Re: Incorrect comment in get_partition_dispatch_recurse

From: Amit Langote <Langote_Amit_f8(at)lab(dot)ntt(dot)co(dot)jp>
To: David Rowley <david(dot)rowley(at)2ndquadrant(dot)com>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: Robert Haas <robertmhaas(at)gmail(dot)com>, PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Incorrect comment in get_partition_dispatch_recurse
Date: 2018-05-18 01:22:25
Message-ID: 6d73cbf0-f10e-6769-7e02-b4f7a406102f@lab.ntt.co.jp
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On 2018/05/18 6:14, David Rowley wrote:
> On 18 May 2018 at 02:13, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
>> Maybe what you need is a redesign. This convention seems impossibly
>> confusing and hence error-prone. What about using a separate bool to
>> indicate which list the index refers to?
>
> While I agree that the coding is a bit unusual, I think it's also good
> that we can get away without allocating yet another array nparts in
> size. ExecSetupPartitionTupleRouting is already a huge bottleneck with
> single-row INSERT into a partitioned table with a large number of
> partitions. Allocating yet another array nparts in size will just slow
> it down further.

I recall having considered the idea of adding an array of bools, but went
with the negative-indexes-for-partitioned-tables idea anyway, which I
remember was suggested by Robert back then [1]. I admit it's a bit
confusing, but it's nice not have one more array allocation in that path
as you say.

> I have patches locally that I'll be submitting during the v12 cycle to
> improve on this. Among other things, the patches go to lengths to not
> allocate these arrays when we don't have to.

That would be nice.

Thanks,
Amit

[1]
https://www.postgresql.org/message-id/CA%2BTgmobF2r%3Df-crrE-k7WM8iFpBKLz3dtBtEc%3DKmkudYViYcyQ%40mail.gmail.com

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