From: Dean Rasheed <dean.a.rasheed@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Aleksander Alekseev <aleksander@timescale.com>
Cc: pgsql-hackers@lists.postgresql.org, Chantal Keller <chantal.keller@universite-paris-saclay.fr>
Subject: Re: Improving EXPLAIN's display of SubPlan nodes
Date: Mon, 18 Mar 2024 14:29:21 +0000
Message-ID: <CAEZATCULqMzbME2UEpybnBnp_U_6Yaa2Zm1BFuPFXKUq4-RXhw@mail.gmail.com> (raw)
In-Reply-To: <3399753.1710704359@sss.pgh.pa.us>
References: <2838538.1705692747@sss.pgh.pa.us>
<CAJ7c6TMApZ62NOOk73_BmKkKtdhV+i=tyvXR52DAB-YVuFANDA@mail.gmail.com>
<3791430.1705943243@sss.pgh.pa.us>
<3831858.1705959108@sss.pgh.pa.us>
<3511300.1708112330@sss.pgh.pa.us>
<CAEZATCUQB3ybgBxEHXq28ihMS3+Bq-Gy8RraJpKGmVpjES6E3A@mail.gmail.com>
<2506269.1710514705@sss.pgh.pa.us>
<2982030.1710609907@sss.pgh.pa.us>
<CAEZATCVa63moqwsi37a6LKj9mDsnbzEUw0KJYT8Qe2OZ-7V+Jg@mail.gmail.com>
<3127158.1710685722@sss.pgh.pa.us>
<3399753.1710704359@sss.pgh.pa.us>
On Sun, 17 Mar 2024 at 19:39, Tom Lane <tgl@sss.pgh.pa.us> wrote:
>
> Here's a cleaned-up version that seems to successfully resolve
> PARAM_EXEC references in all cases. I haven't changed the
> "(plan_name).colN" notation, but that's an easy fix once we have
> consensus on the spelling.
I took a more detailed look at this and the code and doc changes all
look good to me.
There's a comment at the end of find_param_generator() that should
probably say "No generator found", rather than "No referent found".
The get_rule_expr() code could perhaps be simplified a bit, getting
rid of the show_subplan_name variable and moving the recursive calls
to get_rule_expr() to after the switch statement -- if testexpr is
non-NULL, print it, else print the subplan name probably works for all
subplan types.
The "colN" notation has grown on me, especially when you look at
examples like those in partition_prune.out with a mix of Param types.
Not using "$n" for 2 different purposes is good, and I much prefer
this to the original "FROM [HASHED] SubPlan N (returns ...)" notation.
> There are two other loose ends bothering me:
>
> 1. I see that Gather nodes sometimes print things like
>
> -> Gather (actual rows=N loops=N)
> Workers Planned: 2
> Params Evaluated: $0, $1
> Workers Launched: N
>
> I propose we nuke the "Params Evaluated" output altogether.
+1
> 2. MULTIEXPR_SUBLINK subplans now result in EXPLAIN output like
>
> -> Result
> Output: (SubPlan 1).col1, (SubPlan 1).col2, (SubPlan 1), i.tableoid, i.ctid
>
> The undecorated reference to (SubPlan 1) is fairly confusing, since
> it doesn't correspond to anything that will actually get output.
> I suggest that perhaps instead this should read
>
> Output: (SubPlan 1).col1, (SubPlan 1).col2, IGNORE(SubPlan 1), i.tableoid, i.ctid
>
> or
>
> Output: (SubPlan 1).col1, (SubPlan 1).col2, RESET(SubPlan 1), i.tableoid, i.ctid
I think "RESET()" or "RESCAN()" or something like that is better than
"INGORE()", because it indicates that it is actually doing something.
I don't really have a better idea. Perhaps not all uppercase though,
since that seems to go against the rest of the EXPLAIN output.
Regards,
Dean
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: dean.a.rasheed@gmail.com, tgl@sss.pgh.pa.us, aleksander@timescale.com, chantal.keller@universite-paris-saclay.fr
Subject: Re: Improving EXPLAIN's display of SubPlan nodes
In-Reply-To: <CAEZATCULqMzbME2UEpybnBnp_U_6Yaa2Zm1BFuPFXKUq4-RXhw@mail.gmail.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox