Re: Partition-wise join for join between (declaratively) partitioned tables

From: Rafia Sabih <rafia(dot)sabih(at)enterprisedb(dot)com>
To: Robert Haas <robertmhaas(at)gmail(dot)com>
Cc: Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Partition-wise join for join between (declaratively) partitioned tables
Date: 2017-03-19 04:15:33
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On Sat, Mar 18, 2017 at 5:40 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> On Fri, Mar 17, 2017 at 9:15 AM, Ashutosh Bapat
> <ashutosh(dot)bapat(at)enterprisedb(dot)com> wrote:
>> This set of patches fixes both of those things.
> 0001 changes the purpose of a function and then 0007 renames it. It
> would be better to include the renaming in 0001 so that you're not
> taking multiple whacks at the same function in the same patch series.
> I believe it would also be best to include 0011's changes to
> adjust_appendrel_attrs_multilevel in 0001.
> 0002 should either add find_param_path_info() to the relevant header
> file as extern from the beginning, or it should declare and define it
> as static and then 0007 can remove those markings. It makes no sense
> to declare it as extern but put the prototype in the .c file.
> 0004 still needs to be pared down. If you want to get something
> committed this release cycle, you have to get these details taken care
> of, uh, more or less immediately. Actually, preferably, several weeks
> ago. You're welcome to maintain your own test suite locally but what
> you submit should be what you are proposing for commit -- or if not,
> then you should separate the part proposed for commit and the part
> included for dev testing into two different patches.
> In 0005's README, the part about planning partition-wise joins in two
> phases needs to be removed. This patch also contains a small change
> to partition_join.sql that belongs in 0004.
> 0008 removes direct tests against RELOPT_JOINREL almost everywhere,
> but it overlooks the new ones added to postgres_fdw.c by
> b30fb56b07a885f3476fe05920249f4832ca8da5. It should be updated to
> cover those as well, I suspect. The commit message claims that it
> will "Similarly replace RELOPT_OTHER_MEMBER_REL test with
> IS_OTHER_REL() where we want to test for child relations of all kinds,
> but in fact it makes exactly zero such substitutions.
> While I was studying what you did with reparameterize_path_by_child(),
> I started to wonder whether reparameterize_path() doesn't need to
> start handling join paths. I think it only handles scan paths right
> now because that's the only thing that can appear under an appendrel
> created by inheritance expansion, but you're changing that. Maybe
> it's not critical -- I think the worst consequences of missing some
> handling there is that we won't consider a parameterized path in some
> case where it would be advantageous to do so. Still, you might want
> to investigate a bit.
I was trying to play around with this patch and came across following
case when without the patch query completes in 9 secs and with it in
15 secs. Theoretically, I tried to capture the case when each
partition is having good amount of rows in output and each has to
build their own hash, in that case the cost of building so many hashes
comes to be more costly than having an append and then join. Thought
it might be helpful to consider this case in better designing of the
algorithm. Please feel free to point out if I missed something.

Test details:
commit: b4ff8609dbad541d287b332846442b076a25a6df
Please find the attached .sql file for the complete schema and data
and .out file for the result of explain analyse with and without

Rafia Sabih

Attachment Content-Type Size
pwj_regress_test.out application/octet-stream 25.7 KB
test_case_pwj.sql application/octet-stream 17.6 KB

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