>  Execution Time: 32.480 ms
>  - with attached
>  Planning Time: 21.019 ms
>  Execution Time: 32.777 ms
>
> * explain analyze select * from pt0 t0, pt1 t1, pt2 t2, pt3 t3, pt4
> t4, pt5 t5, pt6 t6, pt7 t7 where t0.a = t1.a and t1.a = t2.a and t2.a
> = t3.a and t3.a = t4.a and t4.a = t5.a and t5.a = t6.a and t6.a =
> t7.a;
>  - base patch in [1]
>  Planning Time: 3060.000 ms
>  Execution Time: 55.553 ms
>  - with attached
>  Planning Time: 1144.996 ms
>  Execution Time: 56.233 ms
>
> where pt0, pt1, pt2, pt3, pt4, pt5, pt6 and pt7 are list partitioned
> tables that have slighly different list values.  (The structure and
> list values of ptN are almost the same as that of pt used above, but
> ptN's N-th partition ptNpN has an extra list value that pt's N-th
> partition ptpN doesn't have.)  If anyone is interested in this
> testing, I'll send a script file for producing these list partitioned
> tables.
>
> About the attached:
>
> * The attached patch modified try_partitionwise_join() so that we call
> partition_bounds_equal() then partition_bounds_merge() (if necessary)
> to create the partition bounds for the join rel.  We don't support for
> merging the partition bounds for the hash-partitioning case, so this
> makes code to handle the hash-partitioning case in
> partition_bounds_merge() completely unnecessary, so I removed that
> entirely.
>
> * I removed this assertion in partition_bounds_merge(), because I
> think this is covered by two assertions above this.
>
> +   Assert((*outer_parts == NIL || *inner_parts != NIL) &&
> +          (*inner_parts == NIL || *outer_parts != NIL));
>
> * (I forgot to mention this in a previous email, but) I removed this
> bit of generate_matching_part_pairs(), because we already have the
> same check in try_partitionwise_join(), so this bit would be redundant
> IIUC.
>
> +       switch (jointype)
> +       {
> +           case JOIN_INNER:
> +           case JOIN_SEMI:
> +
> +               /*
> +                * An inner or semi join can not return any row when the
> +                * matching partition on either side is missing. We should
> +                * have eliminated all such cases while merging the bounds.
> +                */
> +               Assert(part1 >= 0 && part2 >= 0);
> +               break;
> +
> +           case JOIN_LEFT:
> +           case JOIN_ANTI:
> +               Assert(part1 >= 0);
> +               if (part2 < 0)
> +                   merged = false;
> +               break;
> +
> +           case JOIN_FULL:
> +               if (part1 < 0 || part2 < 0)
> +                   merged = false;
> +               break;
> +
> +           default:
> +               elog(ERROR, "unrecognized join type: %d", (int) jointype);
> +       }
>
> * I added more comments.
>
> If there are no objections, I'll merge the attached with the base patch in
> [1].
>
> Best regards,
> Etsuro Fujita
>
> [1]
> https://www.postgresql.org/message-id/CAPmGK177W%2BjNgpM5f_m-vdDKbEBu_%3D3CyPzFjkT_1nzf1Vqn%2BA%40mail.gmail.com
>