Re: User Interface for WAL usage data - Mailing list pgsql-hackers

On Fri, Apr 3, 2020 at 11:58 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Fri, Apr 3, 2020 at 1:57 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Fri, Apr 3, 2020 at 11:29 AM Amit Kapila <amit.kapila16@gmail.com> wrote:
> > >
> > > On Fri, Apr 3, 2020 at 11:14 AM Justin Pryzby <pryzby@telsasoft.com> wrote:
> > > >
> > > > 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
> > > >
> > >
> > > I think this is more close to the case of Buffers where all fields are
> > > directly related to buffers/blocks.  Here all the fields we want to
> > > display are related to WAL, so we should try to make it display
> > > similar to Buffers.
> > >
> >
> > Dilip, Julien, others, do you have any suggestions here? I think we
> > need to decide something now.  We can change a few things like from
> > 'two spaces' to 'one space' between fields later as well.
>
> I also think it is more close to the BufferUsage so better to keep
> similar to that.

+1 too for keeping consistency with BufferUsage, and adding extra
spaces if needed.

>  If we think the parsing is the problem we can keep
> '_'  in the multi-word name as shown below.
> WAL: records=n full_page_writes=n bytes=n

I'm fine with it too.

To answer Justin too:

> 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.

This could be nice, but I think that it raises some extra concerns.
There are multiple tools that parse those outputs, and having to deal
with a new and non-fixed units may cause some issues.  And probably
the non text output would also need to be displayed differently.