Re: pgsql: Add EXPLAIN (MEMORY) to report planner memory consumption

Many thanks, Justin, for the post-commit review.

On 2024-Feb-06, Ashutosh Bapat wrote:

> On Tue, Feb 6, 2024 at 3:51 AM Justin Pryzby <pryzby(at)telsasoft(dot)com> wrote:
> >
> > Up to now, the explain " " (two space) format is not mixed with "=".
> >
> > And, other places which show "Memory" do not use "=". David will
> > remember prior discussions.
> > https://www.postgresql.org/message-id/20200402054120.GC14618@telsasoft.com
> > https://www.postgresql.org/message-id/20200407042521.GH2228@telsasoft.com
> >
> > "Memory: used=%lld bytes allocated=%lld bytes",
> > vs
> > "Buckets: %d (originally %d) Batches: %d (originally %d) Memory Usage: %ldkB\n",
>
> I have used = to be consistent with Buffers usage in the same Planning section.
>
> Are you suggesting that
> "Memory: used=%lld bytes allocated=%lld bytes",
> should be used instead of
> "Memory: used=%lld bytes allocated=%lld bytes",
> Please notice the single vs double space.

I think using a single space here would be confusing. It's not a
problem for show_wal_usage because that one doesn't print units.
I don't know it was you (Ashutosh) or I that put the double space, but I
considered the matter and determined that two were better.

In the new line we have two different separators (: and =) because there
are two levels of info being presented; in the show_hash_info one we
have only one type of separator.

I'm not saying this is final and definite. I'm just saying I did
consider this whole format issue and what you see is the conclusion I
reached. It may or may not be what Ashutosh submitted -- I don't
remember. As committer, I almost always tweak submitted patches, and I
won't apologize for that. Further patches to correct my mistakes and
bad decisions always welcome.

> > (Also, I first thought that "peek" should be "peak", but eventually I
> > realized that's it's as intended.)
>
> Don't understand the context. But probably it doesn't matter.

Source code always matters. Why would people spend so much time fixing
typos otherwise?

src/backend/commands/explain.c:
static bool peek_buffer_usage(ExplainState *es, const BufferUsage *usage);

We don't want to know what the "peak" buffer usage is, but we want to
"peek" whether buffer usage would print anything. I did have to spent a
minute thinking what the correct spelling was, here (but my English is
almost exclusively read/written, not spoken. Condolencies if you've had
to suffer my spoken English at some conference or whatever). I didn't
look at the dictionary back then, but now I do:
https://www.merriam-webster.com/dictionary/peek
As Justin says, it's the right word.

--
Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
"After a quick R of TFM, all I can say is HOLY CR** THAT IS COOL! PostgreSQL was
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learning new features and techniques made available by the continuing work of
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Berend Tober, http://archives.postgresql.org/pgsql-hackers/2007-08/msg01009.php