Re: proposal: rounding up time value less than its unit.

On 07/10/2014 09:52 AM, Tomonari Katsumata wrote:
> Hi,
>
> Several couple weeks ago, I posted a mail to pgsql-doc.
> http://www.postgresql.org/message-id/53992FF8.2060702@po.ntts.co.jp
>
> In this thread, I concluded that it's better to
> round up the value which is less than its unit.
> Current behavior (rounding down) has undesirable setting risk,
> because some GUCs have special meaning for 0.
>
> And then I made a patch for this.
> Please check the attached patch.

The patch also rounds a zero up to one. A naked zero with no unit is not
affected, but e.g if you have "log_rotation_age=0s", it will not disable
the feature as you might expect, but set it to 1 minute. Should we do
something about that?

If we're going to explain the rounding up in the manual, we also need to
explain the normal rule, which is to round down. How about this:

--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -44,6 +44,15 @@
(seconds), <literal>min</literal> (minutes), <literal>h</literal>
(hours), and <literal>d</literal> (days). Note that the multiplier
for memory units is 1024, not 1000.
+
+ <para>
+ If a memory or time setting is specified with more precision than the
+ implicit unit of the setting, it is rounded down. However, if
rounding
+ down would yield a zero, it is rounded up to one instead. For
example,
+ the implicit unit of <varname>log_rotation_age</varname is
minutes, so if
+ you set it to <literal>150s</literal>, it will be rounded down to two
+ minutes. However, if you set it to <literal>10s</literal>, it will be
+ rounded up to one minute.
</para>

- Heikki