Re: Problem with default partition pruning

From: Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>
To: Amit Langote <amitlangote09(at)gmail(dot)com>
Cc: yuzuko <yuzukohosoya(at)gmail(dot)com>, shawn wang <shawn(dot)wang(dot)pg(at)gmail(dot)com>, Shawn Wang <shawn(dot)wang(at)highgo(dot)ca>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Problem with default partition pruning
Date: 2019-08-04 06:29:25
Message-ID: 20190804062925.GA5861@alvherre.pgsql
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On 2019-Jul-03, Amit Langote wrote:

> Hosoya-san,
> Thanks for updating the patches.
> I have no comment in particular about
> v4_default_partition_pruning.patch,

Cool, thanks. I spent some time reviewing this patch (the first one)
and I propose the attached cosmetic changes. Mostly they consist of a
few comment rewordings.

There is one Assert() that changed in a pretty significant way ...
innocent though the change looks. The original (not Hosoya-san's
patch's fault) had an assertion which is being changed thus:

minoff = 0;
maxoff = boundinfo->ndatums;
if (partindices[minoff] < 0)
if (partindices[maxoff] < 0)

result->scan_default = partition_bound_has_default(boundinfo);
- Assert(minoff >= 0 && maxoff >= 0);
+ Assert(partindices[minoff] >= 0 &&
+ partindices[maxoff] >= 0);

Note that the original Assert() here was verifying whether minoff and
maxoff are both >= 0. But that seems pretty useless since it seems
almost impossible to have them become that given what we do to them.
What I think this code *really* wants to check is whether *the partition
indexes* that they point to are not negative: the transformation that
the two "if" lines do means to ignore bounds that correspond to value
ranges uncovered by any partition. And after the incr/decr operators,
we expect that the bounds will be those of existing partitions ... so
they shouldn't be -1.

Other changes are addition of braces to some one-line blocks that had
significant comments, and minor code rearrangements to make things look
more easily understandable.

Álvaro Herrera
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Attachment Content-Type Size
v4-delta.patch text/x-diff 6.9 KB

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