Date: Thu, 2 Apr 2020 01:35:40 -0500
From: Justin Pryzby <pryzby@telsasoft.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>,
	Julien Rouhaud <rjuju123@gmail.com>,
	Dilip Kumar <dilipbalaut@gmail.com>,
	Kirill Bychik <kirill.bychik@gmail.com>,
	Fujii Masao <masao.fujii@oss.nttdata.com>
Subject: Re: User Interface for WAL usage data
Message-ID: <20200402063540.GE14618@telsasoft.com>
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On Thu, Apr 02, 2020 at 11:32:16AM +0530, Amit Kapila wrote:
> On Thu, Apr 2, 2020 at 11:28 AM Kyotaro Horiguchi <horikyota.ntt@gmail.com> wrote:
> >
> > At Thu, 2 Apr 2020 00:41:20 -0500, Justin Pryzby <pryzby@telsasoft.com> wrote in
> > > Regarding v10-0004-Add-option-to-report-WAL-usage-in-EXPLAIN-and-au.patch:
> > > I think there should be additional spaces before "full" and before "bytes":
> > >
> > > >    WAL: records=2359 full page records=42 bytes=447788
> > >
> > > Compare with these:
> > >
> > >        "Sort Method: %s  %s: %ldkB\n",
> > >        "Buckets: %d (originally %d)  Batches: %d (originally %d)  Memory Usage: %ldkB\n",
> > >        "Buckets: %d  Batches: %d  Memory Usage: %ldkB\n",
> > >
> > > Otherwise "records=2359 full page records=42" is hard to parse.
> >
> > I got the same feeling seeing the line.
> 
> But isn't this same as we have BufferUsage data?  We can probably
> display it as full_page_writes or something like that.

I guess you mean this:
         Buffers: shared hit=994 read=11426 dirtied=466

Which can show shared/local/temp.  Actually I would probably make the same
suggestion for "Buffers" (if it were a new patch).  I would find this to be
pretty unfriendly output:

         Buffers: shared hit=12345 read=12345 dirtied=12345 local hit=12345 read=12345 dirtied=12345 temp hit=12345 read=12345 dirtied=12345

Adding two extra spaces "  local" and "  temp" would have helped there, so
would commas, or parenthesis, dashes or almost anything - other than a
backslash.

So I think you're right that WAL is very similar to the Buffers case, but I
suggest that's not a good example to follow, especially since you're adding a
"field" with spaces in it.

I thought maybe the "two spaces" convention predated "Buffers".  But sort has
had two spaces since it was added 2009-08-10 (9bd27b7c9).  Buffers since it was
added 2009-12-15 (cddca5ec).  And buckets since it was added 2010-02-01
(42a8ab0a).  

-- 
Justin