Re: Removing width from EXPLAIN

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I remember there was some talk about removing the width=xxx part from the
EXPLAIN plans. Any movement towards this? I myself would like to see this
happen as it does not provide useful information and makes the already busy
explain plan that much busier. Anyone have a good argument to keep this
around? Can we at least make it display/not display with a parameter?

- --
Greg Sabino Mullane greg(at)turnstep(dot)com
PGP Key: 0x14964AC8 200305190919
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"Greg Sabino Mullane" <greg(at)turnstep(dot)com> writes:
> I remember there was some talk about removing the width=xxx part from the
> EXPLAIN plans. Any movement towards this?

You didn't hear that from me.

> I myself would like to see this
> happen as it does not provide useful information

Yes it does: the width * number of rows is a critical element in cost
estimation for sorts and hashes.

regards, tom lane

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I guess I was thinking about this:

http://groups.google.com/groups?selm=10897.953919427%40sss.pgh.pa.us

"Average width is pretty bogus because the thing really doesn't have
any idea of the average length of variable-length columns. I'm thinking
about improving that in the future, but it may not be worth the trouble,
because the width isn't used for very much."

I also think that it is used that much: if you look at all the EXPLAINS
that have come across the various lists over the years, very few (if any)
utilize the "width" in any important way. It's important for computing
the cost, but I would like to suggest that the extra "noise" should be
off by default as most people never make use of it, and an EXPLAIN ANALYZE
is already quite verbose.

- --
Greg Sabino Mullane greg(at)turnstep(dot)com
PGP Key: 0x14964AC8 200305201143

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greg(at)turnstep(dot)com writes:
> I guess I was thinking about this:
> http://groups.google.com/groups?selm=10897.953919427%40sss.pgh.pa.us
> "Average width is pretty bogus because the thing really doesn't have
> any idea of the average length of variable-length columns. I'm thinking
> about improving that in the future, but it may not be worth the trouble,
> because the width isn't used for very much."

That comment predated 7.0, which is a long time ago. We now have
statistics about actual average widths of columns, so the estimates are
not nearly as bogus as they used to be. And with the expanded scope for
hash-based query plans in 7.4, I think the estimated size of hash tables
will become an even more interesting tidbit than it is now.

> I also think that it is used that much: if you look at all the EXPLAINS
> that have come across the various lists over the years, very few (if any)
> utilize the "width" in any important way. It's important for computing
> the cost, but I would like to suggest that the extra "noise" should be
> off by default as most people never make use of it, and an EXPLAIN ANALYZE
> is already quite verbose.

But EXPLAIN has always included a lot of info that the man in the street
wouldn't know how to interpret. I don't think making it less complete
is going to help anyone.

regards, tom lane

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> That comment predated 7.0, which is a long time ago.

Yep, that's old all right. Don't know how such an old thread stuck in my
head for so long. :)

> ...
> But EXPLAIN has always included a lot of info that the man in the street
> wouldn't know how to interpret. I don't think making it less complete
> is going to help anyone.

Fair enough, I'm happy with the way it is then. FWIW, I tried to look up
the history of plan_width in the src/backend tree, but anoncvs is still down. :(

- --
Greg Sabino Mullane greg(at)turnstep(dot)com
PGP Key: 0x14964AC8 200305201517
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On Tue, May 20, 2003 at 08:14:12PM -0000, greg(at)turnstep(dot)com wrote:

> > But EXPLAIN has always included a lot of info that the man in the street
> > wouldn't know how to interpret. I don't think making it less complete
> > is going to help anyone.
>
> Fair enough, I'm happy with the way it is then. FWIW, I tried to look up
> the history of plan_width in the src/backend tree, but anoncvs is still down. :(

FWIW, if you want to try such things, I strongly recommend using CVSup.
It's not exactly easy to setup, but it's really nice to have the
complete repository.

Joe Conway has some RPMs that can be of use in www.joeconway.com, if you
are in a Redhat-ish system. Make sure you install ezm3 first...

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
Jajaja! Solo hablaba en serio!

> FWIW, if you want to try such things, I strongly recommend using CVSup.
> It's not exactly easy to setup, but it's really nice to have the
> complete repository.

How did you manage to get the earthdistance and libpqxx items?
Makefiles are broken as they don't exist in the pgsql module.

Followed:
http://developer.postgresql.org/docs/postgres/cvsup.html
--
Rod Taylor <rbt(at)rbt(dot)ca>

PGP Key: http://www.rbt.ca/rbtpub.asc

On Wed, May 21, 2003 at 02:40:17PM -0400, Rod Taylor wrote:
> > FWIW, if you want to try such things, I strongly recommend using CVSup.
> > It's not exactly easy to setup, but it's really nice to have the
> > complete repository.
>
> How did you manage to get the earthdistance and libpqxx items?
> Makefiles are broken as they don't exist in the pgsql module.

Oh, I didn't. In fact, I took them out of contrib/Makefile.

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
"El conflicto es el camino real hacia la union"

I ended up doing that too..

But of course the diffs now include those make file changes (DOH!).

On Wed, 2003-05-21 at 14:53, Alvaro Herrera wrote:
> On Wed, May 21, 2003 at 02:40:17PM -0400, Rod Taylor wrote:
> > > FWIW, if you want to try such things, I strongly recommend using CVSup.
> > > It's not exactly easy to setup, but it's really nice to have the
> > > complete repository.
> >
> > How did you manage to get the earthdistance and libpqxx items?
> > Makefiles are broken as they don't exist in the pgsql module.
>
> Oh, I didn't. In fact, I took them out of contrib/Makefile.
--
Rod Taylor <rbt(at)rbt(dot)ca>

PGP Key: http://www.rbt.ca/rbtpub.asc

Rod Taylor wrote:
> How did you manage to get the earthdistance and libpqxx items?
> Makefiles are broken as they don't exist in the pgsql module.
>
> Followed:
> http://developer.postgresql.org/docs/postgres/cvsup.html

That needs to be updated. When Marc moved those out of the main
repository, he posted a correction --

-# complete distribution, including all below
-pgsql
+# complete distribution, including all below
+repository

-- should take care of the missing folders.

Joe

On Wed, May 21, 2003 at 08:39:03PM -0700, Joe Conway wrote:
> Rod Taylor wrote:

> >Followed:
> >http://developer.postgresql.org/docs/postgres/cvsup.html
>
> That needs to be updated. When Marc moved those out of the main
> repository, he posted a correction --
>
> -# complete distribution, including all below
> -pgsql
> +# complete distribution, including all below
> +repository

I see. I now get earthdistance and libpqxx in the cvsup repository, but
to get them into the CVS copy checked out from there, I have to manually
check them out:

cd src/interfaces
cvs -d /home/alvherre/cvsup checkout interfaces/libpqxx

But it works! Thank again, Joe.

--
Alvaro Herrera (<alvherre[a]dcc.uchile.cl>)
Major Fambrough: You wish to see the frontier?
John Dunbar: Yes sir, before it's gone.

Alvaro Herrera wrote:
> I see. I now get earthdistance and libpqxx in the cvsup repository, but
> to get them into the CVS copy checked out from there, I have to manually
> check them out:
>
> cd src/interfaces
> cvs -d /home/alvherre/cvsup checkout interfaces/libpqxx
>

Actually, I just do `cvs co pgsql` and I get everything in one shot.

Joe