From: | Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp> |
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To: | David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
Cc: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, Amit Langote <amitlangote09(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: executor relation handling |
Date: | 2018-10-09 07:31:06 |
Message-ID: | e18887d6-b0a1-bbed-6f87-edf5faa8c317@lab.ntt.co.jp |
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Lists: | pgsql-hackers |
On 2018/10/08 9:29, David Rowley wrote:
> On 8 October 2018 at 13:13, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> The idea I had in mind was to allow hard pruning of any leaf that's
>> been excluded *at plan time* based on partition constraints seen in
>> its parent rel(s). That should be safe enough as long as we take
>> locks on all the non-leaf rels --- then we'd know about any change
>> in the constraint situation.
>>
>> Rather than coping with renumbering the RTEs, it might be easiest
>> to invent an "RTE_DUMMY" RTE type that a hard-pruned RTE could be
>> changed to.
>
> The problem with that is that, if we get [1] done in PG12, then the
> RTE_DUMMYs would not exist, as we'd only have RTEs in the range table
> for partitions that survived plan-time pruning.
...
> [1] https://commitfest.postgresql.org/20/1778/
Yeah, the patch proposed at [1] postpones creating partition RTEs (hence
locking them) to a point after pruning, which also means we create only
the necessary RTEs. In fact, it's not just the RTEs, but child
PlanRowMarks, whose creation is postponed to after pruning. So, I
admitted upthread that my proposed patch here would only add code that
will become useless if we're able to get [1] in.
Thanks,
Amit
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