Re: [HACKERS] path toward faster partition pruning

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: jesper(dot)pedersen(at)redhat(dot)com, David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Rajkumar Raghuwanshi <rajkumar(dot)raghuwanshi(at)enterprisedb(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp>, Amit Langote <amitlangote09(at)gmail(dot)com>, Dilip Kumar <dilipbalaut(at)gmail(dot)com>, Beena Emerson <memissemerson(at)gmail(dot)com>, "pgsql-hackers(at)postgresql(dot)org" <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: [HACKERS] path toward faster partition pruning
Date: 2018-04-05 08:28:56
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On 2018/04/05 0:45, Jesper Pedersen wrote:
> Hi,
> On 04/04/2018 09:29 AM, David Rowley wrote:
>> Thanks for updating. I've made a pass over v49 and I didn't find very
>> much wrong with it.
>> The only real bug I found was a missing IsA(rinfo->clause, Const) in
>> the pseudoconstant check inside
>> generate_partition_pruning_steps_internal.


>> Most of the changes are comment fixes with a few stylistic changes
>> thrown which are pretty much all there just to try to shrink the code
>> a line or two or reduce indentation.
>> I feel pretty familiar with this code now and assuming the attached is
>> included I'm happy for someone else, hopefully, a committer to take a
>> look at it.

Thank you, your changes look good to me.

>> I'll leave the following notes:
>> 1. Still not sure about RelOptInfo->has_default_part. This flag is
>> only looked at in generate_partition_pruning_steps. The RelOptInfo and
>> the boundinfo is available to look at, it's just that the
>> partition_bound_has_default macro is defined in partition.c rather
>> than partition.h.

Hmm, it might not be such a bad idea to bring out the
PartitionBoundInfoData into partition.h. If we do that, we won't need the
has_default_part that the patch adds to RelOptInfo.

In the Attached v50 set, 0002 does that.

>> 2. Don't really like the new isopne variable name. It's not very
>> simple to decode, perhaps something like is_not_eq is better?

isopne does sound a bit unintelligible. I propose op_is_ne so that it
sounds consistent with the preceding member of the struct that's called
opno. I want to keep "ne" and not start calling it not_eq, as a few other
places use the string "ne" to refer to a similar thing, like:

/* inequality */


Since the field is local to partprune.c, I guess that it's fine as the
comment where it's defined tells what it is.

>> 3. The part of the code I'm least familiar with is
>> get_steps_using_prefix_recurse(). I admit to not having had time to
>> fully understand that and consider ways to break it.

The purpose of that code is to generate *all* needed steps to be combined
using COMBINE_INTERSECT such that the pruning will occur using the most
restrictive set of clauses in cases where the same key is referenced in
multiple restriction clauses containing non-equality operators. So, for a
range partitioned table on (a, b):

For a query like

explain select * from foo a <= 1 and a <= 3 and b < 5 and b <= 10

Pruning steps generated to be combined with an enclosing INTERSECT step
will be as follows:

<= (1, 10)
< (1, 5)
<= (3, 10)
< (3, 5)

>> Marking as ready for committer.

Thank you!

> Passes check-world, and CommitFest app has been updated to reflect the
> current patch set. Trivial changes attached.

Merged these changes. Thanks again Jesper.

Attached v50.


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