Re: User Interface for WAL usage data

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(dot)ntt(at)gmail(dot)com> wrote:
> >
> > At Thu, 2 Apr 2020 00:41:20 -0500, Justin Pryzby <pryzby(at)telsasoft(dot)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