Fractions in GUC variables

On 12/07/2014 11:48 AM, John Gorman wrote:

This patch implements the first wiki/Todo Configuration Files item
"Consider normalizing fractions in postgresql.conf, perhaps using '%'".

The "Fractions in GUC variables" discussion is here.

Oh, this is nice! Thanks for working on it.

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On Mon, Dec 8, 2014 at 4:48 AM, John Gorman <johngorman2@gmail.com> wrote:

The attached patch applies cleanly against master and passes all regression
tests including two new tests in guc.sql.

Please be sure to register your patch to the upcoming commit fest,
this way it will not fall into oblivion and will get some feedback:
https://commitfest.postgresql.org/action/commitfest_view?id=25
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On 12/07/2014 09:48 PM, John Gorman wrote:

This patch implements the first wiki/Todo Configuration Files item
"Consider normalizing fractions in postgresql.conf, perhaps using '%'".

The "Fractions in GUC variables" discussion is here.

/messages/by-id/467132CF.9020501@enterprisedb.com

Ah, flash from the past :-). Thanks for looking into this.

The bgwriter_lru_percent and bgwriter_all_percent settings are gone now,
so the original reason to do this is gone. We consistently use fractions
in the GUCs now.

This patch implements expressing GUC variables as percents in
postgresql.conf.

autovacuum_vacuum_scale_factor = 20% # percent of table size before vacuum
autovacuum_analyze_scale_factor = 10% # percent of table size before
analyze

As you can see the postgresql.conf file and the documentation read more
naturally. I added a regression test to guc.sql. The sql interface also
accepts both numeric and percent forms although the percent form must be
quoted because '%' is an operator.

show cursor_tuple_fraction; --> 10%
set cursor_tuple_fraction = .15; --> 15%
set cursor_tuple_fraction = '33%'; --> 33%

I tagged four configuration variables to display as percents.

I'm not sure I agree that percentages are better than fractions. I'd
vote a -0.5 for changing the default display format. There isn't much
harm in accepting them as a secondary format, though.

We should only accept percentages for settings where that makes sense.
It is sensible for most of the PGC_REAL settings, but not so much for
geqo_selection_bias or seed, for example.

Overall, I feel that this isn't really worth the trouble. We use
fractions consistently now, so there isn't much room for confusion over
what the current values mean. Using a percentage might be more familiar
for some people, but OTOH you'll have to get used to the fractions
anyway, unless we change the default output format too, and I'm not in
favour of doing that. I suggest that we just drop this, and remove the
TODO item.

- Heikki

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On 12/15/14 8:56 AM, Heikki Linnakangas wrote:

show cursor_tuple_fraction; --> 10%
set cursor_tuple_fraction = .15; --> 15%
set cursor_tuple_fraction = '33%'; --> 33%

I tagged four configuration variables to display as percents.

I'm not sure I agree that percentages are better than fractions. I'd
vote a -0.5 for changing the default display format. There isn't much
harm in accepting them as a secondary format, though.

Agreed with not changing the default output. Everyone is used to it,
and there is no reason why the percent output would be intrinsically better.

We should only accept percentages for settings where that makes sense.
It is sensible for most of the PGC_REAL settings, but not so much for
geqo_selection_bias or seed, for example.

Right. But then this feature would get more complicated, as opposed to
supposedly making things simpler.

Overall, I feel that this isn't really worth the trouble. We use
fractions consistently now, so there isn't much room for confusion over
what the current values mean. Using a percentage might be more familiar
for some people, but OTOH you'll have to get used to the fractions
anyway, unless we change the default output format too, and I'm not in
favour of doing that. I suggest that we just drop this, and remove the
TODO item.

Agreed.

The patch is sound as far as it goes (I might be inclined to accept
whitespace between number and % sign), but given the above points and
the original reason for it having been eliminated, I'm inclined to drop it.

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On Mon, Dec 15, 2014 at 10:19:19AM -0500, Peter Eisentraut wrote:

Overall, I feel that this isn't really worth the trouble. We use
fractions consistently now, so there isn't much room for confusion over
what the current values mean. Using a percentage might be more familiar
for some people, but OTOH you'll have to get used to the fractions
anyway, unless we change the default output format too, and I'm not in
favour of doing that. I suggest that we just drop this, and remove the
TODO item.

Agreed.

The patch is sound as far as it goes (I might be inclined to accept
whitespace between number and % sign), but given the above points and
the original reason for it having been eliminated, I'm inclined to drop it.

TODO item removed.

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EnterpriseDB http://enterprisedb.com

+ Everyone has their own god. +

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On 12/7/14, 1:48 PM, John Gorman wrote:

This patch implements the first wiki/Todo Configuration Files item "Consider normalizing fractions in postgresql.conf, perhaps using '%'".

FWIW, I've reviewed this (should have read the thread first :/). It looks clean, passes make check and works as advertised. I also looked at what config options were set to be % and they make sense. Looking for .[0-9] in postgresql.conf, the only GUCs I saw where % didn't make sense was the two geco GUCs Heikki mentioned.

One thing I don't like is the need to wrap a %-based SET in quotes, but we need to do that for all GUCs that include units, so presumably there's no good way around it.
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On Tue, Dec 16, 2014 at 12:19 AM, Peter Eisentraut <peter_e@gmx.net> wrote:

On 12/15/14 8:56 AM, Heikki Linnakangas wrote:

Overall, I feel that this isn't really worth the trouble. We use
fractions consistently now, so there isn't much room for confusion over
what the current values mean. Using a percentage might be more familiar
for some people, but OTOH you'll have to get used to the fractions
anyway, unless we change the default output format too, and I'm not in
favour of doing that. I suggest that we just drop this, and remove the
TODO item.

Agreed.

The patch is sound as far as it goes (I might be inclined to accept
whitespace between number and % sign), but given the above points and
the original reason for it having been eliminated, I'm inclined to drop it.

+1.
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Michael

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