controlling psql's use of the pager a bit more

On 13 November 2014 15:52, Andrew Dunstan <andrew@dunslane.net> wrote:

I often get annoyed because psql is a bit too aggressive when it decides
whether to put output through the pager, and the only way to avoid this is
to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify a
minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

+1

I've found this annoying myself.
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Andrew Dunstan <andrew@dunslane.net> writes:

I often get annoyed because psql is a bit too aggressive when it decides
whether to put output through the pager, and the only way to avoid this
is to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify
a minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the window
height? Why?

My impression is that the problem is not with the threshold as such,
it's that psql is not terribly careful about determining how many lines
it will put out (ie, the value being compared to the threshold isn't
100% reliable). If that's correct, then a hand-set threshold isn't
really going to make you happier, and what's needed is some hard work
on improving the quality of the lines-to-be-output estimates.

regards, tom lane

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On 2014-11-13 11:09:06 -0500, Tom Lane wrote:

Andrew Dunstan <andrew@dunslane.net> writes:

I often get annoyed because psql is a bit too aggressive when it decides
whether to put output through the pager, and the only way to avoid this
is to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify
a minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the window
height? Why?

Not sure what that'd be useful for.

What I've noticed more than once is that it'd be useful to force the
pager if the result is wider than the screen.

My impression is that the problem is not with the threshold as such,
it's that psql is not terribly careful about determining how many lines
it will put out (ie, the value being compared to the threshold isn't
100% reliable). If that's correct, then a hand-set threshold isn't
really going to make you happier, and what's needed is some hard work
on improving the quality of the lines-to-be-output estimates.

If it's that, I've personally solved that problem for me by adding -F
(aka --quit-if-one-screen) to $LESS.

Greetings,

Andres Freund

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On 11/13/2014 11:09 AM, Tom Lane wrote:

Andrew Dunstan <andrew@dunslane.net> writes:

I often get annoyed because psql is a bit too aggressive when it decides
whether to put output through the pager, and the only way to avoid this
is to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify
a minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the window
height? Why?

Because I might be quite happy with 100 or 200 lines I can just scroll
in my terminal's scroll buffer, but want to use the pager for more than
that. This is useful especially if I want to scroll back and see the
results from a query or two ago.

cheers

andrew

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On Thu, Nov 13, 2014 at 05:14:47PM +0100, Andres Freund wrote:

On 2014-11-13 11:09:06 -0500, Tom Lane wrote:

Andrew Dunstan <andrew@dunslane.net> writes:

I often get annoyed because psql is a bit too aggressive when it decides
whether to put output through the pager, and the only way to avoid this
is to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify
a minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the window
height? Why?

Not sure what that'd be useful for.

If the output is of the same order of magnitude as the window height, it
is still easy to compare the new output with whatever was above it by
conventional terminal scrolling (pgup, screen scrolling, whatever, if
present). If a comparison is desired in the first place, that is.

If the output goes to the pager, you're stuck with it. Unless of course
if the pager could somehow include the previous output up to some
threshold (while still being positioned at the beginning of the new
output in order to retain current behaviour), so one could scroll up in
the pager window. That would rock.

Michael

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Andrew Dunstan wrote

On 11/13/2014 11:09 AM, Tom Lane wrote:

Andrew Dunstan &lt;

andrew@

&gt; writes:

I often get annoyed because psql is a bit too aggressive when it decides
whether to put output through the pager, and the only way to avoid this
is to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify
a minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the window
height? Why?

Because I might be quite happy with 100 or 200 lines I can just scroll
in my terminal's scroll buffer, but want to use the pager for more than
that. This is useful especially if I want to scroll back and see the
results from a query or two ago.

+1

David J.

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On Thu, Nov 13, 2014 at 11:54 AM, David G Johnston
<david.g.johnston@gmail.com> wrote:

Because I might be quite happy with 100 or 200 lines I can just scroll
in my terminal's scroll buffer, but want to use the pager for more than
that. This is useful especially if I want to scroll back and see the
results from a query or two ago.

+1

+1 from me, too.

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On Thu, Nov 13, 2014 at 11:39 AM, Robert Haas <robertmhaas@gmail.com> wrote:

On Thu, Nov 13, 2014 at 11:54 AM, David G Johnston
<david.g.johnston@gmail.com> wrote:

Because I might be quite happy with 100 or 200 lines I can just scroll
in my terminal's scroll buffer, but want to use the pager for more than
that. This is useful especially if I want to scroll back and see the
results from a query or two ago.

+1

+1 from me, too.

me three (as long as the current behaviors are not messed with and the
new stuff is 'opt in' somehow -- I also use the force quit option to
less).

merlin

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On Thu, Nov 13, 2014 at 10:55 AM, Merlin Moncure <mmoncure@gmail.com> wrote:

On Thu, Nov 13, 2014 at 11:39 AM, Robert Haas <robertmhaas@gmail.com>
wrote:

On Thu, Nov 13, 2014 at 11:54 AM, David G Johnston
<david.g.johnston@gmail.com> wrote:

Because I might be quite happy with 100 or 200 lines I can just scroll
in my terminal's scroll buffer, but want to use the pager for more than
that. This is useful especially if I want to scroll back and see the
results from a query or two ago.

+1

+1 from me, too.

me three (as long as the current behaviors are not messed with and the
new stuff is 'opt in' somehow -- I also use the force quit option to
less).

​Being able to use "\pset pager"​

​to toggle the capability seems useful.

Thus I'd suggest establishing a new "pager_minlines"​ option that if unset
(default) maintains the current behavior but which can have a value (0 to
int_max) where 0 ends up basically doing the same thing as "always" mode
for "pager". Leaving the value blank will cause the option to be unset
again and revert to the current behavior.

David J.

On Thu, Nov 13, 2014 at 7:52 AM, Andrew Dunstan <andrew@dunslane.net> wrote:

I often get annoyed because psql is a bit too aggressive when it decides
whether to put output through the pager, and the only way to avoid this is
to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify a
minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

+1.

If it scrolls 2 or 3 lines off the top, I can just use the scroll-back
buffer to look at them, I don't want the pager for that situation.

But I am more interested in width, not length. I don't want it to switch
to the pager just because a couple lines would wrap, especially when
looking at EXPLAIN output. I have played with changing \pset columns, but
then other things get screwy once you set that to a non-actual value. I
don't recall of the top of my head which things those are, though.

Cheers,

Jeff

On Thu, Nov 13, 2014 at 8:14 AM, Andres Freund <andres@2ndquadrant.com>
wrote:

On 2014-11-13 11:09:06 -0500, Tom Lane wrote:

Andrew Dunstan <andrew@dunslane.net> writes:

I often get annoyed because psql is a bit too aggressive when it

decides

whether to put output through the pager, and the only way to avoid this
is to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify
a minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the window
height? Why?

Not sure what that'd be useful for.

What I've noticed more than once is that it'd be useful to force the
pager if the result is wider than the screen.

For which formats do you want that? It is already done that way under
\pset format aligned.

Cheers,

Jeff

On Thu, Nov 13, 2014 at 12:03 PM, David Johnston
<david.g.johnston@gmail.com> wrote:

On Thu, Nov 13, 2014 at 10:55 AM, Merlin Moncure <mmoncure@gmail.com> wrote:

On Thu, Nov 13, 2014 at 11:39 AM, Robert Haas <robertmhaas@gmail.com>
wrote:

On Thu, Nov 13, 2014 at 11:54 AM, David G Johnston
<david.g.johnston@gmail.com> wrote:

Because I might be quite happy with 100 or 200 lines I can just scroll
in my terminal's scroll buffer, but want to use the pager for more
than
that. This is useful especially if I want to scroll back and see the
results from a query or two ago.

+1

+1 from me, too.

me three (as long as the current behaviors are not messed with and the
new stuff is 'opt in' somehow -- I also use the force quit option to
less).

Being able to use "\pset pager"

to toggle the capability seems useful.

Thus I'd suggest establishing a new "pager_minlines" option that if unset
(default) maintains the current behavior but which can have a value (0 to
int_max) where 0 ends up basically doing the same thing as "always" mode for
"pager". Leaving the value blank will cause the option to be unset again
and revert to the current behavior.

seems pretty reasonable.

merlin

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On 11/13/2014 11:41 AM, Andrew Dunstan wrote:

On 11/13/2014 11:09 AM, Tom Lane wrote:

Andrew Dunstan <andrew@dunslane.net> writes:

I often get annoyed because psql is a bit too aggressive when it
decides
whether to put output through the pager, and the only way to avoid this
is to turn the pager off (in which case your next query might dump many
thousands of lines to the screen). I'd like a way to be able to specify
a minumum number of lines of output before psql would invoke the pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the window
height? Why?

Because I might be quite happy with 100 or 200 lines I can just scroll
in my terminal's scroll buffer, but want to use the pager for more
than that. This is useful especially if I want to scroll back and see
the results from a query or two ago.

This patch shows more or less what I had in mind.

However, there is more work to do. As Tom noted upthread, psql's
calculation of the number of lines is pretty bad. For example, if I do:

\pset pager_min_lines 100
select * from generate_series(1,50);

the pager still gets invoked, which is unfortunate to say the least.

So I'm going to take a peek at that.

cheers

andrew

Andrew Dunstan wrote:

However, there is more work to do. As Tom noted upthread, psql's calculation
of the number of lines is pretty bad. For example, if I do:

\pset pager_min_lines 100
select * from generate_series(1,50);

the pager still gets invoked, which is unfortunate to say the least.

So I'm going to take a peek at that.

Any luck there?

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On 12/04/2014 03:53 PM, Alvaro Herrera wrote:

Andrew Dunstan wrote:

However, there is more work to do. As Tom noted upthread, psql's calculation
of the number of lines is pretty bad. For example, if I do:

\pset pager_min_lines 100
select * from generate_series(1,50);

the pager still gets invoked, which is unfortunate to say the least.

So I'm going to take a peek at that.

Any luck there?

Some, yes, See
<http://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=4077fb4d1d34ad04dfb95ba676c2b43ea1f1da53&gt;

cheers

andrew

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On 11/15/2014 05:56 PM, Andrew Dunstan wrote:

On 11/13/2014 11:41 AM, Andrew Dunstan wrote:

On 11/13/2014 11:09 AM, Tom Lane wrote:

Andrew Dunstan <andrew@dunslane.net> writes:

I often get annoyed because psql is a bit too aggressive when it
decides
whether to put output through the pager, and the only way to avoid
this
is to turn the pager off (in which case your next query might dump
many
thousands of lines to the screen). I'd like a way to be able to
specify
a minumum number of lines of output before psql would invoke the
pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the
window
height? Why?

Because I might be quite happy with 100 or 200 lines I can just
scroll in my terminal's scroll buffer, but want to use the pager for
more than that. This is useful especially if I want to scroll back
and see the results from a query or two ago.

This patch shows more or less what I had in mind.

However, there is more work to do. As Tom noted upthread, psql's
calculation of the number of lines is pretty bad. For example, if I do:

\pset pager_min_lines 100
select * from generate_series(1,50);

the pager still gets invoked, which is unfortunate to say the least.

So I'm going to take a peek at that.

The over-eager invocation of the pager due to double counting of lines
got fixed recently, so here's a slightly updated patch for a
pager_min_lines setting, including docco.

cheers

andrew

On 12/21/2014 02:22 PM, Andrew Dunstan wrote:

On 11/15/2014 05:56 PM, Andrew Dunstan wrote:

On 11/13/2014 11:41 AM, Andrew Dunstan wrote:

On 11/13/2014 11:09 AM, Tom Lane wrote:

Andrew Dunstan <andrew@dunslane.net> writes:

I often get annoyed because psql is a bit too aggressive when it
decides
whether to put output through the pager, and the only way to avoid
this
is to turn the pager off (in which case your next query might dump
many
thousands of lines to the screen). I'd like a way to be able to
specify
a minumum number of lines of output before psql would invoke the
pager,
rather than just always using the terminal window size.

Are you saying you'd want to set the threshold to *more* than the
window
height? Why?

Because I might be quite happy with 100 or 200 lines I can just
scroll in my terminal's scroll buffer, but want to use the pager for
more than that. This is useful especially if I want to scroll back
and see the results from a query or two ago.

This patch shows more or less what I had in mind.

However, there is more work to do. As Tom noted upthread, psql's
calculation of the number of lines is pretty bad. For example, if I do:

\pset pager_min_lines 100
select * from generate_series(1,50);

the pager still gets invoked, which is unfortunate to say the least.

So I'm going to take a peek at that.

The over-eager invocation of the pager due to double counting of lines
got fixed recently, so here's a slightly updated patch for a
pager_min_lines setting, including docco.

The assigned reviewer hasn't done a review and hasn't responded to
email. If there are no other comments I propose to commit this shortly.

cheers

andrew

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On 2014-12-21 14:22:10 -0500, Andrew Dunstan wrote:

@@ -301,11 +301,11 @@ slashUsage(unsigned short int pager)
* show list of available variables (options) from command line
*/
void
-helpVariables(unsigned short int pager)
+helpVariables(unsigned short int pager,	int pager_min_lines)
{
FILE	   *output;

Odd space before pager_min_lines.

Without having actually tried it, it looks clean enough to me. If
there's more pager options we might at some point introduce a pager
options struct instead adding more options to PageOutput. But for now it
seems ok enough.

Greetings,

Andres Freund

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Andres Freund <andres@2ndquadrant.com> writes:

Without having actually tried it, it looks clean enough to me. If
there's more pager options we might at some point introduce a pager
options struct instead adding more options to PageOutput. But for now it
seems ok enough.

My reaction is that now would be the time to do that, really. This is
messing up the argument lists of what seems like a whole lot of functions,
and I have little faith that this is the last argument we'll need to add.

regards, tom lane

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