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Allow fractional input values for integer GUCs, and improve rounding logic.

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Historically guc.c has just refused examples like set work_mem = '30.1GB',
but it seems more useful for it to take that and round off the value to
some reasonable approximation of what the user said.  Just rounding to
the parameter's native unit would work, but it would lead to rather
silly-looking settings, such as 31562138kB for this example.  Instead
let's round to the nearest multiple of the next smaller unit (if any),
producing 30822MB.

Also, do the units conversion math in floating point and round to integer
(if needed) only at the end.  This produces saner results for inputs that
aren't exact multiples of the parameter's native unit, and removes another
difference in the behavior for integer vs. float parameters.

In passing, document the ability to use hex or octal input where it
ought to be documented.

Discussion: https://postgr.es/m/1798.1552165479@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2019-03-11 19:13:46 -04:00
parent fe0b2c12c9
commit 1a83a80a2f
4 changed files with 74 additions and 34 deletions
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18
doc/src/sgml/config.sgml
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@ -51,14 +51,21 @@
In general, enclose the value in single quotes, doubling any single
quotes within the value. Quotes can usually be omitted if the value
is a simple number or identifier, however.
(Values that match a SQL keyword require quoting in some contexts.)
</para>
</listitem>
<listitem>
<para>
<emphasis>Numeric (integer and floating point):</emphasis>
A decimal point is permitted only for floating-point parameters.
Do not use thousands separators. Quotes are not required.
Numeric parameters can be specified in the customary integer and
floating-point formats; fractional values are rounded to the nearest
integer if the parameter is of integer type. Integer parameters
additionally accept hexadecimal input (beginning
with <literal>0x</literal>) and octal input (beginning
with <literal>0</literal>), but these formats cannot have a fraction.
Do not use thousands separators.
Quotes are not required, except for hexadecimal input.
</para>
</listitem>
@ -99,6 +106,13 @@
</para>
</listitem>
</itemizedlist>
If a fractional value is specified with a unit, it will be rounded
to a multiple of the next smaller unit if there is one.
For example, <literal>30.1 GB</literal> will be converted
to <literal>30822 MB</literal> not <literal>32319628902 B</literal>.
If the parameter is of integer type, a final rounding to integer
occurs after any units conversion.
</para>
</listitem>