Date: Fri, 3 Apr 2020 00:44:51 -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: <20200403054451.GN14618@telsasoft.com>
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On Fri, Apr 03, 2020 at 10:52:02AM +0530, Amit Kapila wrote:
> On Fri, Apr 3, 2020 at 10:41 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
> >
> > > > > > > >    WAL: records=2359 full page records=42 bytes=447788
> >
> > 1) records; 2) pages ("full page images"); 3) bytes
> >
> > That is exactly like sort (method/type/size) and hash (buckets/batches/size),
> > and *not* like buffers, which shows various values all in units of "pages".
> >
> 
> The way you have written (2) appears to bit awkward. I would prefer
> "full page writes" or "full page images".

I didn't mean it to be the description used in the patch or anywhere else, just
the list of units.

I wonder if it should use colons instead of equals ?  As in:
|    WAL: Records: 2359  Full Page Images: 42  Size: 437kB

Note, that has: 1) two spaces; 2) capitalized "fields"; 3) size rather than
"bytes".  That's similar to Buckets:
|    Buckets: 1024  Batches: 1  Memory Usage: 44kB

I'm not sure if it should say "WAL: " or "WAL ", or perhaps "WAL:  "  If
there's no colon, then it looks like the first field is "WAL Records", but then
"size" isn't as tightly associated with WAL.  It could say:
|    WAL Records: n  Full Page Images: n  WAL Size: nkB

For comparison, buffers uses "equals" for the case showing multiple "fields",
which are all in units of pages:
|    Buffers: shared hit=15 read=2006

Also, for now, the output can be in kB, but I think in the future we should
take a recent suggestion from Andres to make an ExplainPropertyBytes() which
handles conversion to and display of a reasonable unit.  

-- 
Justin