Re: explain plans with information about (modified) gucs

From: Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com>
To: Rafia Sabih <rafia(dot)pghackers(at)gmail(dot)com>
Cc: Michael Paquier <michael(at)paquier(dot)xyz>, John Naylor <john(dot)naylor(at)2ndquadrant(dot)com>, Sergei Agalakov <sergei(dot)agalakov(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: explain plans with information about (modified) gucs
Date: 2019-03-26 20:04:53
Message-ID: 20190326200453.GA16551@development
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On Mon, Mar 18, 2019 at 11:31:48AM +0100, Rafia Sabih wrote:
>On Sun, 24 Feb 2019 at 00:06, Tomas Vondra <tomas(dot)vondra(at)2ndquadrant(dot)com> wrote:
>> Hi,
>> attached is an updated patch, fixing and slightly tweaking the docs.
>> Barring objections, I'll get this committed later next week.
>I was having a look at this patch, and this kept me wondering,
>+static void
>+ExplainShowSettings(ExplainState *es)
>Is there some reason for not providing any explanation above this
>function just like the rest of the functions in this file?
>Similarly, for
>struct config_generic **
>get_explain_guc_options(int *num)
>/* also bail out of there are no options */
>+ if (!num)
>+ return;
>I think you meant 'if' instead if 'of' here.

Thanks for the review - attached is a patch adding the missing comments,
and doing two additional minor improvements:

1) Renaming ExplainShowSettings to ExplainPrintSettings, to make it more
consistent with naming of the other functions in explain.c.

2) Actually counting GUC_EXPLAIN options, and only allocating space for
those in get_explain_guc_options, instead of using num_guc_variables. The
diffrence is quite significant (~50 vs. ~300), and considering each entry
is 8B it makes a difference because such large chunks tend to have higher
palloc overhed (due to ALLOCSET_SEPARATE_THRESHOLD).


Tomas Vondra
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Attachment Content-Type Size
explain-with-settings-20190326.patch text/plain 4.0 KB

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